First photosynthetic characterization of the giant kelp Macrocystis pyrifera from the Comau Fjord, Northern Patagonia region

First photosynthetic characterization of the giant kelp Macrocystis pyrifera from the Comau Fjord, Northern Patagonia region | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article First photosynthetic characterization of the giant kelp Macrocystis pyrifera from the Comau Fjord, Northern Patagonia region Mauricio Palacios, Mathias Hüne, Iván Gómez This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6456951/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract Giant kelp ( Macrocystis pyrifera ) covers large coastal areas along the Comau Fjord (Northern Patagonia), following different environmental gradients that determine its structural complexity. In the present study, we compared the morphological (thallus length and biomass, holdfast diameter, blade morphology, etc.) and photobiological characteristics based on fluorescence (Effective Quantum Yield and P-I Curve Parameters) of six populations along the coast of Comau Fjord in three areas: Lilihuapi Island, Cahuelmo sector and Comau Fjord interior. The main results show that along the Comau Fjord, we found different structural conformations of M. pyrifera populations, where only at the mouth of the fjord was it possible to record a well-established “kelp forest”, while in its interior the “cords” parallel to the coastline predominated. The major differences between these types of populations of M. pyrifera populations were related to the shape of the blades ( e.g. , > blade areas in 4-CF, 5-Cf, and 6-Cf), being this a photo-acclimation strategy that responds to a marked environmental gradient along the fjord, in addition to particular geomorphology, surrounded by mountain ranges, which limits the availability of light during the pre-winter period, which translates into a balance along the Comau Fjord in its photosynthetic efficiency (α = 0.41, p < 0.05 between sites) of optimizing light absorption. These adaptations help the algae to resist local and seasonal changes in water column conditions, adjusting its light use to low levels, similar to Antarctic brown algae, and cope with low light conditions. This type of study corresponds to the first morphological and physiological characterization of natural populations of M. pyrifera in this area of Northern Patagonia and underlines the importance of continuing to collect information on a broader spatio-temporal scale to understand how stressors influence the morphology and physiology of these populations in a region that is suffering the consequences of global climate change, such as Northern Patagonia, and that is also intensely impacted by local anthropogenic activities. Giant kelp forest Comau Fjord Photobiological characteristics Blade morphometry Photo-acclimation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction The populations of the giant kelp Macrocystis pyrifera (Phaeophyceae, Laminariales) represent the key component of the benthic ecosystems around vast regions along the northern and southern eastern Pacific, south Atlantic coast of Argentina and Malvinas islands, New Zealand, southern Australia, and the sub-Antarctic islands (Huovinen and Gómez 2012 ; Macaya and Zucarello 2010). In the Southern Chilean Patagonia, it is possible to observe extensive and highly productive forests of M. pyrifera , especially in inlets, channels, and fjords (Dayton 1985 , Santelices and Ojeda 1984 a, b; Friedlander et al. 2020 , 2021 ) where they can cover more than 4,840.7 km 2 (Mora-Soto et al. 2020 ). Much of the ecological success of M. pyrifera comes from a remarkable morphological and functional plasticity that allows the species to colonize and dominate in different habitats marked by sharp environmental gradients (Graham et al. 2007 ). A remarkable physiological acclimation to environmental shifts has been commonly reported for populations of the North Pacific coast (Clendennen et al. 1996 ; Cabello-Pasini et al. 2000 ; Umanzor et al. 2021 ) and various sub-Antarctic regions (Cruces et al. 2012 ; Buschmann et al. 2014 ; Mabin et al. 2019 ; Fernández et al. 2021 ). In this context, the morpho-functional traits of this species, especially its large size and massive canopy structure, determining marked longitudinal gradients in photo-acclimation and photosynthetic performance, are key factors explaining this ecophysiological versatility (Lobban 1978 ; Gerard 1986 ; Lüning 1990 ; Colombo-Pallota et al. 2006). Thus, giant kelp forests formed by large individuals become a highly complex system on their own, which determines not only its intrinsic patterns in photosynthesis, growth, and productivity but also can buffer the abiotic impacts with significant consequences for the associated marine community (Reed and Foster 1984 ; Arkema et al. 2009 ). Due to that, the architecture of the kelp forest can vary in response to habitat due to local differences in environmental factors (Stephens et al. 2019 ). It is possible to argue that morpho-functionality, measured as photosynthetic responses, can also vary and thus give insights into the adaptation status of the different giant kelp populations across environmental gradients in extensive geographic areas such as Chilean Patagonia. The Comau Fjord (42°22`S), in the northern Patagonian region, comprises 41 km and an average width of 4.5 km with a maximum depth of 500 m (Mayr et al. 2011 ; Huovinen et al. 2016 ) and is considered a unique ecosystem with high primary productivity, high benthic biomass stock, high turnover rates, and high diversity, including abundant presence of rare and threatened species, for example, dense populations of cold-water corals (Häussermann et al. 2013 ; Garcia-Herrera et al. 2020; Beck et al. 2022 ). These ecological characteristics, among others, have allowed the establishment of a Marine Protected Area (MPA) of 4.15 km 2 in extension (MPA “Fiordo Comau - San Ignacio de Huinay”). However, these conservation efforts have not precluded direct and indirect anthropogenic pressures derived mainly from aquaculture activities (especially salmon farming, Buschmann et al. 2006 ), industrial fishing, and climate change (Försterra et al. 2017 ; Iriarte 2018 ), generating a 75% loss of species abundance in the last 10 years (Anbleyth-Evans et al. 2020 ). In contrast with the southern Patagonian fjords, where M. pyrifera forms luxuriant forests (Dayton 1985 ; Palacios et al. 2021 ; Mora-Soto et al. 2021 ), in the estuarine Comau Fjord, marked by a sharp water column stratification due to massive freshwater runoff from rainfall and rivers (Lloncochaigua and Vudodahue rivers) the populations of the giant kelps are scattered in patches through the shallow subtidal between 3 to 6 meters depth (Dayton 1985 ; Villalobos et al. 2021 ). Due to this, benthic photosynthesis can be possible to have considerable depth as light penetration (PAR) can reach 20 m, but with strong optical stratification (Huovinen et al. 2016 ). Based on few studies on the marine ecology of this site, has been suggested that the dominance of other conspicuous benthic organisms, e.g. cold-water corals, could substitute the foundational role of giant kelps by modulating the environment, providing a highly complex biogenic habitat and maintaining a distinct self-organized habitat for the associated biota (Försterra et al. 2016 ). However, due to their size and coverage, it is reasonable to argue that the giant kelp is a key species in these environments, thus highlighting the importance of understand its morpho-functionality to define its position in the benthic framework and its contribution to the benthic productivity. This study is aimed to characterize for the first time the morphology and photosynthesis of M. pyrifera from six locations along the Comau Fjord, which will be associated with the local abiotic variables ( e.g. , temperature, light). We address the hypothesis that the environmental settings, especially those associated with the column stratification, can exert a strong impact on the morpho-functionality of M. pyrifera across a relatively reduced scale. These results are relevant to understand better the status of these populations of M. pyrifera and their ecosystem functions in an understudied region affected by anthropogenic impacts and to gain insights into the physiological factors underlying the remarkable capacity of this species to thrive across habitats with highly contrasting environmental conditions, especially in one region of Chilean Patagonia cataloged as an area of high value for marine conservation (Gómez et al. 2024 ) is a global urgency (Arafeh-Dalmau et al. 2024 ), and an area that is being affected by industrial activities that generate a high environmental impact. Materials and Methods Study sites M. pyrifera samples were collected by SCUBA diving in May 2024, during the autumn. Six sites with the presence of M. pyrifera were selected, distributed along the coast of the Comau Fjord (41 km), considering the oceanic influence from the Pacific to the interior of the fjord where the influence of the Vodudahue River is much more permanent and where they develop in different types of habitats. These M. pyrifera populations at different sites are subject to dissimilar abiotic conditions ( e.g. , temperature and salinity, Rossbach et al. 2021 ) and should exhibit different morphological characteristics and physiological performance ( e.g. , Labbé et al. 2024 ). Along the Comau Fjord, we identified three areas: 1) Li: Lilihuapi Island, 2) CCh: Cahuelmo Sector and 3) Cf: Inside of the Comau Fjord (Fig. 1 A). Also, the subtidal M. pyrifera assemblages were classified regarding their distribution and coverage into i) "Patches" when they correspond to isolated aggregates of M. pyrifera (Fig. 1 B), ii) "Cordon" when they are arranged parallel to the coastline (Fig. 1 C) and iii) "Kelp forests" when they cover an area larger than 1 hectare (Fig. 1 D). All M. pyrifera populations along the fjord were settled at different shallow depths between 3 to 5 meters and associated with different habitats (Table 1 ). Sea surface temperature (SST °C) was estimated using the 4 km and 9 km MODIS L3 layer, which shows nighttime SST, and the 4 km MODIS L3 layer, which shows global daytime sea SST ( https://worldview.earthdata.nasa.gov/ , Minnett et al. 2004 ). Table 1 Description of the characteristics of the habitat where populations of M. pyrifera were identified in the inside of the Comau Fjord, Los Lagos region, Chile. Data source for Sea Surface Temperature (SST °C) for the year 2023 (Minnett et al. 2004 ); Salinity (PSU) for 2022 May (Beck et al. 2022 ); Photosynthetically Active Radiation (PAR) up to 6 meters depth for 2011 February (Laudien et al. 2017 ). Sites Code Latitud Longitud Associated habitat Depth (m) SST (°C) Salinity (PSU)* PAR [µmol/m − 2 s − 1 ] Type of population Lilihuapi Island 1-LI 42°09,35' 72°35,82' Mytilid kelp paches wall 4 13.9 31.51 285.6 Patch Cahuelmo Channel 2-CCh 42°14,91' 72°26,94' Sand and rocks 3.5 14.0 31.5 Settled forest 3-CCh 42°15,15' 72°25,30' Rocks and Boulders 5 14.8 Patch Comau Fjord 4-Cf 42°20,64' 72°27,42' 45° vertical rock wall 3 14.7 30.4 194.9 Cordon 5-Cf 42°17,87' 72°31,16' 45° vertical rock wall 3 13.7 30.6 Cordon 6-Cf 42°25,97' 72°25,13' Boulders 3 14.6 31.01 Cordon Morphometric characterization of the thallus During autumn, sporophyte total biomass, total length, stipes numbers (Fig. 2 A .1 ), and holdfast maximum height and diameter (Fig. 2 A .2 ) of the 126 individuals of M. pyrifera for each site; 1-LI (n = 19), 2-CCh (n = 7), 3-CCh (n = 21), 4-Cf (n = 25), 5-Cf (n = 13) and 6-Cf (n = 41). At each site, blades of M. pyrifera were categorized into two zones along the longitudinal profile of the thallus, apical and basal (Fig. 2 A). Additionally, length, width, and area of different blades from each zone were determined to identify morphological differentiation patterns along the fjord (Fig. 2 B). The blade area was estimated by analyzing digital photographs captured with a NIKON D3200 camera in the field on a white surface (contrast), and vectorized using the free ImageJ software (version 1.45, W. Rasband, US National Institutes of Health, Bethesda, Maryland, USA, http://imagej.nih.gov/ij/ ). Determination of solar radiation in underwater light field from Comau Fjord Seasonal variability for the summer (2023–2024) and autumn (2024) of UV-B (280–315 nm), UV-A (315–400 nm), and photosynthetically active radiation (PAR; 400–700 nm) at the different sites was estimated using the Tropospheric Ultraviolet and Visible (TUV) Radiation Model (Madronich and Flocke, 1999 ) ( https://www.acom.ucar.edu/Models/TUV/Interactive_TUV ). To obtain the seasonal values, the maximum value of the day (solar noon) with an ozone layer of 298 DU for autumn and 261 for summer. Measurements were taken every 10 days per month between December 2023 and May 2024. For the calculations, elevation at sea level, low albedo (0.1), typical aerosol profile (standard model configuration), and clear conditions (no clouds) were considered. Measurements were taken every 10 days per month from May 2024 to December 2023. The percentage of radiation attenuation inside the fjord was determined from the database available for the Comau Fjord generated from previous oceanographic campaigns (Laudien et al. 2017 ). Chlorophyll fluorescence The effective quantum yield of Chl a fluorescence of photosystem II (Φ PSII ) was determined in vivo with a submergible Pulse Amplitude Modulation (PAM) fluorometer (Diving PAM; Walz, Effeltrich, Germany). Measurements were carried out following a longitudinal profile from apical to basal blades. The photosynthetic characteristics of blades from the different sites and depths were determined through photosynthesis vs. irradiance (P-E) curves, based on maximum electron transport rate (ETR max ), the initial slope indicating the efficiency of photochemistry (α), and the maximal irradiance for ETR saturation (E k ) using the formula: $$\:ETR=\:{{\Phi\:}}_{PSII}\:\text{x}\:{E}_{PAR}\:\text{x}\:A\:\text{x}\:{F}_{II}$$ 1 where Φ PSII is the effective quantum yield of fluorescence, E PAR is the intensity of the actinic light, A the blade absorptance, and F II the fraction of Chl a associated with the electrons from photosystem II (PSII) to incorporate one CO 2 molecule. In brown macroalgae this value is 0.5 (Grzymski et al. 1997 ). The absorptance was measured under sunlight by placing the blades (n = 12) on a Li-190R quantum sensor (LI-COR Biosciences, Lincoln, NE, USA) according to the formula: $$\:A=1-T-R$$ 2 where T is the transmittance (light transmitted through the blade), and R is the reflectance (reflected fraction). A nonlinear hyperbolic tangent function (Jassby and Platt 1976 ) was used to estimate the different photosynthetic parameters: $$\:ETR=\:{ETR}_{max}\:\text{x}\text{tanh}(\alpha\:\:\text{x}\frac{E}{{ETR}_{max}})$$ 3 where ETR max is the maximum ETR, tanh is the tangent function, α is the initial slope of the ETR–E curve. The saturation irradiance for the photosynthetic electron transport (E k ) was calculated as the intercept between α and ETR max . Statistical analysis The differences in blade morphology, and chlorophyll fluorescence based photochemical parameters between populations (LI, CCh and Cf), and blades (apical and basal) were tested using analysis of variance (ANOVA). post hoc analysis (Tukey's HSD) was performed when significant differences were detected ( p < 0.05). Assumptions such as homogeneity of variances and normality were examined with Levene and Shapiro-Wilks tests. For non-parametric data, the Kruskal-Wallis tests at a level of significance of α = 0.05 were applied. The relationship between multiple physiological and morphological traits (maximum electron transport rate, photosynthetic efficiency, and maximal irradiance for ETR saturation), environmental parameters (water temperature, salinity, type of habitat), and categorical groups (populations type) assessed using Principal Component Analysis (PCA). The factor coordinates of variables and cases, as well as the eigenvalues and variable-factor correlations, were estimated using the means group. Besides, PCA was using the prcomp function (library stats). Figures were generated using the R library factoextra , and the fviz_pca_var and fviz_pca_biplot functions. All analyzes were performed with the routines defined in the R version 4.4.2 platform (R Core Team 2024 ). Results Size, Biomass and holdfast of thallus Size varied between 0.71 and 3.19 m, with the plants of Lilihuapi Island (1-Li) exhibiting the smallest sizes ( Table S1 ). The size of the plants shows significant differences between sites, marked by larger population sizes in the Cahuelmo 2 sector (2-CCh) ( p < 0.0001; Fig. 3 A and Table 2 ). The individual wet biomass averaged between 58.95 and 554.70 g ( Table S1 ), with maximum values measured at Cahuelmo 2 (2-CCh) and minima in the Lilihuapi Island (1-Li) ( p = 0.0003; Fig. 3 B and Table 2 ). The holdfast was the parameter with the least marked differences between sites (diameter, p = 0.0033; height, p = 0.0040, Table 2 ). In general, the mean values of maximum holdfast diameter measured did not exceed 3 cm, varying between 1.63 and 2.97 cm (Fig. 3 C and Table S1 ), while holdfast height did not exceed 2 cm, with values between 0.91 and 1.79 cm (Fig. 3 D and Table S1 ). In the two parameters the highest measurements were recorded in the Cahuelmo sector (2-CCh) and Comau Fjord 5 (5-Cf). For the number of stipes, the counts do not exceed 4 stipes per plant, with values between 1.95 and 3.71 stipes (Fig. 3 E and Table S1 ), with significant differences between sites ( p = 0.0033, Table 2 ) marked by the highest stipe counts in the Cahuelmo sector (2-CCh, 3CCh). Finally, the reproductive status of M. pyrifera in the different monitoring sites along the Comau Fjord shows a high proportion of reproductive individuals in the sites of Lilihuapi Island (1-Li with 68% reproductive individuals) and sector Cahuelmo 2 (2-CCh with 100% reproductive individuals), which are the populations of M. pyrifera with more significant influence of the Pacific Ocean ( Fig. S1 and Table S1 ). The size distribution of M. pyrifera along the fjord shows clear segregation concerning the type of population, where the kelp forest in the Cahuelmo 2 sector (2-CCh) shows a greater amount of data in lengths of 3.2 meters, while the populations classified with "patches" and "cords" the mode of the data are between 0.62 m and 1.75 m (Fig. 4 A). The wet biomass distribution shows the same pattern, where the site in the Cahuelmo 2 sector (2-CCh) has the highest biomass observed with 573.9 g, compared to the other sites classified as patches and cordons, where the wet biomass values are between 52.3 g and 72.9 g (Fig. 4 B). Blade morphometry The blades length, values was > 17 cm with obvious differences among sites ( Table S1 ), where the highest values were observed in the sites located in the interior of the Comau Fjord (4-Cf, 5-Cf and 6-Cf), marking significant differences with the other sites ( p < 0.0001; Fig. 5 A and Table 2 ). As for the width of the blades, the values varied between 3.43 and 8.48 cm ( Table S1 ), showing significant differences between sites ( p < 0.0001), which were grouped into three groups, with the lowest values recorded on Lilihuapi Island (1-Li), the average values in the Cahuelmo sector (2-CCh and 3-CCh) and the interior of the Comau Fjord (4-Cf, 5-Cf and 6-Cf) showed the widest leaves (Fig. 5 B and Table 2 ). In the case of blades area, the mean ranged from 40.6 to 211.0 cm 2 ( Table S1 ) with significant differences ( p < 0.0001) between sites and repeating the same pattern observed for blades width (Fig. 5 C and Table 2 ). Likewise, no differences in morphological features were observed in the apical and basal blades at sites 1-Li, 2 CCh and 3 CCh, a situation different from that recorded for the sites located inside the Comau Fjord (4-Cf, 5-Cf and 6-Cf) ( Table S2 ). Table 2 Results of analysis of variance (ANOVA) for comparisons between sampling sites considering morphometry of thallus and blades (n = 126 plant; n = 196 blades) of M. pyrifera in the Comau Fjord. The results of one-way ANOVA and Kruskal-Wallis tests for non-parametric data are included (α = 0.05). *DF degrees of freedom, SE standard error, MS mean squares, F F statistic; P values in bold indicate significant differences ( p F) Plant size 120 0.2458 0.2551 8.219 < 0.0001 Wet biomass 120 0.4918 0.1735 5.037 0.0003 Blade length 186 0.1739 0.2152 10.2 < 0.0001 Area blades 186 0.2530 0.4603 31.72 F) Holdfast diameter 5 17.766 0.0033 Holdfast height 5 17.766 0.0040 Stipe number 5 17.723 0.0033 Blade width 5 91.918 < 0.0001 Chlorophyll florescence-based photosynthesis Photochemical profiles determined in different populations along the Comau Fjord showed shade adapted characteristics. Ф PSII varied between 0.39 in algae from Comau Fjord 6 (6-Cf) and 0.57 in the population of Comau sector 3 (3-CCh) with significant differences between all sites ( p = 0.03) (Table 3 – 4 ). At the level of lamina type, significant differences ( p < 0.05) are observed in 4 sites (1-Li, 2-CCh, 3-CCh and 4-Cf), but without clear patterns with respect to apical and basal laminae. While for the sites located at the head of the Comau Fjord (5-Cf and 6-Cf) no significant differences ( p > 0.05) in this photochemical parameter are evident (Table 3 – 4 ). For ETR max a mean of 30.73 [µmol m − 2 s − 1 ] was obtained for all sites, however, in the interior of Comau Fjord 6 (6-Cf) showed significant differences ( p < 0.0001) with respect to the other sites with lower values. Values for this photosynthetic parameter ranged from 17.34 to 45.06 [µmol m − 2 s − 1 ] (Fig. 6 A and Table 3 – 4 ). The photosynthetic efficiency, estimated as α, averaged 0.41 [µmol e − 1 m − 2 s − 1 ] [µmol m − 2 s − 1 ] −1 for all sites, however, in Comau Fjord 4 inside (4-Cf) it was lower than in rest of the sites no significant differences were observed in this parameter ( p = 0.1316), where values varied between 0.33 and 0.51 [µmol e − 1 m − 2 s − 1 ] [µmol m − 2 s − 1 ] −1 (Fig. 6 B and Table 3 – 4 ). In the case of saturating irradiances (E k ), the values reached an average of 86.94 (µmol m − 2 s − 1 ), with significant differences ( p = 0.0062) between the three sectors of the Comau Fjord (Lilihuapi Island, Cahuelmo sector and Inside the Comau Fjord). The highest observed E k values were recorded in the Cahuelmo sector (2-CCh and 3-CCh) and the first point inside Comau Fjord 4 (4-Cf), and the lowest records of photochemistry saturation in algae at points 5 and 6 inside Comau Fjord (5-Cf = 62.04 µmol m − 2 s − 1 ; 6-Cf = 59.54µmol m − 2 s − 1 ) (Fig. 6 C and Table 3 – 4 ). Table 3 Fluorescence-based photochemical characterization of M. pyrifera across different sites and blade types (apical and basal) along a Comau Fjord. Effective quantum yield (Φ PSII ) was measured in situ using a Diving-PAM for a total of 96 blades . ETR-based P-E curve parameters (ETR max , α and E k ) correspond to mean values ± CI (n = 8). Abbreviations: Lilihuapi Island ( 1-Li ), Cahuelmo sector ( 2-CCh , 3-CCh ), Comau Fjord inside ( 4-Cf , 5-Cf and 6-Cf ). Different letters denote significant mean differences ( p < 0.05) according to post hoc Tukey's HSD test. Sites Effective quantum yield P-E curve parameters ETR max α E k (Ф PSII ) (µmol e − 1 m − 2 s − 1 ) [µmol e − 1 m − 2 s − 1 ] [µmol m − 2 s − 1 ] −1 (µmol m − 2 s − 1 ) 1-Li 0.52 ± 0.09(a) 32.04 ± 4.87 (a) 0.51 ± 0.08(a) 67.11 ± 21.91(a) 2-CCh 0.53 ± 0.08(a) 42.61 ± 11.88(a) 0.36 ± 0.09(a) 122.69 ± 35.66(a,b) 3-CCh 0.57 ± 0.08(a,b) 45.06 ± 10.68(a) 0.42 ± 0.04(a) 104.54 ± 17.68(a,c) 4-Cf 0.45 ± 0.08(a) 24.38 ± 5.20(b) 0.33 ± 0.14(a) 105.74 ± 67.24(a) 5-Cf 0.53 ± 0.08(a) 22.97 ± 9.32(b) 0.48 ± 0.20(a) 62.04 ± 44.79(a,c) 6-Cf 0.38 ± 0.09(a,c) 17.34 ± 3.13(b) 0.36 ± 0.22(a) 59.54 ± 28.35(a) Blades type Sites (Ф PSII ) 1-Li 2-CCh 3-CCh 4-Cf 5-Cf 6-Cf Apical 0.63 ± 0.11(a) 0.39 ± 0.08(a) 0.66 ± 0.12(a) 0.72 ± 0.13(a) 0.50 ± 0.11(a) 0.41 ± 0.16(a) Basal 0.45 ± 0.12(b) 0.73 ± 0.10(b) 0.46 ± 0.10(b) 0.40 ± 0.07(b) 0.56 ± 0.12(a) 0.35 ± 0.11(a) In situ irradiance (µmol m − 2 s − 1 ) 96.5 357.3 782.1 178.2 430.5 435.3 Table 4 Results of analysis of variance (ANOVA) for comparisons between sampling ( A ) sites considering physiological characteristics and ( B ) blade type (apical and basal) of M. pyrifera in the Comau Fjord (n = 8). The results of one-way ANOVA and Kruskal-Wallis tests for non-parametric data are included (α = 0.05). *DF degrees of freedom, SE standard error, MS mean squares, F F statistic; P values in bold indicate significant differences ( p F) ETR max 44 0.1455 0.5151 9.348 F) Ф PSII 5 12.264 0.0314 (B) ANOVA Sites DF SE MS F Pr(> F) 2-CCh 28 0.1648 0.5225 30.63 F) 1-Li 1 4.9703 0.0258 3-CCh 1 8.7518 0.0031 5-Cf 1 1.2601 0.2616 Multivariate analysis PCA indicated that dimension 1 accounted for 46.4% of the variability, while dimension 2 accounted for 21.7%. Together, both components accounted for 68.1% of the total variability of all variables studied (Fig. 7 ). Overall, correlations for the two dimensions discriminated between variables associated with blades morphology and variables related to photobiological characteristics for each site in Comau Fjord ( Fig. S2 ). PC1 was mainly related to the variability of sites located in the inside Comau Fjord (4-CCh, 5-CCh, 6-CCh), defined by a higher contribution of blades morphological variables and a decrease in effective quantum yield (Ф PSII ) (Fig. 7 and Fig. S2 ). PC2 defined the variability associated with M. pyrifera populations located at the entrance of the Comau Fjord (1-Li, 2-CCh, 3CCh). Here, higher contributions were observed for physiological variables (ETR max , E k , and α), mean annual sea surface temperature (SST°C), and higher holdfast diameter values defined the component (Fig. 7 and Fig. S2 ). Grouping the information by population type, we can observe that PC2 is related to “kelp forests” and “patch” where the physiological variables, in addition to the distribution of thallus morphological variables, especially for site 2-CCh (see Fig. 4 , “kelp forests”) show a more significant contribution. In contrast, PC1 is related exclusively to populations of M. pyrifera that are distributed in the form of a “cordon” where the increase in the values of the morphological variables of the blades shows a strong contribution (Fig. 7 ). Discussion Giant kelp morphology of the Comau Fjord In the present study, several indicators based on morphological traits of M. pyrifera ( e.g. , thallu size and wet biomass) did not reveal marked differences between populations when values were analyzed at the organism level, with the exception of the population present in sector 2 of Cahulemo (2-CCh) which was the only site where a population with a well recognizable “kelp forest” structure was identified (Fig. 4 ). However, morphometric variables of blades and physiological indicators ( e.g. , ETR max , α and E k ), correlated to different degrees with the type of M. pyrifera population present along the Comau Fjord (Fig. 7 ). This is especially evident in the segregation observed between the populations located inside the Comau Fjord (sites 4, 5 and 6) and those present at its mouth (Lilihuapi Island and Cahuelmo sector), which show clear differences linked to physiological traits and morphometric characteristics of the blades such as length, width and area (Fig. 5 ). To understand these observed patterns, it is necessary to understand the dynamics of variation of abiotic factors that occur within the Comau Fjord. In this sense, several studies have reported that the geomorphology of the fjord, with an extension of 41 km, shows a marked stratification of the water column in terms of salinity, temperature and PAR (Jantzen et al. 2013 ; Huovinen et al. 2016 ; Laudien et al. 2017 ; Villalobos et al. 2021 ; Rossbach et al. 2021 ; Beck et al. 2022 ). These strong variation along the fjord have been attributed to the macromareal environment of the fjord with tidal ranges of up to 7.5 m (Häussermann and Försterra 2009 ), which are intensified by strong annual fluctuations in position and intensity of solar radiation cycles, precipitation, and tidal mixing (Försterra 2009 ; Sobarzo-Bustamante 2009 ). In terms of adaptive strategy, as observed in Southern Patagonia (Huovinen et al. 2020 ; Palacios et al. 2021 ), these populations of the giant kelp M. pyrifera have developed morphofunctional responses, such as increasing the area of absorption of solar radiation ( e.g. , increasing the surface area of its blades), which allows it to withstand local and seasonal changes in environmental conditions along the Comau Fjord. Along these lines, such M. pyrifera populations, which withstand variations in abiotic conditions in the water column at different spatio-temporal scales, depend on the optical characteristics of the water (Gómez et al. 2005 ) that in turn, influence the availability of light for photosynthesis (Huovinen et al. 2011). This is reflected along the Comau Fjord, differentiating those populations present in the Lilihuapi Island and Cahuelmo sector from those located inland, and which can adjust morphological traits and physiological responses to cope with daily and seasonal variations in light and nutrients (Kaminsky et al. 2024 ), allowing it to minimize physiological damage like other populations of M. pyrifera studied in fjords of southern Patagonia (Palacios et al. 2021 ; Coral-Santacruz et al. 2024 ). At the same time have confirmed that the blades of M. pyrifera possess adaptive strategies in response to the conditions of their environment; for example, blades that are located on the surface are better adapted to a high-light environment, and those located in deeper areas are better adapted to a low light environment presenting dynamic photoinhibition of photosynthesis during midday and recovery of photosynthesis during the afternoon and/or evening (Buschmann et al. 2014 ). These blade qualities determine the demographic structure and architectural characteristics of M. pyrifera populations in response to the combination of internal factors and the impact of abiotic and biotic factors on specific traits (Layton et al., 2019 ). Photobiological traits of M. pyrifera : implications for functional local adaptation of plants across Comau Fjord The absorption of solar radiation by M. pyrifera takes place in its fronds, and its degree of efficiency is based, firstly, on the ability to harness that radiation, turning these macroalgae into black objects that absorb practically the entire spectrum of incident light in the water column (Lobban 1978 ; Lüning 1990 ). Second, a canopy structure organized in a multilayered frond system, which is morphologically and functionally analogous to the leaves of higher plants, thus representing structures highly specialized in light absorption. These qualities are key in an environment where seasonal variations in the incidence of solar radiation are as accentuated as those observed in Comau Fjord. Our analysis confirms that solar radiation from summer to autumn has a marked decrease in the whole area (Fig. 8 A), a stress factor that these populations of M. pyrifera must face during an annual cycle. The most striking photobiological feature in the M. pyrifera populations studied along the Comau Fjord was the low light requirement for photochemistry, indicating an adaptation to shade. Considering the geomorphological context of the fjord, that is marked by a strong light restriction due to the obstruction of solar radiation by the surrounding mountain ranges (Fig. 8 B) which causing a direct attenuation of solar radiation of ~ 32% ( Table S3 ), the algae show some general patterns: (a) photochemical efficiency (α) and effective quantum yield (Ф PSII ), did not vary significantly between sites; (b) ETR max and E k values were relatively higher in the algae of located at the mouth of the Comau Fjord (Lilihuapi Island and Cahuelmo sector), compared to the other sites located inside the fjord (4-Cf, 5-Cf, and 6-Cf). These results suggest site-dependent differences, mainly associated with the degree of exposure of the blades to solar radiation. However, when considering the types of blades along a depth gradient, no marked differences were found, except for the light requirements (E k ) in the populations distributed inside the Comau Fjord (5-Cf and 6-Cf), whose values were higher in the apical blades ( Fig. S2 and Table S4 ). Unlike populations measured in the Strait of Magellan (Puerto del Hambre; Marambio et al. 2017 ) and in the Beagle Channel (Yendegaia Fjord; Palacios et al. 2021 ), where M. pyrifera specimens exceed 15 m in length, the photobiological differences in the blades at the vertical level are evident and respond to a strategy of use of solar radiation along the water column. In contrast to what was observed in the Comau Fjord, the average length of M. pyrifera specimens did not exceed 1.5 m; apparently, adaptation to shade is a response of these populations that during the winter period must respond to low light conditions. The limited physiological studies carried out on populations of M. pyrifera in Northern Patagonia limit to establish with certainty how the photochemical responses of this type of macroalgae operate, even more so in the absence of seasonal studies. However, in other areas of southern Patagonia, some antecedents reveal that this species presents putative photochemical adaptations to cope with low light (Marambio et al. 2017 ; Ziemmann dos Santos et al. 2019), apparently constitutive and that for M. pyrifera populations in Comau Fjord, it could be the response mechanism to light limitation during pre-winter periods and where solar radiation winter penetration levels have already been characterized with attenuation coefficients (K dpar ) of 0.67 m − 1 and Z 1% reaching depths of 3.5 m (Huovinen et al. 2016 ). Light requirements for photochemical saturation < 50 µmol m − 2 s − 1 are common for M. pyrifera (Table 3 ), suggesting that this species adjusts light use to much lower levels than those existing in the field. This pattern resembles adaptations found in large Antarctic brown algae (Huovinen and Gómez 2013 ; Gómez et al. 2019 ). Adaptation to shade may be functional to cope not only with limited light during prolonged winter at high latitudes, during episodes of increased light attenuation due to sedimentation caused by storms or currents but also confer photobiological capabilities to extend the range to deeper locations (Gómez et al. 1997 ; Gómez and Huovinen 2015 ). This type of study, which characterizes for the first time the morphology and physiology of these natural populations of M. pyrifera , allows us to understand how the patterns of distribution and demographic structuring in response to dynamic change factors in northern Patagonia are and will be in the future. Furthermore, they reaffirm the importance of continuing to gather information at a broader spatio-temporal scale that allows us to understand how stressors condition the ecophysiology of these M. pyrifera populations in a region that is suffering the consequences of global climate change, such as Northern Patagonia, and that is also intensely impacted by local anthropogenic activities. Declarations Funding This work was made possible by Fundación Rewilding Chile, a Chilean non-profit financially supported by an extensive philanthropic network and the FONDAP IDEAL Center [Grant 15150003]; Fondecyt Proyect [Grant 1241571] awarded to IG. Author Contribution M.P.: Writing-original draft, Conceptualization, Investigation/bibliographic research, Methodology, Formal analysis, Review and editing. M.H.: Review and editing, Supervision, Resources, Funding acquisition, Project administration. I.G.: Methodology, Review and Editing, Resources. Acknowledgement We greatly appreciate the in-situ logistic support of the Fundación Rewilding Chile during our fieldwork in the Comau Fjord, in particular from team members J. Poblete, J.L. Kappes and J.T. Yakasovic. References Anbleyth-Evans J, Araos-Leiva F, Ther Ríos F, Segovia-Cortés R, Häussermann V, Aguirre-Muñoz C (2020). Toward marine democracy in Chile: Examining aquaculture ecological impacts through common property local ecological knowledge. Mar Policy 113: 103690. https://doi.org/10.1016/j.marpol.2019.103690 Arafeh-Dalmau N, Olgun-Jacobson C, Earle S, Bello M, Lagger C, Mora-Soto A, Pantano C, Palacios M, et al. (2024). Protect kelp forests. Science 386: 629-629. https://doi.org/10.1126/science.adr4814 Arkema KK, Reed DC, Schroeter SC (2009). Direct and indirect effects of giant kelp determine benthic community structure and dynamics. Ecology 90: 3126-3137. https://doi.org/10.1890/08-1213.1 Beck KK, Schmidt-Grieb GM, Laudien J, et al. (2022). Environmental stability and phenotypic plasticity benefit the cold-water coral Desmophyllum dianthus in an acidified fjord. Commun Biol 5: 683. https://doi.org/10.1038/s42003-022-03622-3 Buschmann AH, Pereda SV, Varela DA, Rodríguez-Maulén J, López A, González-Carvajal L, et al. (2014). Ecophysiological plasticity of annual populations of giant kelp ( Macrocystis pyrifera ) in a seasonally variable coastal environment in the Northern Patagonian Inner Seas of Southern Chile. J Appl Phycol 26: 837-847. https://doi.org/10.1007/s10811-013-0070-z Buschmann AH, Riquelme VA, Hernández-González MC, Varela D, Jiménez JE, Henríquez LA, Vergara PA, Guíñez R, Filún L (2006). A review of the impacts of salmonid farming on marine coastal ecosystems in the southeast Pacific. ICES J Mar Sci 63 (7): 1338-1345. https://doi.org/10.1016/j.icesjms.2006.04.021 Cabello-Pasini A, Aguirre-von-Wobeser E, Figueroa FL (2000). Photoinhibition of photosynthesis in Macrocystis pyrifera (Phaeophyceae), Chondrus crispus (Rhodophyceae) and Ulva lactuca (Chlorophyceae) in outdoor culture systems. J Photochem Photobiol B Biol 57: 169-78. https://doi.org/10.1016/S1011-1344(00)00095-6 Clendennen SK, Zimmerman RC, Powers DA, Alberte RS (1996). Photosynthetic response of the giant kelp Macrocystis pyrifera (Phaeophyceae) to ultraviolet radiation. J Phycol 32: 614-620. https://doi.org/10.1111/j.0022-3646.1996.00614.x Colombo-Pallotta MF, García-Mendoza E, Ladah LB (2006). Photosynthetic performance, light absorption, and pigment composition of Macrocystis pyrifera (Laminariales, Phaeophyceae) blades from different depths. J Phycol 42: 1225-1234. https://doi.org/10.1111/j.1529-8817.2006.00287.x Coral-Santacruz D, Méndez F, Marambio J, et al. (2024). Effects of glacial melting on physiological performance of Macrocystis pyrifera in the Fjord of the Mountains, Magellanic Sub-Antarctic ecoregion, Chile. J Appl Phycol 36: 3637-3648. https://doi.org/10.1007/s10811-024-03362-3 Cruces E, Huovinen P, Gómez I (2012). Phlorotannin and antioxidant responses upon short-term exposure to UV radiation and elevated temperature in three South Pacific kelps. Photochem Photobiol 88: 58-66. https://doi.org/10.1111/j.1751-1097.2011.01013.x Dayton PK (1985). The structure and regulation of some South American kelp communities. Ecol Monogr 55: 447-468. Fernández PA, Navarro JM, Camus C, et al. (2021). Effect of environmental history on the habitat-forming kelp Macrocystis pyrifera responses to ocean acidification and warming: a physiological and molecular approach. Sci Rep 11: 2510. https://doi.org/10.1038/s41598-021-82094-7 Försterra G, Häussermann V, Laudien J (2017). Animal forests in the Chilean fjords: Discoveries, Perspectives and Threats in Shallow and Deep Waters. In: Rossi S, Bramanti L, Gori A, Orejas Saco del Valle C (Eds) Marine Animal Forests: The Ecology of Benthic Biodiversity Hotspots. Springer International Publishing 277–313. https://doi.org/10.1007/978-3-319-21012-4_3 Försterra G, Häussermann V, Laudien J (2016). Animal Forests in the Chilean Fjords: Discoveries, Perspectives and Threats in Shallow and Deep Waters. In: Rossi S, Bramanti L, Gori A, Orejas Saco del Valle C (Eds) Marine Animal Forests Springer, Cham. https://doi.org/10.1007/978-3-319-17001-5_3-1 Försterra G (2009). Ecological and biogeographical aspects of the Chilean fjord region. In: Häussermann V, Försterra G (Eds) Marine Benthic Fauna of Chilean Patagonia (Santiago: Nature In focus), 61-76. Friedlander AM, Ballesteros E, Goodell W, Hüne M, Muñoz A, Salinas-de-León P, et al. (2021). Marine communities of the newly created Kawésqar National Reserve, Chile: From glaciers to the Pacific Ocean. PLoS One 16(4): e0249413. https://doi.org/10.1371/journal.pone.0249413 Friedlander AM, Ballesteros E, Bell TW, Caselle JE, Campagna C, Goodell W, et al. (2020). Kelp forests at the end of the earth: 45 years later. PLoS One. 15: e0229259. https://doi.org/10.1371/journal.pone.0229259 Garcia-Herrera N, Cornil A, Laudien J, Niehoff B, Höfer J, Försterra G, Richter C (2022). Seasonal and diel variations in the vertical distribution, composition, abundance and biomass of zooplankton in a deep Chilean Patagonian Fjord. PeerJ 10: e12823. https://doi.org/10.7717/peerj.12823 Gerard VA, 1986. Photosynthetic characteristics of giant kelp ( Macrocystis pyrifera ) determined in situ. Mar Biol 90: 473-482. Gómez I, Garcés-Vargas J, Garrido I, Huovinen P, Macaya E, Mellado MA, Navarro NP, Palacios M, Pardo LM, Soto D, Valdivia N, Navarro A (2024). Bosques Submarinos de la Patagonia. ISBN 978-956-418-537-8, 139 pp. Gómez I, Navarro NP, Huovinen P (2019). Bio-optical and physiological patterns in Antarctic seaweeds: a functional trait based approach to characterize vertical zonation Prog Oceanogr 174: 17-27 https://doi.org/10.1016/j.pocean.2018.03.013 Gómez I, Huovinen P (2015). Lack of physiological depth patterns in conspecifics of endemic Antarctic brown algae: A trade-off between UV stress tolerance and shade adaptation?. PLoS ONE 10(8): e0134440. https://doi.org/10.1371/journal.pone.0134440 Gómez I, Figueroa FL, Huovinen P, Ulloa N, Morales V (2005). Photosynthesis of the red alga Gracilaria chilensis under natural solar radiation in an estuary in southern Chile. Aquaculture 244 (1-4): 369-382. https://doi.org/10.1016/j.aquaculture.2004.11.037 Gómez I, Weykam G, Klöser H, Wiencke C (1997). Photosynthetic light requirements, metabolic carbon balance and zonation of sublittoral macroalgae from King George Island (Antarctica). Mar Ecol Prog Ser 149: 281-293. Graham MH, Vasquez JA, Buschmann AH (2007). Global ecology of the giant kelp Macrocystis . Oceanogr. Mar Biol Annu Rev 45: 39-88. Grzymski J, Johnsen G, Sakshaug E (1997). The significance of intracellular self-shading on the biooptical properties of brown, red, and green macroalgae. J Phycol 33: 408-414. https://doi.org/10.1111/j.0022-3646.1997.00408.x Häussermann V, Försterra G, Melzer RR, Meyer R (2013). Gradual changes of benthic biodiversity in Comau Fjord, Chilean Patagonia – lateral observations over a decade of taxonomic research. Spixiana 36 (2): 161-171 Häussermann V, Försterra G (2009). Marine Benthic Fauna of Chilean Patagonia: Illustrated Identification Guide. Santiago: Nature in Focus. Huovinen P, Ramírez J, Palacios M, Gómez I (2020). Satellite-derived mapping of kelp distribution and water optics in the glacier impacted Yendegaia Fjord (Beagle Channel, Southern Chilean Patagonia). Sci Total Environ 703: 135531. https://doi.org/10.1016/j.scitotenv.2019.135531 Huovinen P, Ramírez J, Gómez I (2016). Underwater Optics in Sub-Antarctic and Antarctic Coastal Ecosystems. PLoS ONE 11(5): e0154887. https://doi.org/10.1371/journal.pone.0154887 Huovinen P, Gómez I (2013). Photosynthetic characteristics and UV stress tolerance of Antarctic seaweeds along the depth gradient. Polar Biol 36: 1319-1332. https://doi.org/10.1007/s00300-013-1351-3 Huovinen P, Gómez I (2012). Cold-temperate seaweeds communities of the southern Hemisphere. In: Wiencke C, Bischof K (Eds) Seaweed Biology: Novel Insights into Ecophysiology, Ecology and Utilization (219) Ecological Studies, Springer. pp 293-313. https://doi.org/10.1007/978-3-642-28451-9_14 Huovinen P, Gómez I (2011). Spectral attenuation of solar radiation in Patagonian fjords and coastal waters and implications for algal photobiology. Cont Shelf Res 31: 254-259. https://doi.org/10.1016/j.csr.2010.09.004 Iriarte JL (2018). Natural and human influences on marine processes in Patagonian subantarctic coastal waters. Front Mar Sci 5: 360. https://doi.org/10.3389/fmars.2018.00360 Jantzen C, Laudien J, Sokol S, Försterra G, Häussermann V, Kupprat F, et al. (2013). In situ short-term growth rates of a cold-water coral. Mar Freshw Res 64: 631–641. https://doi.org/10.1071/MF12200 Jassby AD, Platt T (1976). Mathematical formulation of the relationship between photosynthesis and light for phytoplankton. Limnol Oceanogr 21: 540-547. Kaminsky J, Bagur M, Schloss IR, et al. (2024). Giant kelp ( Macrocystis pyrifera ) morphological and reproductive strategies in two contrasting sub-Antarctic forests. Mar Biol 171: 9. https://doi.org/10.1007/s00227-023-04341-x Laudien J, Jantzen C, Häussermann V, Försterra G, Sswat M, Baumgarten S, Richter C (2017). Physical oceanographic profiles of seven CTD casts from Gulf of Ancud into Comau Fjord in 2011 [dataset]. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, PANGAEA, https://doi.org/10.1594/PANGAEA.884120 Labbé BS, Fernández PA, Florez JZ, Buschmann AH (2024). Effects of pH, Temperature, and Light on the Inorganic Carbon Uptake Strategies in Early Life Stages of Macrocystis pyrifera (Ochrophyta, Laminariales). Plants 13: 3267. https://doi.org/10.3390/plants13233267 Layton C, Shelamoff V, Cameron MJ, Tatsumi M, Wright JT, Johnson CR (2019). Resilience and stability of kelp forests: The importance of patch dynamics and environment-engineer feedbacks. PLoS One. 14(1): e0210220. https://doi.org/10.1371/journal.pone.0210220 Lobban CS (1978). Translocation of 14C in Macrocystis pyrifera (giant kelp). Plant Physiol 61: 585-589. https://doi.org/10.1104/pp.61.4.585 Lüning K (1990). Seaweeds: Their Environment, Biogeography, and Ecophysiology. John Wiley and Sons, New York, 489 pp. Mabin C, Johnson C, Wright J (2019). Physiological response to temperature, light, and nitrates in the giant kelp Macrocystis pyrifera , from Tasmania, Australia. Mar Ecol Prog Ser 614: 1-19. https://doi.org/10.3354/meps12900 Macaya EC, Zuccarello GC (2010). DNA barcoding and genetic divergence in the giant kelp Macrocystis (Laminariales). J Phycol 46: 736-742. https://doi.org/10.1111/j.1529-8817.2010.00845.x Madronich S, Flocke S (1999). The role of solar radiation in atmospheric chemistry. In: Boule P (Eds) Environmental Photochemistry. The Handbook of Environmental Chemistry (2/2L) Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3- 540-69044-3_1 Marambio J, Rodríguez JP, Méndez F, Ocaranza P, Rosenfeld S, Ojeda J, Rautenberger R, Bischof K, Terrados J, Mansilla A (2017). Photosynthetic performance and pigment composition of Macrocystis pyrifera (Laminariales, Phaeophyceae) along a gradient of depth and seasonality in the ecoregion of Magellan, Chile. J Appl Phycol 29: 2575-2585. https://doi.org/10.1007/s10811-017-1136-0 Mayr CC, Försterra G, Häussermann V, Wunderlich A, Grau J, Zieringer M, Altenbach AV (2011). Stable isotope variability in a Chilean fjord food web: implications for N- and C-cycles. Mar Ecol Prog Ser 428: 89-104. https://doi.org/10.3354/meps09015 Minnett PJ, Brown OB, Evans RH, Key EL, Kearns EJ, Kilpatrick K, et al. (2004). Sea-surface temperature measurements from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on Aqua and Terra, IGARSS 2004. 2004 IEEE International Geoscience and Remote Sensing Symposium, Anchorage, AK, USA, 7: 4576-4579. https://doi.org/10.1109/IGARSS.2004.1370173 Mora-Soto A, Capsey A, Friedlander AM, Palacios M, Brewin PE, Golding N, et al. (2021). One of the least disturbed marine coastal ecosystems on Earth: spatial and temporal persistence of Darwin’s sub-Antarctic giant kelp forests. J Biogeogr 48: 2562.2577. https://doi.org/10.1111/jbi.14221 Mora-Soto A, Palacios M, Macaya EC, Gómez I, Huovinen P, Pérez-Matus A, Young M, Golding N, Toro M, Yaqub M, Macias-Fauria M (2020). A high-resolution global map of Giant kelp ( Macrocystis pyrifera ) forests and intertidal green algae (Ulvophyceae) with Sentinel-2 imagery. Remote Sens 12: 694. https://doi.org/10.3390/rs12040694 Palacios M, Osman D, Ramírez J, Huovinen P, Gómez I (2021). Photobiology of the giant kelp Macrocystis pyrifera in the land-terminating glacier fjord Yendegaia (Tierra del Fuego): a look into the future? Sci Total Environ 751: 141810. https://doi.org/10.1016/j.scitotenv.2020.141810 R Core Team (2024). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/ Reed DC, Foster MS (1984). The effects of canopy shading on algal recruitment and growth in a giant kelp forest. Ecology 65: 937-948. Rossbach S, Rossbach FI, Häussermann V, Försterra G, Laudien J (2021). In situ skeletal growth rates of the solitary cold-water coral Tethocyathus endesa from the Chilean Fjord region. Front Mar Sci 8: 757702. https://doi.org/10.3389/fmars.2021.757702 Santelices B, Ojeda FP (1984)a. Effect of canopy removal on the understory algal community structure of coastal forest of Macrocystis pyrifera from southern South America. Mar Ecol Prog Ser 14: 165-173. Santelices B, Ojeda FP (1984)b. Population dynamics of coastal forests of Macrocystis pyrifera in Puerto Toro, lsla Navarino, Southern Chile. Mar Ecol Prog Ser 14: 176-183. Sobarzo-Bustamante M (2009). The Southern Chilean fjord region: oceanographic aspects. In: Häussermann V, Försterra G (Eds.) Marine Benthic Fauna of Chilean Patagonia (Santiago: Nature In focus) 53-60. Stephens TA, Desmond MJ, Hepburn CD (2019). Biomass across space and tide: architecture of a kelp bed with implications for the abiotic environment. Hydrobiologia 82: 391-404. https://doi.org/10.1007/s10750-018-3788-4 Umanzor S, Sandoval-Gil J, Sánchez-Barredo M, Ladah LB, Ramírez-García MM, Zertuche-González JA (2021). Short-term stress responses and recovery of giant kelp ( Macrocystis pyrifera , Laminariales, Phaeophyceae) juvenile sporophytes to a simulated marine heatwave and nitrate scarcity. J Phycol 57: 1604-1618. https://doi.org/10.1111/jpy.13189 Villalobos VI, Valdivia N, Försterra G, Ballyram S, Espinoza JP, Wadham JL, Burgos-Andrade K, Häussermann V (2021). Depth-Dependent Diversity Patterns of Rocky Subtidal Macrobenthic Communities Along a Temperate Fjord in Northern Chilean Patagonia. Front Mar Sci 8: 635855. https://doi.org/10.3389/fmars.2021.635855 Ziemann dos Santos MA, Coelho de Freitas S, Moraes-Berneira L, Mansilla A, Astorga-España, MS, Colepicolo P, Martin Pereira de Pereira C (2019). Pigment concentration, photosynthetic performance, and fatty acid profile of sub-Antarctic brown macroalgae in different phases of development from the Magellan region, Chile. J Appl Phycol 31: 2629-2642. https://doi.org/10.1007/s10811-019-01777-x Additional Declarations No competing interests reported. Supplementary Files Palaciosetal2025Supplementarymaterial.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 05 Jul, 2025 Reviews received at journal 05 Jul, 2025 Reviewers agreed at journal 17 May, 2025 Reviews received at journal 06 May, 2025 Reviewers agreed at journal 23 Apr, 2025 Reviewers invited by journal 23 Apr, 2025 Editor assigned by journal 23 Apr, 2025 Submission checks completed at journal 23 Apr, 2025 First submitted to journal 15 Apr, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6456951","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":443506210,"identity":"7ac21c20-8610-41f5-b813-7208d6750fc4","order_by":0,"name":"Mauricio Palacios","email":"data:image/png;base64,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","orcid":"","institution":"Fundación Rewilding Chile","correspondingAuthor":true,"prefix":"","firstName":"Mauricio","middleName":"","lastName":"Palacios","suffix":""},{"id":443506211,"identity":"3ab78ba9-5814-4ba3-8c3f-c6eac3374e99","order_by":1,"name":"Mathias Hüne","email":"","orcid":"","institution":"Fundación Rewilding Chile","correspondingAuthor":false,"prefix":"","firstName":"Mathias","middleName":"","lastName":"Hüne","suffix":""},{"id":443506212,"identity":"07af2faa-b149-4fbf-814c-f3ff952824dd","order_by":2,"name":"Iván Gómez","email":"","orcid":"","institution":"Instituto de Ciencias Marinas y Limnológicas, Facultad de Ciencias, Universidad Austral de Chile","correspondingAuthor":false,"prefix":"","firstName":"Iván","middleName":"","lastName":"Gómez","suffix":""}],"badges":[],"createdAt":"2025-04-15 17:08:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6456951/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6456951/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":80828498,"identity":"780042da-4db1-45cc-bb5d-ae17bd8a50d7","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":5106249,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003eA\u003c/strong\u003e) Geographical location of the six populations of \u003cem\u003eM. pyrifera\u003c/em\u003e selected for the study along the Comau Fjord, where it was possible to identify populations distributed as (\u003cstrong\u003eB\u003c/strong\u003e) Patch, (\u003cstrong\u003eC\u003c/strong\u003e) Cordon and (\u003cstrong\u003eD\u003c/strong\u003e) Kelp forest. Abbreviations: Lilihuapi Island (\u003cstrong\u003e1-Li\u003c/strong\u003e), Cahuelmo sector (\u003cstrong\u003e2-CCh\u003c/strong\u003e, \u003cstrong\u003e3-CCh\u003c/strong\u003e), Comau Fjord interior (\u003cstrong\u003e4-Cf\u003c/strong\u003e, \u003cstrong\u003e5-Cf\u003c/strong\u003e and \u003cstrong\u003e6-Cf\u003c/strong\u003e). Underwater photograph \u003cstrong\u003eB-D\u003c/strong\u003e: Fundacion Rewilding Chile.\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/8cf30b12c62ed58e0e48fc47.png"},{"id":80828497,"identity":"370e8d81-b77f-4379-b46e-e28707baec30","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5231451,"visible":true,"origin":"","legend":"\u003cp\u003e(\u003cstrong\u003eA\u003c/strong\u003e) Morphology of \u003cem\u003eM. pyrifera\u003c/em\u003e illustrating the different morphometric variables evaluated along the Comau Fjord. Underwater photograph \u003cstrong\u003eA.1\u003c/strong\u003e indicates the stipes of \u003cem\u003eM. pyrifera\u003c/em\u003e and \u003cstrong\u003eA.2\u003c/strong\u003e indicates the maximum height and diameter of the holdfasts. (\u003cstrong\u003eB\u003c/strong\u003e) Different types of blades considered in the analysis. (\u003cstrong\u003eB\u003c/strong\u003e) Distribution of lamellae along a longitudinal profile of \u003cem\u003eM. pyrifera\u003c/em\u003e, in each lamella morphometric variables were evaluated including length, width and area of blades. Underwater Photographs: Mauricio Palacios, Illustration \u003cem\u003eM. pyrifera\u003c/em\u003e: Integration and Application Network (http://ian.umces.edu/media-library/).\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/a10f32ed4541dfce98671caa.png"},{"id":80828500,"identity":"0e329edc-0d30-4e2e-b2a9-4a1dabaadcdc","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1052674,"visible":true,"origin":"","legend":"\u003cp\u003eAnalysis of morphometric parameters show the (\u003cstrong\u003eA\u003c/strong\u003e) variation in individual total length (m), (\u003cstrong\u003eB\u003c/strong\u003e) holdfast diameter (cm), (\u003cstrong\u003eC\u003c/strong\u003e) stipes number, (\u003cstrong\u003eD\u003c/strong\u003e) wet biomass (kg/ind.) and (\u003cstrong\u003eE\u003c/strong\u003e) height holdfast individuals of \u003cem\u003eM. pyrifera\u003c/em\u003e from different sites along the Comau Fjord. Abbreviations: Lilihuapi Island (\u003cstrong\u003e1-Li\u003c/strong\u003e), Cahuelmo sector (\u003cstrong\u003e2-CCh\u003c/strong\u003e, \u003cstrong\u003e3-CCh\u003c/strong\u003e), Comau Fjord interior (\u003cstrong\u003e4-Cf\u003c/strong\u003e, \u003cstrong\u003e5-Cf\u003c/strong\u003e and \u003cstrong\u003e6-Cf\u003c/strong\u003e). Values are means ± C.I., n= 126. Different letters denote significant mean differences (\u003cem\u003ep \u003c/em\u003e\u0026lt; 0.05) among means according to post hoc Tukey's HSD test.\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/b50c86ab4c48476af0e5d494.png"},{"id":80828504,"identity":"0092534b-bf99-47f1-9214-8f158428a742","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":892423,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution (\u003cstrong\u003eA\u003c/strong\u003e) size (m) and (\u003cstrong\u003eB\u003c/strong\u003e) wet biomass (g) observed in \u003cem\u003eM. pyrifera\u003c/em\u003e individuals collected along the Comau Fjord. Abbreviations: Lilihuapi Island (\u003cstrong\u003e1-Li\u003c/strong\u003e), Cahuelmo sector (\u003cstrong\u003e2-CCh\u003c/strong\u003e, \u003cstrong\u003e3-CCh\u003c/strong\u003e), Comau Fjord interior (\u003cstrong\u003e4-Cf\u003c/strong\u003e, \u003cstrong\u003e5-Cf\u003c/strong\u003e and \u003cstrong\u003e6-Cf\u003c/strong\u003e). The vertical dotted line shows the mode of the data.\u003c/p\u003e","description":"","filename":"Figure4.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/94ed9cfeec8b5a12b11cc4fe.png"},{"id":80828988,"identity":"46e35831-7d36-4157-929f-f1b2cb407730","added_by":"auto","created_at":"2025-04-17 13:47:31","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":719087,"visible":true,"origin":"","legend":"\u003cp\u003eVariation in (\u003cstrong\u003eA\u003c/strong\u003e) length (m), (\u003cstrong\u003eB\u003c/strong\u003e) width (cm) and (\u003cstrong\u003eC\u003c/strong\u003e) area (cm\u003csup\u003e2\u003c/sup\u003e) of blades in \u003cem\u003eM. pyrifera\u003c/em\u003e from different sites along the Comau Fjord. Abbreviations: Lilihuapi Island (\u003cstrong\u003e1-Li\u003c/strong\u003e), Cahuelmo sector (\u003cstrong\u003e2-CCh\u003c/strong\u003e, \u003cstrong\u003e3-CCh\u003c/strong\u003e), insider Comau Fjord (\u003cstrong\u003e4-Cf\u003c/strong\u003e, \u003cstrong\u003e5-Cf\u003c/strong\u003e and \u003cstrong\u003e6-Cf\u003c/strong\u003e). Values are means ± C.I., n= 196. Different letters denote significant mean differences (\u003cem\u003ep \u003c/em\u003e\u0026lt; 0.05) among means according to post hoc Tukey's HSD test.\u003c/p\u003e","description":"","filename":"Figure5.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/92fe07edeaf5531b314cb900.png"},{"id":80828502,"identity":"bd730b22-8d0a-48ab-ad54-64c6032c0f45","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":666854,"visible":true,"origin":"","legend":"\u003cp\u003eFluorescence-based photochemical characterization of \u003cem\u003eM. pyrifera\u003c/em\u003e across different sites along a Comau Fjord measured in situ using a Diving-PAM. ETR-based P-E curve parameters, (\u003cstrong\u003eA\u003c/strong\u003e) Electron Transfer Rate-ETR\u003csub\u003emax\u003c/sub\u003e, (\u003cstrong\u003eB\u003c/strong\u003e) Photosynthetic efficiency-α and (\u003cstrong\u003eC\u003c/strong\u003e) Photochemical Saturation-E\u003csub\u003ek\u003c/sub\u003e. All recorded parameters correspond to mean values ± CI (n= 4). Abbreviations: Lilihuapi Island (\u003cstrong\u003e1-Li\u003c/strong\u003e), Cahuelmo sector (\u003cstrong\u003e2-CCh\u003c/strong\u003e, \u003cstrong\u003e3-CCh\u003c/strong\u003e), Comau Fjord inside (\u003cstrong\u003e4-Cf\u003c/strong\u003e, \u003cstrong\u003e5-Cf\u003c/strong\u003e and \u003cstrong\u003e6-Cf\u003c/strong\u003e). Different letters denote significant mean differences (\u003cem\u003ep \u003c/em\u003e\u0026lt; 0.05) according to post hoc Tukey's HSD test.\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/4be66a97994656c9e2e16110.png"},{"id":80828499,"identity":"689c65a3-b8c1-486c-86c5-ec9504914002","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":849460,"visible":true,"origin":"","legend":"\u003cp\u003eResults of the principal component analysis (PCA) biplot showing different morphological and physiological characteristics of\u0026nbsp;\u003cem\u003eM. pyrifera\u003c/em\u003e\u0026nbsp;from six sites along the Comau Fjord and population type. Abbreviations: Lilihuapi Island (1-Li), Cahuelmo sector (2-CCh, 3-CCh), Comau Fjord inside (4-Cf, 5-Cf and 6-Cf). Morphological characteristics,\u0026nbsp;\u003cstrong\u003eWB\u003c/strong\u003e: wet biomass,\u0026nbsp;\u003cstrong\u003eDH\u003c/strong\u003e: diameter holdfast,\u0026nbsp;\u003cstrong\u003eBL\u003c/strong\u003e: blade length,\u0026nbsp;\u003cstrong\u003eBW\u003c/strong\u003e: blade width and\u0026nbsp;\u003cstrong\u003eBA\u003c/strong\u003e: blade area. Physiological characteristics,\u0026nbsp;\u003cstrong\u003eФ\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ePSII\u003c/strong\u003e\u003c/sub\u003e: Effective quantum yield,\u0026nbsp;\u003cstrong\u003eETR\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003emax\u003c/strong\u003e\u003c/sub\u003e: Electron Transfer Rate,\u0026nbsp;\u003cstrong\u003eα\u003c/strong\u003e: Photosynthetic efficiency and\u0026nbsp;\u003cstrong\u003eE\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003ek\u003c/strong\u003e\u003c/sub\u003e: saturation irradiance for the photosynthetic electron transport. Environmental variable,\u0026nbsp;\u003cstrong\u003eSST\u003c/strong\u003e: Sea surface temperature (°C). Illustration\u0026nbsp;\u003cem\u003eM. pyrifera\u003c/em\u003e: Integration and Application Network (http://ian.umces.edu/media-library/)).\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/912b1d3ff992cbbc2d0f4b26.png"},{"id":80828993,"identity":"91f92468-dc7a-4d5b-9e3b-71a7394fe1d6","added_by":"auto","created_at":"2025-04-17 13:47:31","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":749570,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA\u003c/strong\u003e) Seasonal variation in incidence of PAR, UV-A and UV-B radiation for Comau Fjord estimated using the TUV model. \u003cstrong\u003eB\u003c/strong\u003e) Solar spectra measured in autumn 2024 during a light-day cycle (12 hours) outside and inside for Comau Fjord.\u003c/p\u003e","description":"","filename":"FIgure8.png","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/4fcdb3c9e52a746f8f93bbfd.png"},{"id":80831592,"identity":"3ec0570e-6355-43df-ab8e-af99fd9f882c","added_by":"auto","created_at":"2025-04-17 14:11:36","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":16560638,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/bd600019-824c-47ae-8cbf-a18f7e511210.pdf"},{"id":80828511,"identity":"cf866480-b9df-41f4-93ee-3f5cd4513ace","added_by":"auto","created_at":"2025-04-17 13:39:31","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":508513,"visible":true,"origin":"","legend":"","description":"","filename":"Palaciosetal2025Supplementarymaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-6456951/v1/93b18df36ac660b9ed7876e2.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"First photosynthetic characterization of the giant kelp Macrocystis pyrifera from the Comau Fjord, Northern Patagonia region","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe populations of the giant kelp \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (Phaeophyceae, Laminariales) represent the key component of the benthic ecosystems around vast regions along the northern and southern eastern Pacific, south Atlantic coast of Argentina and Malvinas islands, New Zealand, southern Australia, and the sub-Antarctic islands (Huovinen and G\u0026oacute;mez \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Macaya and Zucarello 2010). In the Southern Chilean Patagonia, it is possible to observe extensive and highly productive forests of \u003cem\u003eM. pyrifera\u003c/em\u003e, especially in inlets, channels, and fjords (Dayton \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1985\u003c/span\u003e, Santelices and Ojeda \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e1984\u003c/span\u003ea, b; Friedlander et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2020\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) where they can cover more than 4,840.7 km\u003csup\u003e2\u003c/sup\u003e (Mora-Soto et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Much of the ecological success of \u003cem\u003eM. pyrifera\u003c/em\u003e comes from a remarkable morphological and functional plasticity that allows the species to colonize and dominate in different habitats marked by sharp environmental gradients (Graham et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2007\u003c/span\u003e). A remarkable physiological acclimation to environmental shifts has been commonly reported for populations of the North Pacific coast (Clendennen et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1996\u003c/span\u003e; Cabello-Pasini et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2000\u003c/span\u003e; Umanzor et al. \u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and various sub-Antarctic regions (Cruces et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2012\u003c/span\u003e; Buschmann et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Mabin et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Fern\u0026aacute;ndez et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In this context, the morpho-functional traits of this species, especially its large size and massive canopy structure, determining marked longitudinal gradients in photo-acclimation and photosynthetic performance, are key factors explaining this ecophysiological versatility (Lobban \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; Gerard \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; L\u0026uuml;ning \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; Colombo-Pallota et al. 2006). Thus, giant kelp forests formed by large individuals become a highly complex system on their own, which determines not only its intrinsic patterns in photosynthesis, growth, and productivity but also can buffer the abiotic impacts with significant consequences for the associated marine community (Reed and Foster \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e1984\u003c/span\u003e; Arkema et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). Due to that, the architecture of the kelp forest can vary in response to habitat due to local differences in environmental factors (Stephens et al. \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). It is possible to argue that morpho-functionality, measured as photosynthetic responses, can also vary and thus give insights into the adaptation status of the different giant kelp populations across environmental gradients in extensive geographic areas such as Chilean Patagonia.\u003c/p\u003e \u003cp\u003eThe Comau Fjord (42\u0026deg;22`S), in the northern Patagonian region, comprises 41 km and an average width of 4.5 km with a maximum depth of 500 m (Mayr et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2011\u003c/span\u003e; Huovinen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e) and is considered a unique ecosystem with high primary productivity, high benthic biomass stock, high turnover rates, and high diversity, including abundant presence of rare and threatened species, for example, dense populations of cold-water corals (H\u0026auml;ussermann et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Garcia-Herrera et al. 2020; Beck et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These ecological characteristics, among others, have allowed the establishment of a Marine Protected Area (MPA) of 4.15 km\u003csup\u003e2\u003c/sup\u003e in extension (MPA \u0026ldquo;Fiordo Comau - San Ignacio de Huinay\u0026rdquo;). However, these conservation efforts have not precluded direct and indirect anthropogenic pressures derived mainly from aquaculture activities (especially salmon farming, Buschmann et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2006\u003c/span\u003e), industrial fishing, and climate change (F\u0026ouml;rsterra et al. \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Iriarte \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2018\u003c/span\u003e), generating a 75% loss of species abundance in the last 10 years (Anbleyth-Evans et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn contrast with the southern Patagonian fjords, where \u003cem\u003eM. pyrifera\u003c/em\u003e forms luxuriant forests (Dayton \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Palacios et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Mora-Soto et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), in the estuarine Comau Fjord, marked by a sharp water column stratification due to massive freshwater runoff from rainfall and rivers (Lloncochaigua and Vudodahue rivers) the populations of the giant kelps are scattered in patches through the shallow subtidal between 3 to 6 meters depth (Dayton \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Villalobos et al. \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Due to this, benthic photosynthesis can be possible to have considerable depth as light penetration (PAR) can reach 20 m, but with strong optical stratification (Huovinen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Based on few studies on the marine ecology of this site, has been suggested that the dominance of other conspicuous benthic organisms, e.g. cold-water corals, could substitute the foundational role of giant kelps by modulating the environment, providing a highly complex biogenic habitat and maintaining a distinct self-organized habitat for the associated biota (F\u0026ouml;rsterra et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). However, due to their size and coverage, it is reasonable to argue that the giant kelp is a key species in these environments, thus highlighting the importance of understand its morpho-functionality to define its position in the benthic framework and its contribution to the benthic productivity.\u003c/p\u003e \u003cp\u003eThis study is aimed to characterize for the first time the morphology and photosynthesis of \u003cem\u003eM. pyrifera\u003c/em\u003e from six locations along the Comau Fjord, which will be associated with the local abiotic variables (\u003cem\u003ee.g.\u003c/em\u003e, temperature, light). We address the hypothesis that the environmental settings, especially those associated with the column stratification, can exert a strong impact on the morpho-functionality of \u003cem\u003eM. pyrifera\u003c/em\u003e across a relatively reduced scale. These results are relevant to understand better the status of these populations of \u003cem\u003eM. pyrifera\u003c/em\u003e and their ecosystem functions in an understudied region affected by anthropogenic impacts and to gain insights into the physiological factors underlying the remarkable capacity of this species to thrive across habitats with highly contrasting environmental conditions, especially in one region of Chilean Patagonia cataloged as an area of high value for marine conservation (G\u0026oacute;mez et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) is a global urgency (Arafeh-Dalmau et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), and an area that is being affected by industrial activities that generate a high environmental impact.\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy sites\u003c/h2\u003e \u003cp\u003e \u003cem\u003eM. pyrifera\u003c/em\u003e samples were collected by SCUBA diving in May 2024, during the autumn. Six sites with the presence of \u003cem\u003eM. pyrifera\u003c/em\u003e were selected, distributed along the coast of the Comau Fjord (41 km), considering the oceanic influence from the Pacific to the interior of the fjord where the influence of the Vodudahue River is much more permanent and where they develop in different types of habitats. These \u003cem\u003eM. pyrifera\u003c/em\u003e populations at different sites are subject to dissimilar abiotic conditions (\u003cem\u003ee.g.\u003c/em\u003e, temperature and salinity, Rossbach et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and should exhibit different morphological characteristics and physiological performance (\u003cem\u003ee.g.\u003c/em\u003e, Labb\u0026eacute; et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). Along the Comau Fjord, we identified three areas: 1) Li: Lilihuapi Island, 2) CCh: Cahuelmo Sector and 3) Cf: Inside of the Comau Fjord (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). Also, the subtidal \u003cem\u003eM. pyrifera\u003c/em\u003e assemblages were classified regarding their distribution and coverage into i) \"Patches\" when they correspond to isolated aggregates of \u003cem\u003eM. pyrifera\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB), ii) \"Cordon\" when they are arranged parallel to the coastline (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC) and iii) \"Kelp forests\" when they cover an area larger than 1 hectare (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD). All \u003cem\u003eM. pyrifera\u003c/em\u003e populations along the fjord were settled at different shallow depths between 3 to 5 meters and associated with different habitats (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). Sea surface temperature (SST \u0026deg;C) was estimated using the 4 km and 9 km MODIS L3 layer, which shows nighttime SST, and the 4 km MODIS L3 layer, which shows global daytime sea SST (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://worldview.earthdata.nasa.gov/\u003c/span\u003e\u003cspan address=\"https://worldview.earthdata.nasa.gov/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e, Minnett et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2004\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDescription of the characteristics of the habitat where populations of \u003cem\u003eM. pyrifera\u003c/em\u003e were identified in the inside of the Comau Fjord, Los Lagos region, Chile. Data source for Sea Surface Temperature (SST \u0026deg;C) for the year 2023 (Minnett et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2004\u003c/span\u003e); Salinity (PSU) for 2022 May (Beck et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e); Photosynthetically Active Radiation (PAR) up to 6 meters depth for 2011 February (Laudien et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSites\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLatitud\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eLongitud\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAssociated habitat\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eDepth (m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSST (\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eSalinity (PSU)*\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePAR\u003c/p\u003e \u003cp\u003e[\u0026micro;mol/m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eType of population\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLilihuapi Island\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1-LI\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42\u0026deg;09,35'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u0026deg;35,82'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMytilid kelp paches wall\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e31.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e285.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ePatch\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eCahuelmo Channel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2-CCh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42\u0026deg;14,91'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u0026deg;26,94'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSand and rocks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e31.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eSettled forest\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e3-CCh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42\u0026deg;15,15'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u0026deg;25,30'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eRocks and Boulders\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ePatch\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eComau Fjord\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42\u0026deg;20,64'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u0026deg;27,42'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg; vertical rock wall\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e30.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e194.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eCordon\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42\u0026deg;17,87'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u0026deg;31,16'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg; vertical rock wall\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e30.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eCordon\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e6-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e42\u0026deg;25,97'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e72\u0026deg;25,13'\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eBoulders\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e31.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eCordon\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMorphometric characterization of the thallus\u003c/h3\u003e\n\u003cp\u003eDuring autumn, sporophyte total biomass, total length, stipes numbers (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA\u003cb\u003e.1\u003c/b\u003e), and holdfast maximum height and diameter (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA\u003cb\u003e.2\u003c/b\u003e) of the 126 individuals of \u003cem\u003eM. pyrifera\u003c/em\u003e for each site; 1-LI (n\u0026thinsp;=\u0026thinsp;19), 2-CCh (n\u0026thinsp;=\u0026thinsp;7), 3-CCh (n\u0026thinsp;=\u0026thinsp;21), 4-Cf (n\u0026thinsp;=\u0026thinsp;25), 5-Cf (n\u0026thinsp;=\u0026thinsp;13) and 6-Cf (n\u0026thinsp;=\u0026thinsp;41). At each site, blades of \u003cem\u003eM. pyrifera\u003c/em\u003e were categorized into two zones along the longitudinal profile of the thallus, apical and basal (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA). Additionally, length, width, and area of different blades from each zone were determined to identify morphological differentiation patterns along the fjord (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB). The blade area was estimated by analyzing digital photographs captured with a NIKON D3200 camera in the field on a white surface (contrast), and vectorized using the free ImageJ software (version 1.45, W. Rasband, US National Institutes of Health, Bethesda, Maryland, USA, \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttp://imagej.nih.gov/ij/\u003c/span\u003e\u003cspan address=\"http://imagej.nih.gov/ij/\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eDetermination of solar radiation in underwater light field from Comau Fjord\u003c/h3\u003e\n\u003cp\u003eSeasonal variability for the summer (2023\u0026ndash;2024) and autumn (2024) of UV-B (280\u0026ndash;315 nm), UV-A (315\u0026ndash;400 nm), and photosynthetically active radiation (PAR; 400\u0026ndash;700 nm) at the different sites was estimated using the Tropospheric Ultraviolet and Visible (TUV) Radiation Model (Madronich and Flocke, \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e1999\u003c/span\u003e) (\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://www.acom.ucar.edu/Models/TUV/Interactive_TUV\u003c/span\u003e\u003cspan address=\"https://www.acom.ucar.edu/Models/TUV/Interactive_TUV\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e). To obtain the seasonal values, the maximum value of the day (solar noon) with an ozone layer of 298 DU for autumn and 261 for summer. Measurements were taken every 10 days per month between December 2023 and May 2024. For the calculations, elevation at sea level, low albedo (0.1), typical aerosol profile (standard model configuration), and clear conditions (no clouds) were considered. Measurements were taken every 10 days per month from May 2024 to December 2023. The percentage of radiation attenuation inside the fjord was determined from the database available for the Comau Fjord generated from previous oceanographic campaigns (Laudien et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eChlorophyll fluorescence\u003c/h3\u003e\n\u003cp\u003eThe effective quantum yield of Chl \u003cem\u003ea\u003c/em\u003e fluorescence of photosystem II (Φ\u003csub\u003ePSII\u003c/sub\u003e) was determined \u003cem\u003ein vivo\u003c/em\u003e with a submergible Pulse Amplitude Modulation (PAM) fluorometer (Diving PAM; Walz, Effeltrich, Germany). Measurements were carried out following a longitudinal profile from apical to basal blades. The photosynthetic characteristics of blades from the different sites and depths were determined through photosynthesis vs. irradiance (P-E) curves, based on maximum electron transport rate (ETR\u003csub\u003emax\u003c/sub\u003e), the initial slope indicating the efficiency of photochemistry (α), and the maximal irradiance for ETR saturation (E\u003csub\u003ek\u003c/sub\u003e) using the formula:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:ETR=\\:{{\\Phi\\:}}_{PSII}\\:\\text{x}\\:{E}_{PAR}\\:\\text{x}\\:A\\:\\text{x}\\:{F}_{II}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere Φ\u003csub\u003ePSII\u003c/sub\u003e is the effective quantum yield of fluorescence, E\u003csub\u003ePAR\u003c/sub\u003e is the intensity of the actinic light, A the blade absorptance, and F\u003csub\u003eII\u003c/sub\u003e the fraction of Chl \u003cem\u003ea\u003c/em\u003e associated with the electrons from photosystem II (PSII) to incorporate one CO\u003csub\u003e2\u003c/sub\u003e molecule. In brown macroalgae this value is 0.5 (Grzymski et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e1997\u003c/span\u003e). The absorptance was measured under sunlight by placing the blades (n\u0026thinsp;=\u0026thinsp;12) on a Li-190R quantum sensor (LI-COR Biosciences, Lincoln, NE, USA) according to the formula:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:A=1-T-R$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere T is the transmittance (light transmitted through the blade), and R is the reflectance (reflected fraction).\u003c/p\u003e \u003cp\u003eA nonlinear hyperbolic tangent function (Jassby and Platt \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e1976\u003c/span\u003e) was used to estimate the different photosynthetic parameters:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:ETR=\\:{ETR}_{max}\\:\\text{x}\\text{tanh}(\\alpha\\:\\:\\text{x}\\frac{E}{{ETR}_{max}})$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere ETR\u003csub\u003emax\u003c/sub\u003e is the maximum ETR, tanh is the tangent function, α is the initial slope of the ETR\u0026ndash;E curve. The saturation irradiance for the photosynthetic electron transport (E\u003csub\u003ek\u003c/sub\u003e) was calculated as the intercept between α and ETR\u003csub\u003emax\u003c/sub\u003e.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003eThe differences in blade morphology, and chlorophyll fluorescence based photochemical parameters between populations (LI, CCh and Cf), and blades (apical and basal) were tested using analysis of variance (ANOVA). post hoc analysis (Tukey's HSD) was performed when significant differences were detected (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Assumptions such as homogeneity of variances and normality were examined with Levene and Shapiro-Wilks tests. For non-parametric data, the Kruskal-Wallis tests at a level of significance of α\u0026thinsp;=\u0026thinsp;0.05 were applied. The relationship between multiple physiological and morphological traits (maximum electron transport rate, photosynthetic efficiency, and maximal irradiance for ETR saturation), environmental parameters (water temperature, salinity, type of habitat), and categorical groups (populations type) assessed using Principal Component Analysis (PCA). The factor coordinates of variables and cases, as well as the eigenvalues and variable-factor correlations, were estimated using the means group. Besides, PCA was using the prcomp function (library stats). Figures were generated using the R library \u003cem\u003efactoextra\u003c/em\u003e, and the fviz_pca_var and fviz_pca_biplot functions. All analyzes were performed with the routines defined in the R version 4.4.2 platform (R Core Team \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2024\u003c/span\u003e).\u003c/p\u003e \u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003eSize, Biomass and holdfast of thallus\u003c/h2\u003e \u003cp\u003eSize varied between 0.71 and 3.19 m, with the plants of Lilihuapi Island (1-Li) exhibiting the smallest sizes (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e). The size of the plants shows significant differences between sites, marked by larger population sizes in the Cahuelmo 2 sector (2-CCh) (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The individual wet biomass averaged between 58.95 and 554.70 g (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), with maximum values measured at Cahuelmo 2 (2-CCh) and minima in the Lilihuapi Island (1-Li) (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0003; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). The holdfast was the parameter with the least marked differences between sites (diameter, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0033; height, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0040, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In general, the mean values of maximum holdfast diameter measured did not exceed 3 cm, varying between 1.63 and 2.97 cm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), while holdfast height did not exceed 2 cm, with values between 0.91 and 1.79 cm (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e). In the two parameters the highest measurements were recorded in the Cahuelmo sector (2-CCh) and Comau Fjord 5 (5-Cf). For the number of stipes, the counts do not exceed 4 stipes per plant, with values between 1.95 and 3.71 stipes (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), with significant differences between sites (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0033, Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e) marked by the highest stipe counts in the Cahuelmo sector (2-CCh, 3CCh). Finally, the reproductive status of \u003cem\u003eM. pyrifera\u003c/em\u003e in the different monitoring sites along the Comau Fjord shows a high proportion of reproductive individuals in the sites of Lilihuapi Island (1-Li with 68% reproductive individuals) and sector Cahuelmo 2 (2-CCh with 100% reproductive individuals), which are the populations of \u003cem\u003eM. pyrifera\u003c/em\u003e with more significant influence of the Pacific Ocean (\u003cb\u003eFig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e and \u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e).\u003c/p\u003e \u003cp\u003eThe size distribution of \u003cem\u003eM. pyrifera\u003c/em\u003e along the fjord shows clear segregation concerning the type of population, where the kelp forest in the Cahuelmo 2 sector (2-CCh) shows a greater amount of data in lengths of 3.2 meters, while the populations classified with \"patches\" and \"cords\" the mode of the data are between 0.62 m and 1.75 m (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). The wet biomass distribution shows the same pattern, where the site in the Cahuelmo 2 sector (2-CCh) has the highest biomass observed with 573.9 g, compared to the other sites classified as patches and cordons, where the wet biomass values are between 52.3 g and 72.9 g (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eBlade morphometry\u003c/h3\u003e\n\u003cp\u003eThe blades length, values was \u0026gt;\u0026thinsp;17 cm with obvious differences among sites (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), where the highest values were observed in the sites located in the interior of the Comau Fjord (4-Cf, 5-Cf and 6-Cf), marking significant differences with the other sites (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001; Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). As for the width of the blades, the values varied between 3.43 and 8.48 cm (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e), showing significant differences between sites (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001), which were grouped into three groups, with the lowest values recorded on Lilihuapi Island (1-Li), the average values in the Cahuelmo sector (2-CCh and 3-CCh) and the interior of the Comau Fjord (4-Cf, 5-Cf and 6-Cf) showed the widest leaves (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). In the case of blades area, the mean ranged from 40.6 to 211.0 cm\u003csup\u003e2\u003c/sup\u003e (\u003cb\u003eTable \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u003c/b\u003e) with significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001) between sites and repeating the same pattern observed for blades width (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC and Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Likewise, no differences in morphological features were observed in the apical and basal blades at sites 1-Li, 2 CCh and 3 CCh, a situation different from that recorded for the sites located inside the Comau Fjord (4-Cf, 5-Cf and 6-Cf) (\u003cb\u003eTable S2\u003c/b\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResults of analysis of variance (ANOVA) for comparisons between sampling \u003cb\u003esites\u003c/b\u003e considering morphometry of thallus and blades (n\u0026thinsp;=\u0026thinsp;126 plant; n\u0026thinsp;=\u0026thinsp;196 blades) of \u003cem\u003eM. pyrifera\u003c/em\u003e in the Comau Fjord. The results of one-way ANOVA and Kruskal-Wallis tests for non-parametric data are included (α\u0026thinsp;=\u0026thinsp;0.05). *DF degrees of freedom, SE standard error, MS mean squares, F F statistic; P values in bold indicate significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eANOVA\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVariable\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePr(\u0026gt;\u0026thinsp;F)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePlant size\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.2458\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2551\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.219\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eWet biomass\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.4918\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1735\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.037\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0003\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBlade length\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e186\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1739\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.2152\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e10.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eArea blades\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e186\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.2530\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4603\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e31.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eKruskal-Wallis test\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eVariable\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChi\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePr(\u0026gt;\u0026thinsp;F)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eHoldfast diameter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17.766\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0033\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eHoldfast height\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17.766\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0040\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eStipe number\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e17.723\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0033\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eBlade width\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e91.918\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eChlorophyll florescence-based photosynthesis\u003c/h2\u003e \u003cp\u003ePhotochemical profiles determined in different populations along the Comau Fjord showed shade adapted characteristics. Ф\u003csub\u003ePSII\u003c/sub\u003e varied between 0.39 in algae from Comau Fjord 6 (6-Cf) and 0.57 in the population of Comau sector 3 (3-CCh) with significant differences between all sites (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.03) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). At the level of lamina type, significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) are observed in 4 sites (1-Li, 2-CCh, 3-CCh and 4-Cf), but without clear patterns with respect to apical and basal laminae. While for the sites located at the head of the Comau Fjord (5-Cf and 6-Cf) no significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) in this photochemical parameter are evident (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). For ETR\u003csub\u003emax\u003c/sub\u003e a mean of 30.73 [\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e] was obtained for all sites, however, in the interior of Comau Fjord 6 (6-Cf) showed significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.0001) with respect to the other sites with lower values. Values for this photosynthetic parameter ranged from 17.34 to 45.06 [\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e] (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eA and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The photosynthetic efficiency, estimated as α, averaged 0.41 [\u0026micro;mol e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e] [\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003csup\u003e\u0026minus;1\u003c/sup\u003e for all sites, however, in Comau Fjord 4 inside (4-Cf) it was lower than in rest of the sites no significant differences were observed in this parameter (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.1316), where values varied between 0.33 and 0.51 [\u0026micro;mol e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e] [\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003csup\u003e\u0026minus;1\u003c/sup\u003e(Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eB and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). In the case of saturating irradiances (E\u003csub\u003ek\u003c/sub\u003e), the values reached an average of 86.94 (\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), with significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0062) between the three sectors of the Comau Fjord (Lilihuapi Island, Cahuelmo sector and Inside the Comau Fjord). The highest observed E\u003csub\u003ek\u003c/sub\u003e values were recorded in the Cahuelmo sector (2-CCh and 3-CCh) and the first point inside Comau Fjord 4 (4-Cf), and the lowest records of photochemistry saturation in algae at points 5 and 6 inside Comau Fjord (5-Cf\u0026thinsp;=\u0026thinsp;62.04 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; 6-Cf\u0026thinsp;=\u0026thinsp;59.54\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eC and Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eFluorescence-based photochemical characterization of \u003cem\u003eM. pyrifera\u003c/em\u003e across different sites and blade types (apical and basal) along a Comau Fjord. Effective quantum yield (Φ\u003csub\u003ePSII\u003c/sub\u003e) was measured in situ using a Diving-PAM for a total of \u003cb\u003e96 blades\u003c/b\u003e. ETR-based P-E curve parameters (ETR\u003csub\u003emax\u003c/sub\u003e, α and E\u003csub\u003ek\u003c/sub\u003e) correspond to mean values\u0026thinsp;\u0026plusmn;\u0026thinsp;CI (n\u0026thinsp;=\u0026thinsp;8). Abbreviations: Lilihuapi Island (\u003cb\u003e1-Li\u003c/b\u003e), Cahuelmo sector (\u003cb\u003e2-CCh\u003c/b\u003e, \u003cb\u003e3-CCh\u003c/b\u003e), Comau Fjord inside (\u003cb\u003e4-Cf\u003c/b\u003e, \u003cb\u003e5-Cf\u003c/b\u003e and \u003cb\u003e6-Cf\u003c/b\u003e). Different letters denote significant mean differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) according to post hoc Tukey's HSD test.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"8\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSites\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eEffective quantum yield\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c6\" namest=\"c3\"\u003e \u003cp\u003eP-E curve parameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eETR\u003csub\u003emax\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eα\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eE\u003csub\u003ek\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(Ф\u003csub\u003ePSII\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e(\u0026micro;mol e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e[\u0026micro;mol e\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e] [\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003csup\u003e\u0026minus;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e(\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-Li\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.52\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e32.04\u0026thinsp;\u0026plusmn;\u0026thinsp;4.87 (a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.51\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e67.11\u0026thinsp;\u0026plusmn;\u0026thinsp;21.91(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-CCh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e42.61\u0026thinsp;\u0026plusmn;\u0026thinsp;11.88(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e122.69\u0026thinsp;\u0026plusmn;\u0026thinsp;35.66(a,b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-CCh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.57\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08(a,b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e45.06\u0026thinsp;\u0026plusmn;\u0026thinsp;10.68(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.04(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e104.54\u0026thinsp;\u0026plusmn;\u0026thinsp;17.68(a,c)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e24.38\u0026thinsp;\u0026plusmn;\u0026thinsp;5.20(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.33\u0026thinsp;\u0026plusmn;\u0026thinsp;0.14(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e105.74\u0026thinsp;\u0026plusmn;\u0026thinsp;67.24(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.53\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e22.97\u0026thinsp;\u0026plusmn;\u0026thinsp;9.32(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.48\u0026thinsp;\u0026plusmn;\u0026thinsp;0.20(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e62.04\u0026thinsp;\u0026plusmn;\u0026thinsp;44.79(a,c)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.38\u0026thinsp;\u0026plusmn;\u0026thinsp;0.09(a,c)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003e17.34\u0026thinsp;\u0026plusmn;\u0026thinsp;3.13(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.36\u0026thinsp;\u0026plusmn;\u0026thinsp;0.22(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003e59.54\u0026thinsp;\u0026plusmn;\u0026thinsp;28.35(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBlades type\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"6\" morerows=\"1\" nameend=\"c7\" namest=\"c2\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eSites\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e(Ф\u003csub\u003ePSII\u003c/sub\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"1\" nameend=\"c8\" namest=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e1-Li\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cb\u003e2-CCh\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u003cb\u003e3-CCh\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u003cb\u003e4-Cf\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e5-Cf\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cb\u003e6-Cf\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eApical\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.63\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.39\u0026thinsp;\u0026plusmn;\u0026thinsp;0.08(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.72\u0026thinsp;\u0026plusmn;\u0026thinsp;0.13(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.50\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.41\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBasal\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.45\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.46\u0026thinsp;\u0026plusmn;\u0026thinsp;0.10(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.40\u0026thinsp;\u0026plusmn;\u0026thinsp;0.07(b)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.56\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.35\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11(a)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIn situ irradiance (\u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003es\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e96.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e357.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e782.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e178.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e430.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e435.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eResults of analysis of variance (ANOVA) for comparisons between sampling (\u003cb\u003eA\u003c/b\u003e) sites considering physiological characteristics and (\u003cb\u003eB\u003c/b\u003e) blade type (apical and basal) of \u003cem\u003eM. pyrifera\u003c/em\u003e in the Comau Fjord (n\u0026thinsp;=\u0026thinsp;8). The results of one-way ANOVA and Kruskal-Wallis tests for non-parametric data are included (α\u0026thinsp;=\u0026thinsp;0.05). *DF degrees of freedom, SE standard error, MS mean squares, F F statistic; P values in bold indicate significant differences (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eANOVA\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e(A)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePr(\u0026gt;\u0026thinsp;F)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eETR\u003csub\u003emax\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1455\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5151\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e9.348\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eα\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1487\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.1702\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.805\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.1316\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eE\u003csub\u003ek\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.2249\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.3002\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e3.776\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0062\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eKruskal-Wallis test\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChi\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePr(\u0026gt;\u0026thinsp;F)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eФ \u003csub\u003ePSII\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e12.264\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0314\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003e(B)\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eANOVA\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eSites\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSE\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePr(\u0026gt;\u0026thinsp;F)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2-CCh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1648\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.5225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e30.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e\u0026lt;\u0026thinsp;0.0001\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e4-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.1278\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.4981\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e15.88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0011\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e6-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.2239\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.0166\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.3904\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.5383\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c6\" namest=\"c2\"\u003e \u003cp\u003eKruskal-Wallis test\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eDF\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eChi\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePr(\u0026gt;\u0026thinsp;F)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1-Li\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e4.9703\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0258\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3-CCh\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8.7518\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u003cb\u003e0.0031\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e5-Cf\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1.2601\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.2616\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eMultivariate analysis\u003c/h2\u003e \u003cp\u003ePCA indicated that dimension 1 accounted for 46.4% of the variability, while dimension 2 accounted for 21.7%. Together, both components accounted for 68.1% of the total variability of all variables studied (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). Overall, correlations for the two dimensions discriminated between variables associated with blades morphology and variables related to photobiological characteristics for each site in Comau Fjord (\u003cb\u003eFig. S2\u003c/b\u003e). PC1 was mainly related to the variability of sites located in the inside Comau Fjord (4-CCh, 5-CCh, 6-CCh), defined by a higher contribution of blades morphological variables and a decrease in effective quantum yield (Ф\u003csub\u003ePSII\u003c/sub\u003e) (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cb\u003eFig. S2\u003c/b\u003e). PC2 defined the variability associated with \u003cem\u003eM. pyrifera\u003c/em\u003e populations located at the entrance of the Comau Fjord (1-Li, 2-CCh, 3CCh). Here, higher contributions were observed for physiological variables (ETR\u003csub\u003emax\u003c/sub\u003e, E\u003csub\u003ek\u003c/sub\u003e, and α), mean annual sea surface temperature (SST\u0026deg;C), and higher holdfast diameter values defined the component (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e and \u003cb\u003eFig. S2\u003c/b\u003e). Grouping the information by population type, we can observe that PC2 is related to \u0026ldquo;kelp forests\u0026rdquo; and \u0026ldquo;patch\u0026rdquo; where the physiological variables, in addition to the distribution of thallus morphological variables, especially for site 2-CCh (see Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, \u0026ldquo;kelp forests\u0026rdquo;) show a more significant contribution. In contrast, PC1 is related exclusively to populations of \u003cem\u003eM. pyrifera\u003c/em\u003e that are distributed in the form of a \u0026ldquo;cordon\u0026rdquo; where the increase in the values of the morphological variables of the blades shows a strong contribution (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eGiant kelp morphology of the Comau Fjord\u003c/h2\u003e \u003cp\u003eIn the present study, several indicators based on morphological traits of \u003cem\u003eM. pyrifera\u003c/em\u003e (\u003cem\u003ee.g.\u003c/em\u003e, thallu size and wet biomass) did not reveal marked differences between populations when values were analyzed at the organism level, with the exception of the population present in sector 2 of Cahulemo (2-CCh) which was the only site where a population with a well recognizable \u0026ldquo;kelp forest\u0026rdquo; structure was identified (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). However, morphometric variables of blades and physiological indicators (\u003cem\u003ee.g.\u003c/em\u003e, ETR\u003csub\u003emax\u003c/sub\u003e, α and E\u003csub\u003ek\u003c/sub\u003e), correlated to different degrees with the type of \u003cem\u003eM. pyrifera\u003c/em\u003e population present along the Comau Fjord (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). This is especially evident in the segregation observed between the populations located inside the Comau Fjord (sites 4, 5 and 6) and those present at its mouth (Lilihuapi Island and Cahuelmo sector), which show clear differences linked to physiological traits and morphometric characteristics of the blades such as length, width and area (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). To understand these observed patterns, it is necessary to understand the dynamics of variation of abiotic factors that occur within the Comau Fjord. In this sense, several studies have reported that the geomorphology of the fjord, with an extension of 41 km, shows a marked stratification of the water column in terms of salinity, temperature and PAR (Jantzen et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Huovinen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Laudien et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Villalobos et al. \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Rossbach et al. \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Beck et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). These strong variation along the fjord have been attributed to the macromareal environment of the fjord with tidal ranges of up to 7.5 m (H\u0026auml;ussermann and F\u0026ouml;rsterra \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2009\u003c/span\u003e), which are intensified by strong annual fluctuations in position and intensity of solar radiation cycles, precipitation, and tidal mixing (F\u0026ouml;rsterra \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2009\u003c/span\u003e; Sobarzo-Bustamante \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e2009\u003c/span\u003e). In terms of adaptive strategy, as observed in Southern Patagonia (Huovinen et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Palacios et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), these populations of the giant kelp \u003cem\u003eM. pyrifera\u003c/em\u003e have developed morphofunctional responses, such as increasing the area of absorption of solar radiation (\u003cem\u003ee.g.\u003c/em\u003e, increasing the surface area of its blades), which allows it to withstand local and seasonal changes in environmental conditions along the Comau Fjord. Along these lines, such \u003cem\u003eM. pyrifera\u003c/em\u003e populations, which withstand variations in abiotic conditions in the water column at different spatio-temporal scales, depend on the optical characteristics of the water (G\u0026oacute;mez et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2005\u003c/span\u003e) that in turn, influence the availability of light for photosynthesis (Huovinen et al. 2011). This is reflected along the Comau Fjord, differentiating those populations present in the Lilihuapi Island and Cahuelmo sector from those located inland, and which can adjust morphological traits and physiological responses to cope with daily and seasonal variations in light and nutrients (Kaminsky et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2024\u003c/span\u003e), allowing it to minimize physiological damage like other populations of \u003cem\u003eM. pyrifera\u003c/em\u003e studied in fjords of southern Patagonia (Palacios et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Coral-Santacruz et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). At the same time have confirmed that the blades of \u003cem\u003eM. pyrifera\u003c/em\u003e possess adaptive strategies in response to the conditions of their environment; for example, blades that are located on the surface are better adapted to a high-light environment, and those located in deeper areas are better adapted to a low light environment presenting dynamic photoinhibition of photosynthesis during midday and recovery of photosynthesis during the afternoon and/or evening (Buschmann et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). These blade qualities determine the demographic structure and architectural characteristics of \u003cem\u003eM. pyrifera\u003c/em\u003e populations in response to the combination of internal factors and the impact of abiotic and biotic factors on specific traits (Layton et al., \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cb\u003ePhotobiological traits of\u003c/b\u003e \u003cb\u003eM. pyrifera\u003c/b\u003e: \u003cb\u003eimplications for functional local adaptation of plants across Comau Fjord\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe absorption of solar radiation by \u003cem\u003eM. pyrifera\u003c/em\u003e takes place in its fronds, and its degree of efficiency is based, firstly, on the ability to harness that radiation, turning these macroalgae into black objects that absorb practically the entire spectrum of incident light in the water column (Lobban \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e1978\u003c/span\u003e; L\u0026uuml;ning \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e1990\u003c/span\u003e). Second, a canopy structure organized in a multilayered frond system, which is morphologically and functionally analogous to the leaves of higher plants, thus representing structures highly specialized in light absorption. These qualities are key in an environment where seasonal variations in the incidence of solar radiation are as accentuated as those observed in Comau Fjord. Our analysis confirms that solar radiation from summer to autumn has a marked decrease in the whole area (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eA), a stress factor that these populations of \u003cem\u003eM. pyrifera\u003c/em\u003e must face during an annual cycle.\u003c/p\u003e \u003cp\u003eThe most striking photobiological feature in the \u003cem\u003eM. pyrifera\u003c/em\u003e populations studied along the Comau Fjord was the low light requirement for photochemistry, indicating an adaptation to shade. Considering the geomorphological context of the fjord, that is marked by a strong light restriction due to the obstruction of solar radiation by the surrounding mountain ranges (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003eB) which causing a direct attenuation of solar radiation of ~\u0026thinsp;32% (\u003cb\u003eTable S3\u003c/b\u003e), the algae show some general patterns: (a) photochemical efficiency (α) and effective quantum yield (Ф\u003csub\u003ePSII\u003c/sub\u003e), did not vary significantly between sites; (b) ETR\u003csub\u003emax\u003c/sub\u003e and E\u003csub\u003ek\u003c/sub\u003e values were relatively higher in the algae of located at the mouth of the Comau Fjord (Lilihuapi Island and Cahuelmo sector), compared to the other sites located inside the fjord (4-Cf, 5-Cf, and 6-Cf). These results suggest site-dependent differences, mainly associated with the degree of exposure of the blades to solar radiation.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eHowever, when considering the types of blades along a depth gradient, no marked differences were found, except for the light requirements (E\u003csub\u003ek\u003c/sub\u003e) in the populations distributed inside the Comau Fjord (5-Cf and 6-Cf), whose values were higher in the apical blades (\u003cb\u003eFig. S2\u003c/b\u003e and \u003cb\u003eTable S4\u003c/b\u003e). Unlike populations measured in the Strait of Magellan (Puerto del Hambre; Marambio et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2017\u003c/span\u003e) and in the Beagle Channel (Yendegaia Fjord; Palacios et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), where \u003cem\u003eM. pyrifera\u003c/em\u003e specimens exceed 15 m in length, the photobiological differences in the blades at the vertical level are evident and respond to a strategy of use of solar radiation along the water column. In contrast to what was observed in the Comau Fjord, the average length of \u003cem\u003eM. pyrifera\u003c/em\u003e specimens did not exceed 1.5 m; apparently, adaptation to shade is a response of these populations that during the winter period must respond to low light conditions. The limited physiological studies carried out on populations of \u003cem\u003eM. pyrifera\u003c/em\u003e in Northern Patagonia limit to establish with certainty how the photochemical responses of this type of macroalgae operate, even more so in the absence of seasonal studies. However, in other areas of southern Patagonia, some antecedents reveal that this species presents putative photochemical adaptations to cope with low light (Marambio et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Ziemmann dos Santos et al. 2019), apparently constitutive and that for \u003cem\u003eM. pyrifera\u003c/em\u003e populations in Comau Fjord, it could be the response mechanism to light limitation during pre-winter periods and where solar radiation winter penetration levels have already been characterized with attenuation coefficients (K\u003csub\u003edpar\u003c/sub\u003e) of 0.67 m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and Z\u003csub\u003e1%\u003c/sub\u003e reaching depths of 3.5 m (Huovinen et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Light requirements for photochemical saturation\u0026thinsp;\u0026lt;\u0026thinsp;50 \u0026micro;mol m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are common for \u003cem\u003eM. pyrifera\u003c/em\u003e (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), suggesting that this species adjusts light use to much lower levels than those existing in the field. This pattern resembles adaptations found in large Antarctic brown algae (Huovinen and G\u0026oacute;mez \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; G\u0026oacute;mez et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Adaptation to shade may be functional to cope not only with limited light during prolonged winter at high latitudes, during episodes of increased light attenuation due to sedimentation caused by storms or currents but also confer photobiological capabilities to extend the range to deeper locations (G\u0026oacute;mez et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; G\u0026oacute;mez and Huovinen \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2015\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThis type of study, which characterizes for the first time the morphology and physiology of these natural populations of \u003cem\u003eM. pyrifera\u003c/em\u003e, allows us to understand how the patterns of distribution and demographic structuring in response to dynamic change factors in northern Patagonia are and will be in the future. Furthermore, they reaffirm the importance of continuing to gather information at a broader spatio-temporal scale that allows us to understand how stressors condition the ecophysiology of these \u003cem\u003eM. pyrifera\u003c/em\u003e populations in a region that is suffering the consequences of global climate change, such as Northern Patagonia, and that is also intensely impacted by local anthropogenic activities.\u003c/p\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThis work was made possible by Fundaci\u0026oacute;n Rewilding Chile, a Chilean non-profit financially supported by an extensive philanthropic network and the FONDAP IDEAL Center [Grant 15150003]; Fondecyt Proyect [Grant 1241571] awarded to IG.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eM.P.: Writing-original draft, Conceptualization, Investigation/bibliographic research, Methodology, Formal analysis, Review and editing. M.H.: Review and editing, Supervision, Resources, Funding acquisition, Project administration. I.G.: Methodology, Review and Editing, Resources.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe greatly appreciate the in-situ logistic support of the Fundaci\u0026oacute;n Rewilding Chile during our fieldwork in the Comau Fjord, in particular from team members J. Poblete, J.L. Kappes and J.T. Yakasovic.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnbleyth-Evans J, Araos-Leiva F, Ther R\u0026iacute;os F, Segovia-Cort\u0026eacute;s R, H\u0026auml;ussermann V, Aguirre-Mu\u0026ntilde;oz C (2020). Toward marine democracy in Chile: Examining aquaculture ecological impacts through common property local ecological knowledge. Mar Policy 113: 103690. https://doi.org/10.1016/j.marpol.2019.103690\u003c/li\u003e\n\u003cli\u003eArafeh-Dalmau N, Olgun-Jacobson C, Earle S, Bello M, Lagger C, Mora-Soto A, Pantano C, Palacios M, et al. (2024). Protect kelp forests. Science 386: 629-629. https://doi.org/10.1126/science.adr4814\u003c/li\u003e\n\u003cli\u003eArkema KK, Reed DC, Schroeter SC (2009). Direct and indirect effects of giant kelp determine benthic community structure and dynamics. Ecology 90: 3126-3137. https://doi.org/10.1890/08-1213.1\u003c/li\u003e\n\u003cli\u003eBeck KK, Schmidt-Grieb GM, Laudien J, et al. (2022). Environmental stability and phenotypic plasticity benefit the cold-water coral \u003cem\u003eDesmophyllum dianthus\u003c/em\u003e in an acidified fjord. Commun Biol 5: 683. https://doi.org/10.1038/s42003-022-03622-3\u003c/li\u003e\n\u003cli\u003eBuschmann AH, Pereda SV, Varela DA, Rodr\u0026iacute;guez-Maul\u0026eacute;n J, L\u0026oacute;pez A, Gonz\u0026aacute;lez-Carvajal L, et al. (2014). Ecophysiological plasticity of annual populations of giant kelp (\u003cem\u003eMacrocystis pyrifera\u003c/em\u003e) in a seasonally variable coastal environment in the Northern Patagonian Inner Seas of Southern Chile. J Appl Phycol 26: 837-847. https://doi.org/10.1007/s10811-013-0070-z\u003c/li\u003e\n\u003cli\u003eBuschmann AH, Riquelme VA, Hern\u0026aacute;ndez-Gonz\u0026aacute;lez MC, Varela D, Jim\u0026eacute;nez JE, Henr\u0026iacute;quez LA, Vergara PA, Gu\u0026iacute;\u0026ntilde;ez R, Fil\u0026uacute;n L (2006). A review of the impacts of salmonid farming on marine coastal ecosystems in the southeast Pacific. ICES J Mar Sci 63 (7): 1338-1345. https://doi.org/10.1016/j.icesjms.2006.04.021\u003c/li\u003e\n\u003cli\u003eCabello-Pasini A, Aguirre-von-Wobeser E, Figueroa FL (2000). Photoinhibition of photosynthesis in \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (Phaeophyceae), \u003cem\u003eChondrus crispus\u003c/em\u003e (Rhodophyceae) and \u003cem\u003eUlva lactuca\u003c/em\u003e (Chlorophyceae) in outdoor culture systems. J Photochem Photobiol B Biol 57: 169-78. https://doi.org/10.1016/S1011-1344(00)00095-6\u003c/li\u003e\n\u003cli\u003eClendennen SK, Zimmerman RC, Powers DA, Alberte RS (1996). Photosynthetic response of the giant kelp \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (Phaeophyceae) to ultraviolet radiation. J Phycol 32: 614-620. https://doi.org/10.1111/j.0022-3646.1996.00614.x\u003c/li\u003e\n\u003cli\u003eColombo-Pallotta MF, Garc\u0026iacute;a-Mendoza E, Ladah LB (2006). Photosynthetic performance, light absorption, and pigment composition of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (Laminariales, Phaeophyceae) blades from different depths. J Phycol 42: 1225-1234. https://doi.org/10.1111/j.1529-8817.2006.00287.x\u003c/li\u003e\n\u003cli\u003eCoral-Santacruz D, M\u0026eacute;ndez F, Marambio J, et al. (2024). Effects of glacial melting on physiological performance of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e in the Fjord of the Mountains, Magellanic Sub-Antarctic ecoregion, Chile. J Appl Phycol 36: 3637-3648. https://doi.org/10.1007/s10811-024-03362-3\u003c/li\u003e\n\u003cli\u003eCruces E, Huovinen P, G\u0026oacute;mez I (2012). Phlorotannin and antioxidant responses upon short-term exposure to UV radiation and elevated temperature in three South Pacific kelps. Photochem Photobiol 88: 58-66. https://doi.org/10.1111/j.1751-1097.2011.01013.x\u003c/li\u003e\n\u003cli\u003eDayton PK (1985). The structure and regulation of some South American kelp communities. Ecol Monogr 55: 447-468.\u003c/li\u003e\n\u003cli\u003eFern\u0026aacute;ndez PA, Navarro JM, Camus C, et al. (2021). Effect of environmental history on the habitat-forming kelp \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e responses to ocean acidification and warming: a physiological and molecular approach. Sci Rep 11: 2510. https://doi.org/10.1038/s41598-021-82094-7\u003c/li\u003e\n\u003cli\u003eF\u0026ouml;rsterra G, H\u0026auml;ussermann V, Laudien J (2017). Animal forests in the Chilean fjords: Discoveries, Perspectives and Threats in Shallow and Deep Waters. In: Rossi S, Bramanti L, Gori A, Orejas Saco del Valle C (Eds) Marine Animal Forests: The Ecology of Benthic Biodiversity Hotspots. Springer International Publishing 277\u0026ndash;313. https://doi.org/10.1007/978-3-319-21012-4_3\u003c/li\u003e\n\u003cli\u003eF\u0026ouml;rsterra G, H\u0026auml;ussermann V, Laudien J (2016). Animal Forests in the Chilean Fjords: Discoveries, Perspectives and Threats in Shallow and Deep Waters. In: Rossi S, Bramanti L, Gori A, Orejas Saco del Valle C (Eds) Marine Animal Forests Springer, Cham. https://doi.org/10.1007/978-3-319-17001-5_3-1\u003c/li\u003e\n\u003cli\u003eF\u0026ouml;rsterra G (2009). Ecological and biogeographical aspects of the Chilean fjord region. In: H\u0026auml;ussermann V, F\u0026ouml;rsterra G (Eds) Marine Benthic Fauna of Chilean Patagonia (Santiago: Nature In focus), 61-76.\u003c/li\u003e\n\u003cli\u003eFriedlander AM, Ballesteros E, Goodell W, H\u0026uuml;ne M, Mu\u0026ntilde;oz A, Salinas-de-Le\u0026oacute;n P, et al. (2021). Marine communities of the newly created Kaw\u0026eacute;sqar National Reserve, Chile: From glaciers to the Pacific Ocean. PLoS One 16(4): e0249413. https://doi.org/10.1371/journal.pone.0249413\u003c/li\u003e\n\u003cli\u003eFriedlander AM, Ballesteros E, Bell TW, Caselle JE, Campagna C, Goodell W, et al. (2020). Kelp forests at the end of the earth: 45 years later. PLoS One. 15: e0229259. https://doi.org/10.1371/journal.pone.0229259\u003c/li\u003e\n\u003cli\u003eGarcia-Herrera N, Cornil A, Laudien J, Niehoff B, H\u0026ouml;fer J, F\u0026ouml;rsterra G, Richter C (2022). Seasonal and diel variations in the vertical distribution, composition, abundance and biomass of zooplankton in a deep Chilean Patagonian Fjord. PeerJ 10: e12823. https://doi.org/10.7717/peerj.12823\u003c/li\u003e\n\u003cli\u003eGerard VA, 1986. Photosynthetic characteristics of giant kelp (\u003cem\u003eMacrocystis pyrifera\u003c/em\u003e) determined in situ. Mar Biol 90: 473-482.\u003c/li\u003e\n\u003cli\u003eG\u0026oacute;mez I, Garc\u0026eacute;s-Vargas J, Garrido I, Huovinen P, Macaya E, Mellado MA, Navarro NP, Palacios M, Pardo LM, Soto D, Valdivia N, Navarro A (2024). Bosques Submarinos de la Patagonia. ISBN 978-956-418-537-8, 139 pp.\u003c/li\u003e\n\u003cli\u003eG\u0026oacute;mez I, Navarro NP, Huovinen P (2019). Bio-optical and physiological patterns in Antarctic seaweeds: a functional trait based approach to characterize vertical zonation Prog Oceanogr 174: 17-27 https://doi.org/10.1016/j.pocean.2018.03.013\u003c/li\u003e\n\u003cli\u003eG\u0026oacute;mez I, Huovinen P (2015). Lack of physiological depth patterns in conspecifics of endemic Antarctic brown algae: A trade-off between UV stress tolerance and shade adaptation?. PLoS ONE 10(8): e0134440. https://doi.org/10.1371/journal.pone.0134440\u003c/li\u003e\n\u003cli\u003eG\u0026oacute;mez I, Figueroa FL, Huovinen P, Ulloa N, Morales V (2005). Photosynthesis of the red alga \u003cem\u003eGracilaria chilensis\u003c/em\u003e under natural solar radiation in an estuary in southern Chile. Aquaculture 244 (1-4): 369-382. https://doi.org/10.1016/j.aquaculture.2004.11.037\u003c/li\u003e\n\u003cli\u003eG\u0026oacute;mez I, Weykam G, Kl\u0026ouml;ser H, Wiencke C (1997). Photosynthetic light requirements, metabolic carbon balance and zonation of sublittoral macroalgae from King George Island (Antarctica). Mar Ecol Prog Ser 149: 281-293.\u003c/li\u003e\n\u003cli\u003eGraham MH, Vasquez JA, Buschmann AH (2007). Global ecology of the giant kelp \u003cem\u003eMacrocystis\u003c/em\u003e. Oceanogr. Mar Biol Annu Rev 45: 39-88.\u003c/li\u003e\n\u003cli\u003eGrzymski J, Johnsen G, Sakshaug E (1997). The significance of intracellular self-shading on the biooptical properties of brown, red, and green macroalgae. J Phycol 33: 408-414. https://doi.org/10.1111/j.0022-3646.1997.00408.x\u003c/li\u003e\n\u003cli\u003eH\u0026auml;ussermann V, F\u0026ouml;rsterra G, Melzer RR, Meyer R (2013). Gradual changes of benthic biodiversity in Comau Fjord, Chilean Patagonia \u0026ndash; lateral observations over a decade of taxonomic research. Spixiana 36 (2): 161-171\u003c/li\u003e\n\u003cli\u003eH\u0026auml;ussermann V, F\u0026ouml;rsterra G (2009). Marine Benthic Fauna of Chilean Patagonia: Illustrated Identification Guide. Santiago: Nature in Focus.\u003c/li\u003e\n\u003cli\u003eHuovinen P, Ram\u0026iacute;rez J, Palacios M, G\u0026oacute;mez I (2020). Satellite-derived mapping of kelp distribution and water optics in the glacier impacted Yendegaia Fjord (Beagle Channel, Southern Chilean Patagonia). Sci Total Environ 703: 135531. https://doi.org/10.1016/j.scitotenv.2019.135531\u003c/li\u003e\n\u003cli\u003eHuovinen P, Ram\u0026iacute;rez J, G\u0026oacute;mez I (2016). Underwater Optics in Sub-Antarctic and Antarctic Coastal Ecosystems. PLoS ONE 11(5): e0154887. https://doi.org/10.1371/journal.pone.0154887\u003c/li\u003e\n\u003cli\u003eHuovinen P, G\u0026oacute;mez I (2013). Photosynthetic characteristics and UV stress tolerance of Antarctic seaweeds along the depth gradient. Polar Biol 36: 1319-1332. https://doi.org/10.1007/s00300-013-1351-3\u003c/li\u003e\n\u003cli\u003eHuovinen P, G\u0026oacute;mez I (2012). Cold-temperate seaweeds communities of the southern Hemisphere. In: Wiencke C, Bischof K (Eds) Seaweed Biology: Novel Insights into Ecophysiology, Ecology and Utilization (219) Ecological Studies, Springer. pp 293-313. https://doi.org/10.1007/978-3-642-28451-9_14\u003c/li\u003e\n\u003cli\u003eHuovinen P, G\u0026oacute;mez I (2011). Spectral attenuation of solar radiation in Patagonian fjords and coastal waters and implications for algal photobiology. Cont Shelf Res 31: 254-259. https://doi.org/10.1016/j.csr.2010.09.004\u003c/li\u003e\n\u003cli\u003eIriarte JL (2018). Natural and human influences on marine processes in Patagonian subantarctic coastal waters. Front Mar Sci 5: 360. https://doi.org/10.3389/fmars.2018.00360\u003c/li\u003e\n\u003cli\u003eJantzen C, Laudien J, Sokol S, F\u0026ouml;rsterra G, H\u0026auml;ussermann V, Kupprat F, et al. (2013). In situ short-term growth rates of a cold-water coral. Mar Freshw Res 64: 631\u0026ndash;641. https://doi.org/10.1071/MF12200\u003c/li\u003e\n\u003cli\u003eJassby AD, Platt T (1976). Mathematical formulation of the relationship between photosynthesis and light for phytoplankton. Limnol Oceanogr 21: 540-547.\u003c/li\u003e\n\u003cli\u003eKaminsky J, Bagur M, Schloss IR, et al. (2024). Giant kelp (\u003cem\u003eMacrocystis pyrifera\u003c/em\u003e) morphological and reproductive strategies in two contrasting sub-Antarctic forests. Mar Biol 171: 9. https://doi.org/10.1007/s00227-023-04341-x\u003c/li\u003e\n\u003cli\u003eLaudien J, Jantzen C, H\u0026auml;ussermann V, F\u0026ouml;rsterra G, Sswat M, Baumgarten S, Richter C (2017). Physical oceanographic profiles of seven CTD casts from Gulf of Ancud into Comau Fjord in 2011 [dataset]. Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, PANGAEA, https://doi.org/10.1594/PANGAEA.884120\u003c/li\u003e\n\u003cli\u003eLabb\u0026eacute; BS, Fern\u0026aacute;ndez PA, Florez JZ, Buschmann AH (2024). Effects of pH, Temperature, and Light on the Inorganic Carbon Uptake Strategies in Early Life Stages of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (Ochrophyta, Laminariales). Plants 13: 3267. https://doi.org/10.3390/plants13233267\u003c/li\u003e\n\u003cli\u003eLayton C, Shelamoff V, Cameron MJ, Tatsumi M, Wright JT, Johnson CR (2019). Resilience and stability of kelp forests: The importance of patch dynamics and environment-engineer feedbacks. PLoS One. 14(1): e0210220. https://doi.org/10.1371/journal.pone.0210220\u003c/li\u003e\n\u003cli\u003eLobban CS (1978). Translocation of 14C in \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (giant kelp). Plant Physiol 61: 585-589. https://doi.org/10.1104/pp.61.4.585\u003c/li\u003e\n\u003cli\u003eL\u0026uuml;ning K (1990). Seaweeds: Their Environment, Biogeography, and Ecophysiology. John Wiley and Sons, New York, 489 pp.\u003c/li\u003e\n\u003cli\u003eMabin C, Johnson C, Wright J (2019). Physiological response to temperature, light, and nitrates in the giant kelp \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e, from Tasmania, Australia. Mar Ecol Prog Ser 614: 1-19. https://doi.org/10.3354/meps12900\u003c/li\u003e\n\u003cli\u003eMacaya EC, Zuccarello GC (2010). DNA barcoding and genetic divergence in the giant kelp \u003cem\u003eMacrocystis\u003c/em\u003e (Laminariales). J Phycol 46: 736-742. https://doi.org/10.1111/j.1529-8817.2010.00845.x\u003c/li\u003e\n\u003cli\u003eMadronich S, Flocke S (1999). The role of solar radiation in atmospheric chemistry. In: Boule P (Eds) Environmental Photochemistry. The Handbook of Environmental Chemistry (2/2L) Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3- 540-69044-3_1\u003c/li\u003e\n\u003cli\u003eMarambio J, Rodr\u0026iacute;guez JP, M\u0026eacute;ndez F, Ocaranza P, Rosenfeld S, Ojeda J, Rautenberger R, Bischof K, Terrados J, Mansilla A (2017). Photosynthetic performance and pigment composition of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e (Laminariales, Phaeophyceae) along a gradient of depth and seasonality in the ecoregion of Magellan, Chile. J Appl Phycol 29: 2575-2585. https://doi.org/10.1007/s10811-017-1136-0\u003c/li\u003e\n\u003cli\u003eMayr CC, F\u0026ouml;rsterra G, H\u0026auml;ussermann V, Wunderlich A, Grau J, Zieringer M, Altenbach AV (2011). Stable isotope variability in a Chilean fjord food web: implications for N- and C-cycles. Mar Ecol Prog Ser 428: 89-104. https://doi.org/10.3354/meps09015\u003c/li\u003e\n\u003cli\u003eMinnett PJ, Brown OB, Evans RH, Key EL, Kearns EJ, Kilpatrick K, et al. (2004). Sea-surface temperature measurements from the Moderate-Resolution Imaging Spectroradiometer (MODIS) on Aqua and Terra, IGARSS 2004. 2004 IEEE International Geoscience and Remote Sensing Symposium, Anchorage, AK, USA, 7: 4576-4579. https://doi.org/10.1109/IGARSS.2004.1370173\u003c/li\u003e\n\u003cli\u003eMora-Soto A, Capsey A, Friedlander AM, Palacios M, Brewin PE, Golding N, et al. (2021). One of the least disturbed marine coastal ecosystems on Earth: spatial and temporal persistence of Darwin\u0026rsquo;s sub-Antarctic giant kelp forests. J Biogeogr 48: 2562.2577. https://doi.org/10.1111/jbi.14221\u003c/li\u003e\n\u003cli\u003eMora-Soto A, Palacios M, Macaya EC, G\u0026oacute;mez I, Huovinen P, P\u0026eacute;rez-Matus A, Young M, Golding N, Toro M, Yaqub M, Macias-Fauria M (2020). A high-resolution global map of Giant kelp (\u003cem\u003eMacrocystis pyrifera\u003c/em\u003e) forests and intertidal green algae (Ulvophyceae) with Sentinel-2 imagery. Remote Sens 12: 694. https://doi.org/10.3390/rs12040694\u003c/li\u003e\n\u003cli\u003ePalacios M, Osman D, Ram\u0026iacute;rez J, Huovinen P, G\u0026oacute;mez I (2021). Photobiology of the giant kelp \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e in the land-terminating glacier fjord Yendegaia (Tierra del Fuego): a look into the future? Sci Total Environ 751: 141810. https://doi.org/10.1016/j.scitotenv.2020.141810\u003c/li\u003e\n\u003cli\u003eR Core Team (2024). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/\u003c/li\u003e\n\u003cli\u003eReed DC, Foster MS (1984). The effects of canopy shading on algal recruitment and growth in a giant kelp forest. Ecology 65: 937-948.\u003c/li\u003e\n\u003cli\u003eRossbach S, Rossbach FI, H\u0026auml;ussermann V, F\u0026ouml;rsterra G, Laudien J (2021). In situ skeletal growth rates of the solitary cold-water coral \u003cem\u003eTethocyathus endesa\u003c/em\u003e from the Chilean Fjord region. Front Mar Sci 8: 757702. https://doi.org/10.3389/fmars.2021.757702\u003c/li\u003e\n\u003cli\u003eSantelices B, Ojeda FP (1984)a. Effect of canopy removal on the understory algal community structure of coastal forest of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e from southern South America. Mar Ecol Prog Ser 14: 165-173.\u003c/li\u003e\n\u003cli\u003eSantelices B, Ojeda FP (1984)b. Population dynamics of coastal forests of \u003cem\u003eMacrocystis pyrifera\u003c/em\u003e in Puerto Toro, lsla Navarino, Southern Chile. Mar Ecol Prog Ser 14: 176-183.\u003c/li\u003e\n\u003cli\u003eSobarzo-Bustamante M (2009). The Southern Chilean fjord region: oceanographic aspects. In: H\u0026auml;ussermann V, F\u0026ouml;rsterra G (Eds.) Marine Benthic Fauna of Chilean Patagonia (Santiago: Nature In focus) 53-60.\u003c/li\u003e\n\u003cli\u003eStephens TA, Desmond MJ, Hepburn CD (2019). Biomass across space and tide: architecture of a kelp bed with implications for the abiotic environment. Hydrobiologia 82: 391-404. https://doi.org/10.1007/s10750-018-3788-4\u003c/li\u003e\n\u003cli\u003eUmanzor S, Sandoval-Gil J, S\u0026aacute;nchez-Barredo M, Ladah LB, Ram\u0026iacute;rez-Garc\u0026iacute;a MM, Zertuche-Gonz\u0026aacute;lez JA (2021). Short-term stress responses and recovery of giant kelp (\u003cem\u003eMacrocystis pyrifera\u003c/em\u003e, Laminariales, Phaeophyceae) juvenile sporophytes to a simulated marine heatwave and nitrate scarcity. J Phycol 57: 1604-1618. https://doi.org/10.1111/jpy.13189\u003c/li\u003e\n\u003cli\u003eVillalobos VI, Valdivia N, F\u0026ouml;rsterra G, Ballyram S, Espinoza JP, Wadham JL, Burgos-Andrade K, H\u0026auml;ussermann V (2021). Depth-Dependent Diversity Patterns of Rocky Subtidal Macrobenthic Communities Along a Temperate Fjord in Northern Chilean Patagonia. Front Mar Sci 8: 635855. https://doi.org/10.3389/fmars.2021.635855\u003c/li\u003e\n\u003cli\u003eZiemann dos Santos MA, Coelho de Freitas S, Moraes-Berneira L, Mansilla A, Astorga-Espa\u0026ntilde;a, MS, Colepicolo P, Martin Pereira de Pereira C (2019). Pigment concentration, photosynthetic performance, and fatty acid profile of sub-Antarctic brown macroalgae in different phases of development from the Magellan region, Chile. J Appl Phycol 31: 2629-2642. https://doi.org/10.1007/s10811-019-01777-x\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Giant kelp forest, Comau Fjord, Photobiological characteristics, Blade morphometry, Photo-acclimation","lastPublishedDoi":"10.21203/rs.3.rs-6456951/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6456951/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eGiant kelp (\u003cem\u003eMacrocystis pyrifera\u003c/em\u003e) covers large coastal areas along the Comau Fjord (Northern Patagonia), following different environmental gradients that determine its structural complexity. In the present study, we compared the morphological (thallus length and biomass, holdfast diameter, blade morphology, etc.) and photobiological characteristics based on fluorescence (Effective Quantum Yield and P-I Curve Parameters) of six populations along the coast of Comau Fjord in three areas: Lilihuapi Island, Cahuelmo sector and Comau Fjord interior. The main results show that along the Comau Fjord, we found different structural conformations of \u003cem\u003eM. pyrifera\u003c/em\u003e populations, where only at the mouth of the fjord was it possible to record a well-established \u0026ldquo;kelp forest\u0026rdquo;, while in its interior the \u0026ldquo;cords\u0026rdquo; parallel to the coastline predominated. The major differences between these types of populations of \u003cem\u003eM. pyrifera\u003c/em\u003e populations were related to the shape of the blades (\u003cem\u003ee.g.\u003c/em\u003e, \u0026gt; blade areas in 4-CF, 5-Cf, and 6-Cf), being this a photo-acclimation strategy that responds to a marked environmental gradient along the fjord, in addition to particular geomorphology, surrounded by mountain ranges, which limits the availability of light during the pre-winter period, which translates into a balance along the Comau Fjord in its photosynthetic efficiency (α\u0026thinsp;=\u0026thinsp;0.41, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05 between sites) of optimizing light absorption. These adaptations help the algae to resist local and seasonal changes in water column conditions, adjusting its light use to low levels, similar to Antarctic brown algae, and cope with low light conditions. This type of study corresponds to the first morphological and physiological characterization of natural populations of \u003cem\u003eM. pyrifera\u003c/em\u003e in this area of Northern Patagonia and underlines the importance of continuing to collect information on a broader spatio-temporal scale to understand how stressors influence the morphology and physiology of these populations in a region that is suffering the consequences of global climate change, such as Northern Patagonia, and that is also intensely impacted by local anthropogenic activities.\u003c/p\u003e","manuscriptTitle":"First photosynthetic characterization of the giant kelp Macrocystis pyrifera from the Comau Fjord, Northern Patagonia region","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-17 13:39:26","doi":"10.21203/rs.3.rs-6456951/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-05T08:35:02+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-05T08:25:56+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"41963869436939614006318999093060322344","date":"2025-05-17T05:26:37+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-05-06T10:39:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"76561258832960944352039003087482294764","date":"2025-04-23T12:10:02+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-04-23T11:50:49+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-04-23T11:30:13+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-04-23T09:21:35+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Applied Phycology","date":"2025-04-15T17:02:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"","identity":"journal-of-applied-phycology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"10811","submissionUrl":"https://submission.nature.com/new-submission/10811/3","title":"Journal of Applied Phycology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b91ed21f-0f2e-4577-8a29-ef1a6dda4323","owner":[],"postedDate":"April 17th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-08-01T01:23:13+00:00","versionOfRecord":[],"versionCreatedAt":"2025-04-17 13:39:26","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6456951","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6456951","identity":"rs-6456951","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}