Turf algae drives coral bioerosion under high CO2

Turf algae drives coral bioerosion under high CO2 | 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 Brief Communication Turf algae drives coral bioerosion under high CO2 Joshua Heitzman, Layla Iijima, Guinther Mitushasi, Davide Spatafora, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-3779657/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Turf algal prevalence will increase in coral ecosystems under ocean acidification yet their contribution towards the ongoing and projected degradation of reefs is often overlooked. Turf algal settlement was induced on exposed coral skeleton adjacent to live coral tissue to investigate coral-turf algal interactions through a combination of laboratory and field transplantation (shallow volcanic CO 2 seep) experiments across two temperature regimes. Here, we show that turf algae are competitively favored over corals under high p CO 2 conditions. Turf algae-associated biological activity locally acidified the microenvironment overlying the exposed coral skeleton, leading to its bioerosion. Increases in coral-turf algal interactions could shift coral ecosystems towards net dissolution and should be integrated into global accretion models when considering future carbonate budgets under climate change. Earth and environmental sciences/Ocean sciences/Marine biology Earth and environmental sciences/Ecology/Climate-change ecology Figures Figure 1 Figure 2 Introduction Under current CO 2 emission scenarios, a decline of pH from 8.1 to 7.8 is expected within the coming century (SSP5-8.5 scenario 1 ), leading to a decrease in the saturation state of calcium carbonate (CaCO 3 ) in seawater (Ω aragonite ). This shift in the ocean carbonate system, referred to as ocean acidification (OA), has been shown to decrease the calcification rates of marine calcifiers 2 and increase coral skeleton porosity and fragility 3 . While OA will adversely affect coral physiology, it can also promote the growth of some algae 4 , leading to altered biological interactions that have yet unknown consequences. Turf algae, a blanket term for primitive assemblages of several algal species 5 are one of the main benthic competitor in coral reefs 6,7 , often settling onto exposed coral skeleton following disturbance events (e.g. bleaching) 8,9 . Under climate change and OA, increasing interactions between corals and turf algae could further promote the degradation of coral reefs 7 through elevated turf growth and prevalence 4,10 . Decades of investigations have provided a better understanding of the physiological effects of OA, but the ecological and biogeochemical effects remain unclear 11 . Together with the decrease in calcifying organisms, OA is driving an increase in the chemical dissolution of inert coral skeletons and coral reefs sediments 12 , which will impact coral reef carbonate budgets 13 . It has been suggested the biological activity of turf associated microbes could result in increased CO 2 release 14 , potentially leading to localized acidification in coral reefs. Despite turf algae’s global ubiquity 6,7 and common interaction with hermatypic corals 14–16 , the outcome of this competition has yet to be described under future elevated p CO 2 conditions. In this study, coral-turf algae competitive outcomes and turf algae’s contribution to CaCO 3 dissolution were investigated by creating a microcosm of coral-algae interactions, where coral microcolonies had half of their tissue stripped, providing bare coral skeleton for turf algal settlement akin to naturally occurring turf algal settlement following lesioning 15 . While aquaria experiments allow for the investigation of the isolated effects of specific stressors, OA analogues (i.e. CO 2 seeps) can be used to investigate the ecosystem-level effects of OA under ecologically realistic conditions 17 , considering the potential novel interactions that can arise in changing environments. Thus, aquaria and field transplantation (at a shallow volcanic CO 2 seep) experiments were conducted across two temperature regimes using two species of corals for each experiment from two main reef building genera: Acropora solitaryensis and Porites heronensis (warm-temperate, aquaria & field), Acropora hyacinthus and Porites cylindrica (subtropical, aquaria) (Supplementary Table 1 and Supplementary Fig. 1). We hypothesize that ( 1 ) OA may shift the competitive outcome in favor of turf algae, promoting their growth and persistence on coral skeleton and, ( 2 ) localized acidification as a result of biological activity occurring underneath the turf algal mat could compound with OA, driving CaCO 3 dissolution and bioerosion. Results and Discussion At the end of experiments, turf algal coverage on Acropora -turf algae communities increased under high p CO 2 (OA) compared to present-day conditions ( x 2 1,42 = 8.44, p = 0.004), while similar levels of high turf algal overgrowth was observed on Porites -turf algae communities under both p CO 2 conditions (mean ± se; present-day, 20.4 ± 6%; high p CO 2 (OA), 26.8 ± 7.2%; x 2 1,44 = 2.76, p = 0.097; Fig. 1 a, Supplementary Table 2 and Supplementary Figs. 2–4). Turf increase was accompanied by an equal decrease in coral tissue coverage; Acropora -turf communities were unable to recover coral tissue under OA while Porites -turf communities’ tissue recovery, or lack thereof, was similar across both p CO 2 conditions (Supplementary Figs. 3 and 4). Accretion rates followed the same trend, with Acropora -turf communities’ rates decreasing from (mean ± se) 0.031 ± 0.01 to 0.019 ± 0.003 g d − 1 ( x 2 1,41 = 10.34, p = 0.001) whereas Porites -turf communities’ rates were generally lower (0.007 ± 0.003 g d − 1 ) and unaffected by p CO 2 conditions (Fig. 1 b, Supplementary Table 2 and Supplementary Figs. 3 and 4). Furthermore, both genera of coral-turf algae communities showed a significant reduction in daily net community calcification under OA compared to present-day conditions ( Acropora : x 2 1,40 = 9.42, p = 0.002; Porites : x 2 1,43 = 13.64, p = 0.0002; Supplementary Table 2). Net daily dissolution was observed for all Acropora and Porites coral-turf communities under OA, with maximum rates of dissolution as high as 25.7 and 21.5 µmol CaCO 3 cm − 2 d − 1 , respectively (Fig. 1 c and Supplementary Figs. 3 and 4). The genera Acropora and Porites include important reef building species, and their resilience to climate change could impact the structure and function of coral reefs over the coming century. Acropora populations can recover rapidly following disturbances due to their high growth and recruitment rates 18 . On the other hand, Porites species are considered resistant to abiotic stressors including OA 19,20 , and this physiological tolerance suggests that Porites populations could remain stable under future climates 18,21 . However, both communities’ slowed tissue recovery and increased dissolution under OA highlight the importance of considering the potential ecological interactions arising under future climate conditions. Turf-algal associated biological activity was assessed through microenvironment O 2 profiles, which showed that O 2 concentrations beneath the turf algal mat had high diel oxic fluctuations. For instance, this ranged from hyperoxic in the light (mean ± sd; 757.85 ± 484.04 µmol L − 1 ) to hypoxic in the dark (34.43 ± 36.81 µmol L − 1 ; Supplementary Table 3 and Supplementary Fig. 5) under high p CO 2 conditions. Turf-associated respiration was assessed by measuring the apparent O 2 consumption rates within the turf algal mat (0–50 µm above exposed coral skeleton) in the dark. These rates did not differ across either genera of coral-turf algae communities ( Acropora : x 2 1,12 = 0.92, p = 0.337; Porites : x 2 1,12 = 0.64, p = 0.423; Supplementary Table 4), suggesting biological activity remained constant. Increased O 2 concentration under light corresponded with pH levels higher than bulk seawater pH regardless of p CO 2 conditions at both the coral tissue and turf-covered exposed coral skeleton surface (Fig. 2 a, b and Supplementary Fig. 5). In the dark, the observed pH on both the coral tissue surface ( Acropora : x 2 1,24 = 6.6, p = 0.01, Porites : x 2 1,16 = 6.72, p = 0.01) and on the turf-covered coral skeleton (Combined: x 2 1,40 = 9.54, p = 0.002; Fig. 2 a, b and Supplementary Table 2) was significantly reduced under high p CO 2 conditions compared to present-day conditions. This led to a decrease in Ω aragonite on the surface of the coral tissue surface from 3.04 ± 0.94 to 0.93 ± 0.4 (mean ± sd) and on the surface of the exposed coral skeleton beneath the turf algal mat from 4.13 ± 1.79 to 0.75 ± 0.28 (Supplementary Table 3). We interpreted these diel changes in O 2 and pH as high daytime photosynthetic production of dissolved organic carbon exudates 22 and subsequent consumption by copiotrophs 14 . As O 2 consumption rates remaining constant across p CO 2 conditions, we can infer that the turf-associated biological activity does not directly benefit from OA; rather, that dissolution is thermodynamically favored (i.e. Ω aragonite < 1) only when the biological activity of the turf algal mat is combined with elevated p CO 2 . The negative effects of OA on coral skeletal growth are typically greater under dark conditions 23,24 , suggesting live coral calcification within the coral-turf algae communities would have been decreased in our experiments. Despite the coral tissue surface exhibiting undersaturation values of Ω aragonite , the skeleton microstructure beneath it showed typical morphological features with no signs of degradation or dissolution under high p CO 2 conditions (Fig. 2 c-f and Supplementary Figs. 6–8). This suggests a form of compensatory mechanism to upregulate the pH at the calcification site 25 . Turf-covered skeletons were visibly degraded in both p CO 2 conditions (Fig. 2 g-j and Supplementary Figs. 6–8) suggesting turf algae as the main driver for the reduction of net community calcification and accretion rates. In addition, the turf-covered skeletal portion of Porites coral-turf communities showed potential signs of diagenesis in the form of aragonite needles 26 under high p CO 2 conditions (Fig. 2 j). The combined effects of turf algal driven local acidification and OA shift the community’s CaCO 3 productivity towards dissolution, thereby contributing to the ongoing bioerosion of reefs. Our findings emphasize that coral-turf algae interactions under future elevated p CO 2 conditions will accelerate the degradation of coral ecosystems and alter their function. The role of turf algae in driving bioerosion is seldom investigated under present and future climate conditions 13 . As turf algal growth and prevalence is expected to increase under OA 4,10,27 , its role as a bioeroder should be integrated into current end-of-the-century global accretion models 13 . Methods Aquaria experiment setup Aquaria experiment tanks were continuously supplied with fresh unfiltered seawater pumped from a depth of 2 and 5 m from a nearby bay in front of the Tropical Biosphere Research Center (Sesoko island, Okinawa, Japan; 26° 38' 13" N 127° 51' 53" E) and the Shimoda Marine Research Center (Shimoda city, Japan; 34° 39' 57" N 138° 56' 20" E; Supplementary Fig. 1 and Table 1). Each experimental tank (length × width × height; Sesoko: 3.5 L, 20 × 15 × 15 cm; Shimoda: 16 L, 30 × 20 × 30 cm) was continuously aerated, with aquarium lights (ZetLight © Lancia2 Series, USA) maintained at 5.01 ± 1.43 mol photons m 2 s -1 for 12 hours each day. Each tank was outfitted with a pH and temperature sensor (Neptune Systems, USA), logging real-time measurements every five minutes. In order to control pH within experimental tanks, CO 2 was bubbled using a fine air stone (LSS Laboratory, Japan) controlled by both a solenoid and needle valve (LSS Laboratory, Japan). The solenoid valve, which controls opening and closing periods, was maintained using an APEX aquarium system (Neptune Systems, USA), which was also used for measurement and logging of the real-time pH and temperature of all tanks. Two p CO 2 conditions were chosen for all aquaria experiments: a present-day p CO 2 condition with ambient unfiltered natural seawater, and a high p CO 2 condition maintained at 7.85 pH in accordance with the SSP5-8.5 scenario 1 . Each tank’s respective pH value was corrected based on a pH reading measured using a multi-sensor (ThermoScientific™ Orion Star™ A326, USA). Using pH values from the in-tank pH sensor and stand-alone multi-sensor, we calculated the difference and corrected the pH value in which the CO 2 solenoid valve would open and close, allowing us to set up the APEX pH system accurately. All experimental aquaria tanks had a small aquarium corner pump to induce water movement (GEX, Japan). Coral preparation The Shimoda aquaria ( n = 10) and Shikine island transplantation ( n = 6) experiments both used Acropora solitaryensis 2 and Porites heronensis 3 , which were sampled at Shikine island (Tokyo Prefecture, Japan, 34° 19' 34" N 139° 12' 36" E) and at Shimoda city (Shizuoka Prefecture, Japan, 34° 39' 58.1" N 138° 56' 33.6" E), respectively (Supplementary Fig. 1 and Supplementary Table 1). The Sesoko aquaria experiment ( n = 5) used Acropora hyacinthus 4 and Porites cylindrica 4 sampled at the bay in front of the Sesoko Research station (26° 38' 13" N 127° 51' 53" E; Supplementary Fig. 1 and Supplementary Table 1). To avoid potential genotype bias, coral colonies were sampled equivalent to their replicate number. Following sampling, each colony was split into two ~30 cm 2 sized microcolonies for each p CO 2 condition (present-day, high p CO 2 (OA)). All microcolonies had half of their tissue stripped using pressurized air, leaving behind bare coral skeleton. These half-and-half tissue and bare skeleton microcolonies were then acclimated for around a week in each of their respective environments (aquaria, field), where naturally present turf algae settled onto the bare skeleton portion. The Shimoda and Sesoko aquaria experiment durations were 111 (2021-10-12 to 2022-01-31) and 31 (2023-07-28 to 2023-08-28) days, respectively. Field transplantation experiment setup The field transplantation experiment was conducted at Shikine island (Tokyo Prefecture, Japan, 34° 19' 34" N 139° 12' 36" E), which is regarded as an analogue for ocean acidification (OA) due to its CO 2 seeps 5 . The experiment was conducted from 2022-08-12 to 2023-04-05 (236 days). Specimens were transplanted to two sites with differing p CO 2 conditions: a present-day site (Mikawa bay, mean ± se, pH 8.26 ± 0.001, pCO 2 317.325 µatm) and a high p CO 2 (OA) site (pH 7.832 ± 0.003, pCO 2 1005.173 µatm; Supplementary Fig. 1 and Supplementary Table 1) To fix specimens to each site, all microcolonies were epoxied (E380 underwater bonder, Konishi Company, Japan) onto ~8 × 8 cm PVC tiles, which were subsequently attached to 30 cm long steel bars. Bars were set up using anchor bolts (8.5 mm width, 70 mm length) drilled into rock by SCUBA divers at ~8 m depth (Nemo Underwater Drill). Bars at both locations were deployed haphazardly within a circa 100 m 2 area, with a distance of ~5 m between each bar. Following retrieval of experimental specimens, they were incubated according to their respective p CO 2 conditions in the aforementioned aquaria tank system for physiological measurements and microsensor profiling. Environmental parameters at both sites were assessed during the experiment duration, with pH measurements taken in situ using a pH logger (HOBO, USA), and seawater sampled for total alkalinity ( n = 3) at both sites. Total alkalinity was measured using an automatic titrator (916 Ti-Touch, Metrohm AG, Switzerland), with details outlined in the following methods for measurements of net community calcification. Measurements Competition outcome Competition outcome was assessed by photographing each microcolony from a top-down angle at the beginning and end of each experiment and measuring the surface area of the live coral tissue and the portion of exposed coral skeleton covered with turf algae, using ImageJ 6 . Surface area was then converted as a percentage of total colony area and shown as a rate of change throughout the experimental duration (days). Accretion rate Accretion rates were calculated using the buoyant weight technique 7 by measuring the weight of all microcolonies at the start and end of each experiment and shown as a rate of change throughout the experimental duration (days). Net community calcification Net community calcification was measured using the alkalinity anomaly method 8 . We measured total alkalinity at the start and end of a 12 (Shimoda aquaria, Shikine transplantation) and 3 (Sesoko aquaria)-hour incubation period under both light and dark conditions at the end of all experiments. Prior to measurement, each microcolony was isolated into individual tanks. Following isolation, start samples (~50 mL seawater) were taken, seawater input was halted, with CO 2 and air still bubbling to maintain pH and oxygen levels over the extended incubation periods. Titration of total alkalinity samples was done using an automatic titrator (916 Ti-Touch, Metrohm AG, Switzerland), using 0.1 mol L -1 HCl (Wako, Japan) as measurement solution. The pH electrode was calibrated on the total scale with Tris buffer in artificial seawater solution (Wako, Japan). Total alkalinity calculation was done using an R script adapted from the R package ‘seacarb’ 9 . Alkalinity measurements were validated using a running standard consisting of aged seawater for which the total alkalinity was checked against CRM materials obtained from Dickson’s lab (batch number: 152) Net community calcification is shown as a rate of calcium carbonate (CaCO 3 ) changedaily (12 hours light, 12 hours dark). Surface area Surface area measurements of all measured microcolony fragments were done using both the wax 10 and foil methods 11 . All microcolony fragments were first cleaned in a 0.1 mmol bleach solution, and subsequently dried at room temperature (~25 °C). Following this step, initial weight was measured (HR-60, A & D, Japan). Paraffin wax was melted at 60 °C in a container within a water bath (Smart Water Bath, AS ONE, Japan), and all samples were dipped and then shaken for three seconds each. Post and pre-wax weights were then standardized using the foil weights of a subset of colonies for each species. SEM micrography Following the cleaning step used for surface area measurements, all samples were dried at 60°C in an oven and then desiccated in a vacuum chamber containing P 4 O 10 until completely dry. All samples were then placed into a tabletop SEM for imaging (JCM-5000 NeoScope™ Tabletop SEM, Japan). Past literature was used to identify forms of diagenesis observed within our samples 12,13 . Microsensor measurements Microsensor tank setup Microsensor measurements were done within four days following the end of the Shimoda aquaria and Shikine island transplantation experiments. A 60 × 25 × 15 cm (length × width × height) acrylic flow-through tanks outfitted with flow straighteners on both sides of the measurement area were used for incubating microcolonies when taking microsensor measurements (Supplementary Fig. 9). We used a closed-system setup, filled with filtered natural seawater (0.2 µm cartridge filter, Advantec, Japan), with flowrate maintained at ~3 cm s -1 , with water continuously aerated using an aquarium pump (Japan Pet Design, JET, Japan). An aquarium light (Radion G3, Ecotech Marine, USA) maintained at ~5 mol m 2 d -1 was used when conducting measurements for light settings. Dark settings were maintained by covering the entire system with a blackout sheet. For microsensor observation, we used a stereoscope (LabScope ZEISS, Sony, Japan) attached to a boom stand (SZ-STU1, Olympus, Japan), and was outfitted with a small lamp used when placing and lowering microsensors in dark settings. Microsensor setup and calibration Coral and turf algae covered exposed coral skeleton oxygen concentrations (O 2 ) were measured using a Clark-type O 2 glass microsensor (tip size of 40–60 μm; Ox-50 Unisense A/S, Aarhus, Denmark). Calibration was done as follows: an O 2 zero reading was accomplished by preparing a sodium sulfite and filtered seawater solution at 0.1 M concentration (Na 2 SO 3 , Nacalai Tesque, Japan) following the manufacturer’s instructions, an O 2 saturation state was accomplished by bubbling air into the filtered seawater using a simple air pump for at least 15 minutes. Coral and turf algae covered exposed coral skeletal surface pH was measured using pH glass microelectrodes (tip size of 40 - 60 μm; pH-50 Unisense A/S, Aarhus, Denmark). The microelectrode was connected to a reference electrode (Unisense A/S, Aarhus, Denmark). Calibration was done using standard NBS calibration buffer solution (pH 4, 7, 10; NIST Traceable Solutions, USA). Both microsensors were connected to the UniAmp Multi Channel (UniAmp Multi Channel; Unisense A/S, Aarhus, Denmark), which directly connected to a computer using the SensorTrace software, used for all microsensor measurements and profiling (SensorTrace Suite; Unisense A/S, Aarhus, Denmark). A dual-head manual micromanipulator (MM33-2; Unisense A/S, Aarhus, Denmark) was used to hold and control both microsensors simultaneously. The seawater within the microsensor measurement tank was also logged using a multi-sensor (ThermoScientific™ Orion Star™ A326, USA) outfitted with a dissolved oxygen (DO) and pH/temperature sensor, as to ensure the accuracy and as an above-CBL (concentration boundary layer) comparison of the microsensor O 2 and pH readings. Microsensor profiles Coral-turf algal communities from each p CO 2 condition and species were chosen at random for pH ( Acropora Coral tissue: n = 12 per light and p CO 2 condition, Porites Coral Tissue: present-day: n = 10 per light condition, high p CO 2 (OA): n = 6 (Light) & n = 7 (Dark), Turf algae: n = 24 per light and p CO 2 condition) and O 2 ( Acropora & Porites Coral tissue: n = 6 per light and p CO 2 condition, Turf algae: n = 12 per light and p CO 2 condition) microsensor profiling (Supplementary Table 2). Measurements from the Shimoda aquaria and Shikine island transplantation experiments were pooled for pH data, whereas O 2 data is only from the Shimoda experiment. Microsensor depth profiles were taken in both light and dark settings at four points (two measurements per location) on each microcolony: (1) coral tissue and (2) turf algae covered exposed coral skeleton (Supplementary Fig. 10). All colonies were acclimated for at least one hour to their respective light and p CO 2 conditions prior to measurements. Before measuring depth profiles for each measurement, pH and O 2 readings above the concentration boundary layer (CBL) were noted. Depth profiles began at the surface for each measurement location (Coral tissue: on the coral tissue, Turf algae: on the exposed coral skeleton underneath the turf algae), with one measurement taken every 10 μm until pH and O 2 had returned to tank (above-CBL) values. Following each measurement profile, both sensors were washed using filtered seawater to strip off potentially attached turf algae and mucus. Tank seawater was changed after conducting all measurements of one coral colony. All profiled coral-turf algae community colonies were orientated the same, with turf algae on the downstream of living coral tissue, to avoid CBL-induced differences on the coral tissue via turf algae influence (Supplementary Fig. 10). Data analyses All figures were generated with R software v4.2.2 14 . We used ‘ggplot2’, ‘forcats’, ‘dplyr’, ‘tibble’ and ‘scales’ packages from the ‘tidyverse’ 15 , ‘ggpubr’ 16 , ‘rstatix’ 17 , ‘ggsignif’ 18 and ‘patchwork’ 19 packages for all figure production and data analysis. Figures containing photo panels were created using the Inkscape graphics editing software 20 . Competition outcome, accretion rates, net community calcification rates, and pH microsensor profile data were assessed using a linear mixed model (lmm) using the function ‘lmer’ from the package ‘lme4’ 21 for the model, and ‘Anova’ for the subsequent test from the package ‘car’ 22 . For each model, data from all experiments was pooled, and our fixed factor was p CO 2 condition (fixed factor with two levels: present-day, high p CO 2 (OA)) for each coral-turf algae genera ( Acropora , Porites ), with Experiment as the random factor (Shimoda, Shikine, Sesoko). Comparisons between mean values (dashed lines) of both p CO 2 conditions across each Experiment (Red: Shimoda, Green: Shikine, Blue: Sesoko) was plotted together with the predicted mean values (solid lines) from our linear mixed model for both Acropora and Porites coral-algae communities for competition outcome, accretion rates and net community calcification rates (Supplementary Figure 4). For pH microsensor profiles, the lowest measurement (Depth = 0 µm), being the surface of the coral tissue and exposed skeleton underneath the turf algae values (Coral tissue, Turf algae) were tested for both for the coral tissue of Acropora and Porites and turf algae from both genera undertwo light conditions (Light, Dark). For models that showed significance, we validated our models by first comparing the AIC (Akaike information criteria) scores following an analysis of variance (‘anova’ function) between models with and without the fixed factor of p CO 2 condition (Supplementary Table 2). Following this, we used the function ‘performance’ from the package ‘performance’ 23 to produce a set of indices describing the model fit (Supplementary Table 2). The scores (AIC, AICc, BIC (Bayesian information criterion), R2 conditional, R2 marginal, ICC (Intraclass correlation), RMSE (Root-mean square deviation), Sigma) suggest the pooling and subsequent usage of Experiment as a random factor are adequate based on similar methods described in previous studies 24,25 . The diffusive oxygen fluxes between 0 and 50 µm above the exposed coral skeleton beneath the turf algal mat were calculated using Fick’s first law assuming a flat surface without substantial heterogeneity and following Kühl et al 26 : with the O 2 diffusion constant D = 2.35 mol cm 2 s -1 (25 °C and 35 ‰ salinity seawater), Δ[O 2 ] the difference between the O 2 concentrations at the surface of the turf-covered exposed skeleton surface (0 µm) and the one at 50 µm above, Δx = 0.0050 cm. The diffusion constant was not corrected for porosity and tortuosity 27 with the assumption that it would be similar in both treatments. Oxygen flux values were compared using Kruskal-Wallis tests, with p CO 2 condition as fixed factor (with two levels: present-day, high p CO 2 (OA)) and compared for each coral-turf algae genera ( Acropora , Porites ) and light condition (Light, Dark) (Supplementary Table 4). The seawater saturation state of aragonite (Ω Aragonite) of the surface of the coral tissue and sub-turf algal layer’s microchemical environment was calculated from pH microsensor profiles together with the seawater temperature and the total alkalinity of the microsensor holding tank using the excel calculator program ‘CO2SYS’ 28 . References for methods 1. Calvin, K. et al. IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. 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Open Source Softw. 6 , 3139 (2021). 24. Poore, A. G. B. et al. Global patterns in the impact of marine herbivores on benthic primary producers. Ecol. Lett. 15 , 912–922 (2012). 25. Ruiz-Moreno, D. et al. Global coral disease prevalence associated with sea temperature anomalies and local factors. Dis. Aquat. Organ. 100 , 249–61 (2012). 26. Kühl, M. et al. Microenvironment and photosynthesis of zooxanthellae in scleractinian corals studied with microsensors for O sub(2), pH and light. Mar. Ecol. Prog. Ser. 117 , 159–172 (1995). 27. Gieseke, A. & De Beer, D. Section 8 update: Use of microelectrodes to measure in situ microbial activities in biofilms, sediments, and microbial mats. in Molecular Microbial Ecology Manual (eds. Kowalchuk, G. A., De Bruijn, F. J., Head, I. M., Akkermans, A. D. & Van Elsas, J. D.) 3483–3514 (Springer Netherlands, 2008). doi:10.1007/978-1-4020-2177-0_802. 28. Pierrot, D., Lewis, E. & Wallace, D. MS Excel Program Developed for CO2 System Calculations ORNL/CDIAC-105, Carbon Dioxide Inf. Anal Cent Oak Ridge Natl Lab U Dept Energy Oak Ridge Tenn Httpscdiac Ess-Dive Lbl Govftpco2sysCO2SYScalcXLSv2 1 , (2006). Declarations Acknowledgements This project contributes towards the International CO 2 Natural Analogues (ICONA) Network. The authors would like to acknowledge the technical staff (Manabu Ooue, Jiro Takano, Daisuke Shibata, Toshihiko Sato, Chika Nakamura) of the Shimoda Marine Research Center (University of Tsukuba) for assistance in sampling and transplantation of corals in the field. The authors also thank the students and faculty at the Shimoda Marine Research Center and the Sesoko Station for their role in discussing the results of this study. Thank you to Dr. Shunsuke Yaguchi for assistance with preparation and analysis of samples using the SEM. Special thanks to Kayo Takonai (lab technician) who assisted in processing and analyzing total alkalinity samples. Funding This work was partially funded by the JST SPRING grant (Grant Number JPMJSP2124 2021) and was partially funded by the Japan Society for the Promotion of Science (JSPS) Core-to-Core Program (Grant Number: JPJSCCA20210006). CRediT authorship contribution statement Joshua M. Heitzman : Conceptualization, Methodology, Formal analysis, Resources, Investigation, Data curation, Visualization, Writing - Original draft, Writing - Review & Editing, Funding acquisition Layla Iijima : Formal analysis, Investigation, Writing - Review & Editing Guinther Mitushasi : Formal analysis, Investigation, Writing - Review & Editing Davide Spatafora : Formal analysis, Writing - Review & Editing Shigeki Wada : Writing - Review & Editing, Funding acquisition Ben P. Harvey : Writing - Review & Editing, Funding acquisition Haruko Kurihara : Investigation, Resources, Writing - Review & Editing, Supervision Sylvain Agostini : Conceptualization, Methodology, Formal analysis, Investigation, Resources, Visualization, Writing - Review & Editing, Project administration, Supervision, Funding acquisition Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Data availability R code for figure production and raw data are available on the GitHub repository: https://github.com/joheitzman/OA_Turf References Calvin, K. et al. IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland. https://www.ipcc.ch/report/ar6/syr/ (2023) doi:10.59327/IPCC/AR6-9789291691647. Hoegh-Guldberg, O. et al. Coral Reefs Under Rapid Climate Change and Ocean Acidification. Science 318 , 1737–1742 (2007). Tambutté, E. et al. Morphological plasticity of the coral skeleton under CO2-driven seawater acidification. Nat. Commun. 6 , 7368 (2015). Connell, S. D. et al. The duality of ocean acidification as a resource and a stressor. Ecology 99 , 1005–1010 (2018). Connell, S. D., Foster, M. S. & Airoldi, L. What are algal turfs? Towards a better description of turfs. Mar. Ecol. Prog. Ser. 495 , 299–307 (2014). Smith, J. E. et al. Re-evaluating the health of coral reef communities: baselines and evidence for human impacts across the central Pacific. Proc. R. Soc. B Biol. Sci. 283 , 20151985 (2016). Tebbett, S. B., Connolly, S. R. & Bellwood, D. R. Benthic composition changes on coral reefs at global scales. Nat. Ecol. Evol. 7 , 71–81 (2023). Diaz-Pulido, G. & McCook, L. The fate of bleached corals: patterns and dynamics of algal recruitment. Mar. Ecol. Prog. Ser. 232 , 115–128 (2002). Ostrander, G. K., Armstrong, K. M., Knobbe, E. T., Gerace, D. & Scully, E. P. Rapid transition in the structure of a coral reef community: The effects of coral bleaching and physical disturbance. Proc. Natl. Acad. Sci. 97 , 5297–5302 (2000). Harvey, B. P. et al. Feedback mechanisms stabilise degraded turf algal systems at a CO2 seep site. Commun. Biol. 4 , 1–10 (2021). Shi, Y. & Li, Y. Impacts of ocean acidification on physiology and ecology of marine invertebrates: a comprehensive review. Aquat. Ecol. (2023) doi:10.1007/s10452-023-10058-2. Eyre, B. D. et al. Coral reefs will transition to net dissolving before end of century. Science 359 , 908–911 (2018). Cornwall, C. E. et al. Global declines in coral reef calcium carbonate production under ocean acidification and warming. Proc. Natl. Acad. Sci. 118 , e2015265118 (2021). Haas, A. F. et al. Global microbialization of coral reefs. Nat. Microbiol. 1 , 1–7 (2016). Barott, K. L. & Rohwer, F. L. Unseen players shape benthic competition on coral reefs. Trends Microbiol. 20 , 621–628 (2012). Brown, K. T. et al. The Dynamics of Coral-Algal Interactions in Space and Time on the Southern Great Barrier Reef. Front. Mar. Sci. 5 , (2018). Hall-Spencer, J. M. et al. Volcanic carbon dioxide vents show ecosystem effects of ocean acidification. Nature 454 , 96–99 (2008). Woesik, R. van, Sakai, K., Ganase, A. & Loya, Y. Revisiting the winners and the losers a decade after coral bleaching. Mar. Ecol. Prog. Ser. 434 , 67–76 (2011). Agostini, S. et al. Greater Mitochondrial Energy Production Provides Resistance to Ocean Acidification in “Winning” Hermatypic Corals. Front. Mar. Sci. 7 , (2021). Comeau, S. et al. Resistance to ocean acidification in coral reef taxa is not gained by acclimatization. Nat. Clim. Change 9 , 477–483 (2019). Hughes, T. P. et al. Global warming transforms coral reef assemblages. Nature 556 , 492–496 (2018). Haas, A. F. et al. Influence of coral and algal exudates on microbially mediated reef metabolism. PeerJ 1 , e108 (2013). Bove, C. B., Whitehead, R. F. & Szmant, A. M. Responses of coral gastrovascular cavity pH during light and dark incubations to reduced seawater pH suggest species-specific responses to the effects of ocean acidification on calcification. Coral Reefs 39 , 1675–1691 (2020). Chou, W.-C., Liu, P.-J., Chen, Y.-H. & Huang, W.-J. Contrasting Changes in Diel Variations of Net Community Calcification Support That Carbonate Dissolution Can Be More Sensitive to Ocean Acidification Than Coral Calcification. Front. Mar. Sci. 7 , (2020). Georgiou, L. et al. pH homeostasis during coral calcification in a free ocean CO2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef. Proc. Natl. Acad. Sci. 112 , 13219–13224 (2015). Bar-Matthews, M., Wasserburg, G. J. & Chen, J. H. Diagenesis of fossil coral skeletons: Correlation between trace elements, textures, and 234U238U. Geochim. Cosmochim. Acta 57 , 257–276 (1993). Enochs, I. C. et al. Ocean acidification enhances the bioerosion of a common coral reef sponge: implications for the persistence of the Florida Reef Tract. Bull. Mar. Sci. 91 , 271–290 (2015). Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryInformation.pdf Cite Share Download PDF Status: Under Review Version 1 posted 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. 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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-3779657","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Brief Communication","associatedPublications":[],"authors":[{"id":266478138,"identity":"d946fe03-8f5e-4d15-8e88-c34eacfb321b","order_by":0,"name":"Joshua Heitzman","email":"","orcid":"https://orcid.org/0000-0002-8275-5006","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan","correspondingAuthor":false,"prefix":"","firstName":"Joshua","middleName":"","lastName":"Heitzman","suffix":""},{"id":266478139,"identity":"e9fd0326-8585-461b-9436-c2156a291ef7","order_by":1,"name":"Layla Iijima","email":"","orcid":"https://orcid.org/0000-0001-9652-0155","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan","correspondingAuthor":false,"prefix":"","firstName":"Layla","middleName":"","lastName":"Iijima","suffix":""},{"id":266478140,"identity":"0be36c6d-28eb-437b-8e27-42256db711d3","order_by":2,"name":"Guinther Mitushasi","email":"","orcid":"","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan","correspondingAuthor":false,"prefix":"","firstName":"Guinther","middleName":"","lastName":"Mitushasi","suffix":""},{"id":266478141,"identity":"4f2c3f2e-476f-429a-8c8c-092e9fb0e268","order_by":3,"name":"Davide Spatafora","email":"","orcid":"","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan; Stazione Zoologica Anton Dohrn Department of Integrative Marine Ecology, Sicily Marine Center, Lungomare Cristoforo Colombo (complesso Roosevelt), 90149, Palermo, Italy","correspondingAuthor":false,"prefix":"","firstName":"Davide","middleName":"","lastName":"Spatafora","suffix":""},{"id":266478142,"identity":"9082d344-909b-4ac0-9685-cd26beee75a0","order_by":4,"name":"Shigeki Wada","email":"","orcid":"","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan","correspondingAuthor":false,"prefix":"","firstName":"Shigeki","middleName":"","lastName":"Wada","suffix":""},{"id":266478143,"identity":"1f160797-42f3-4215-83fb-ce2e5cec7324","order_by":5,"name":"Ben P. Harvey","email":"","orcid":"","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan","correspondingAuthor":false,"prefix":"","firstName":"Ben","middleName":"P.","lastName":"Harvey","suffix":""},{"id":266478144,"identity":"72e5b742-1f25-4843-ac63-4a2ed049f1a0","order_by":6,"name":"Haruko Kurihara","email":"","orcid":"","institution":"Department of Chemistry, Biology, and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa, 903-0213, Japan","correspondingAuthor":false,"prefix":"","firstName":"Haruko","middleName":"","lastName":"Kurihara","suffix":""},{"id":266478137,"identity":"80f90367-5b8f-47ff-9c6f-1e1d5bcbb4a4","order_by":7,"name":"Sylvain Agostini","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0001-9040-9296","institution":"Shimoda Marine Research Center, University of Tsukuba, 5-10-1 Shimoda, Shizuoka, Japan","correspondingAuthor":true,"prefix":"","firstName":"Sylvain","middleName":"","lastName":"Agostini","suffix":""}],"badges":[],"createdAt":"2023-12-20 03:50:08","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-3779657/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-3779657/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":50180157,"identity":"c238abd5-f3ae-4cd7-adf2-4b92c199469d","added_by":"auto","created_at":"2024-01-25 17:52:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1019322,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a) Turf algal coverage change (%) and (b) accretion rates (g\u003c/em\u003e\u003csup\u003e\u003cem\u003e \u003c/em\u003e\u003c/sup\u003e\u003cem\u003ed\u003c/em\u003e\u003csup\u003e\u003cem\u003e-1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e) of Acropora\u003c/em\u003e \u003cem\u003eand\u003c/em\u003e \u003cem\u003ePorites\u003c/em\u003e \u003cem\u003ecoral-turf algae communities from the start to the end of aquaria experiments (Shimoda: circle, Sesoko: cross) and the field transplantation experiment (Shikine: square). (c) The daily net community calcification rate (µmol CaCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e3\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e cm\u003c/em\u003e\u003csup\u003e\u003cem\u003e-2\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e d\u003c/em\u003e\u003csup\u003e\u003cem\u003e-1\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e) for Acropora and Porites coral-turf algae communities at the end of each experiment. Plots are separated by pCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e conditions (present-day: blue, high pCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e (OA): red). (d-g) Dashed lines represent to scale the portion of coral tissue (green) and exposed coral skeleton (yellow) at the start of the transplantation experiment conducted at the Shikine island CO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2 \u003c/em\u003e\u003c/sub\u003e\u003cem\u003eseep. (d, e) Acropora and (f, g) Porites colonies from the present-day and high pCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e conditions, respectively, at the end of the transplantation experiment conducted at the Shikine island CO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2 \u003c/em\u003e\u003c/sub\u003e\u003cem\u003eseep. Scale bars represent 5 cm.\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-3779657/v1/5740b72a0a01b0c47f20e7cc.png"},{"id":50180554,"identity":"a920f14f-e0a0-4e23-8f72-79118d75ec3e","added_by":"auto","created_at":"2024-01-25 18:00:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1233190,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003epH microsensor profiles (NBS scale) of coral-turf algae communities on the surface of the (a) coral tissue and (b) exposed coral skeleton underneath turf algae in light (open circle) and dark (filled circle) settings under present-day (blue) and high pCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e (OA, red) conditions. Values are shown as mean ± se for each measurement depth (µm). The dashed line represents an estimated saturation state of aragonite (Ω\u003c/em\u003e\u003csub\u003e\u003cem\u003earagonite\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e) of one. SEM micrographs of representative Acropora and Porites coral-turf algal communities from the Shimoda aquaria experiment showing the skeleton under (c-f) the coral tissue and (g-j) turf algae under present-day and high pCO\u003c/em\u003e\u003csub\u003e\u003cem\u003e2\u003c/em\u003e\u003c/sub\u003e\u003cem\u003e conditions. Skeletal features are labelled and abbreviated as follows: Sp (Spinulae), Sep (Septa), Th (Theca), DSp (Degraded Spinulae), DSep (Degraded Septa), DTh (Degraded Theca), RS (Rugose Surface), AN (Aragonite Needles).\u003c/em\u003e\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-3779657/v1/27030865552d74f6614cc442.png"},{"id":50219483,"identity":"f0bbdf92-ec91-4445-8d99-9d14b635db22","added_by":"auto","created_at":"2024-01-26 15:31:44","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1907495,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3779657/v1/f9c36be2-18c9-4c8a-b4b6-27a9429b83fb.pdf"},{"id":50180158,"identity":"ef3f5470-6bcf-4619-8746-7a5d6b8c0af9","added_by":"auto","created_at":"2024-01-25 17:52:26","extension":"pdf","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":3214027,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-3779657/v1/bfc45fe64b17c55cffa044b8.pdf"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Turf algae drives coral bioerosion under high CO2","fulltext":[{"header":"Introduction","content":"\u003cp\u003eUnder current CO\u003csub\u003e2\u003c/sub\u003e emission scenarios, a decline of pH from 8.1 to 7.8 is expected within the coming century (SSP5-8.5 scenario \u003csup\u003e1\u003c/sup\u003e), leading to a decrease in the saturation state of calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e) in seawater (Ω\u003csub\u003earagonite\u003c/sub\u003e). This shift in the ocean carbonate system, referred to as ocean acidification (OA), has been shown to decrease the calcification rates of marine calcifiers \u003csup\u003e2\u003c/sup\u003e and increase coral skeleton porosity and fragility \u003csup\u003e3\u003c/sup\u003e. While OA will adversely affect coral physiology, it can also promote the growth of some algae \u003csup\u003e4\u003c/sup\u003e, leading to altered biological interactions that have yet unknown consequences. Turf algae, a blanket term for primitive assemblages of several algal species \u003csup\u003e5\u003c/sup\u003e are one of the main benthic competitor in coral reefs \u003csup\u003e6,7\u003c/sup\u003e, often settling onto exposed coral skeleton following disturbance events (e.g. bleaching) \u003csup\u003e8,9\u003c/sup\u003e. Under climate change and OA, increasing interactions between corals and turf algae could further promote the degradation of coral reefs \u003csup\u003e7\u003c/sup\u003e through elevated turf growth and prevalence \u003csup\u003e4,10\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eDecades of investigations have provided a better understanding of the physiological effects of OA, but the ecological and biogeochemical effects remain unclear \u003csup\u003e11\u003c/sup\u003e. Together with the decrease in calcifying organisms, OA is driving an increase in the chemical dissolution of inert coral skeletons and coral reefs sediments \u003csup\u003e12\u003c/sup\u003e, which will impact coral reef carbonate budgets \u003csup\u003e13\u003c/sup\u003e. It has been suggested the biological activity of turf associated microbes could result in increased CO\u003csub\u003e2\u003c/sub\u003e release \u003csup\u003e14\u003c/sup\u003e, potentially leading to localized acidification in coral reefs. Despite turf algae\u0026rsquo;s global ubiquity \u003csup\u003e6,7\u003c/sup\u003e and common interaction with hermatypic corals \u003csup\u003e14\u0026ndash;16\u003c/sup\u003e, the outcome of this competition has yet to be described under future elevated \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions. In this study, coral-turf algae competitive outcomes and turf algae\u0026rsquo;s contribution to CaCO\u003csub\u003e3\u003c/sub\u003e dissolution were investigated by creating a microcosm of coral-algae interactions, where coral microcolonies had half of their tissue stripped, providing bare coral skeleton for turf algal settlement akin to naturally occurring turf algal settlement following lesioning \u003csup\u003e15\u003c/sup\u003e. While aquaria experiments allow for the investigation of the isolated effects of specific stressors, OA analogues (i.e. CO\u003csub\u003e2\u003c/sub\u003e seeps) can be used to investigate the ecosystem-level effects of OA under ecologically realistic conditions \u003csup\u003e17\u003c/sup\u003e, considering the potential novel interactions that can arise in changing environments. Thus, aquaria and field transplantation (at a shallow volcanic CO\u003csub\u003e2\u003c/sub\u003e seep) experiments were conducted across two temperature regimes using two species of corals for each experiment from two main reef building genera: \u003cem\u003eAcropora solitaryensis\u003c/em\u003e and \u003cem\u003ePorites heronensis\u003c/em\u003e (warm-temperate, aquaria \u0026amp; field), \u003cem\u003eAcropora hyacinthus\u003c/em\u003e and \u003cem\u003ePorites cylindrica\u003c/em\u003e (subtropical, aquaria) (Supplementary Table\u0026nbsp;1 and Supplementary Fig.\u0026nbsp;1). We hypothesize that (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) OA may shift the competitive outcome in favor of turf algae, promoting their growth and persistence on coral skeleton and, (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) localized acidification as a result of biological activity occurring underneath the turf algal mat could compound with OA, driving CaCO\u003csub\u003e3\u003c/sub\u003e dissolution and bioerosion.\u003c/p\u003e"},{"header":"Results and Discussion","content":"\u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the end of experiments, turf algal coverage on \u003cem\u003eAcropora\u003c/em\u003e-turf algae communities increased under high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA) compared to present-day conditions (\u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,42\u003c/sub\u003e = 8.44, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.004), while similar levels of high turf algal overgrowth was observed on \u003cem\u003ePorites\u003c/em\u003e-turf algae communities under both \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;se; present-day, 20.4\u0026thinsp;\u0026plusmn;\u0026thinsp;6%; high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA), 26.8\u0026thinsp;\u0026plusmn;\u0026thinsp;7.2%; \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,44\u003c/sub\u003e = 2.76, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.097; Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, Supplementary Table\u0026nbsp;2 and Supplementary Figs.\u0026nbsp;2\u0026ndash;4). Turf increase was accompanied by an equal decrease in coral tissue coverage; \u003cem\u003eAcropora\u003c/em\u003e-turf communities were unable to recover coral tissue under OA while \u003cem\u003ePorites\u003c/em\u003e-turf communities\u0026rsquo; tissue recovery, or lack thereof, was similar across both \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions (Supplementary Figs.\u0026nbsp;3 and 4). Accretion rates followed the same trend, with \u003cem\u003eAcropora\u003c/em\u003e-turf communities\u0026rsquo; rates decreasing from (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;se) 0.031\u0026thinsp;\u0026plusmn;\u0026thinsp;0.01 to 0.019\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003 g d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (\u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,41\u003c/sub\u003e = 10.34, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.001) whereas \u003cem\u003ePorites\u003c/em\u003e-turf communities\u0026rsquo; rates were generally lower (0.007\u0026thinsp;\u0026plusmn;\u0026thinsp;0.003 g d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and unaffected by \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, Supplementary Table\u0026nbsp;2 and Supplementary Figs.\u0026nbsp;3 and 4). Furthermore, both genera of coral-turf algae communities showed a significant reduction in daily net community calcification under OA compared to present-day conditions (\u003cem\u003eAcropora\u003c/em\u003e: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,40\u003c/sub\u003e = 9.42, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002; \u003cem\u003ePorites\u003c/em\u003e: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,43\u003c/sub\u003e = 13.64, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.0002; Supplementary Table\u0026nbsp;2). Net daily dissolution was observed for all \u003cem\u003eAcropora\u003c/em\u003e and \u003cem\u003ePorites\u003c/em\u003e coral-turf communities under OA, with maximum rates of dissolution as high as 25.7 and 21.5 \u0026micro;mol CaCO\u003csub\u003e3\u003c/sub\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e d\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec and Supplementary Figs.\u0026nbsp;3 and 4).\u003c/p\u003e \u003cp\u003eThe genera \u003cem\u003eAcropora\u003c/em\u003e and \u003cem\u003ePorites\u003c/em\u003e include important reef building species, and their resilience to climate change could impact the structure and function of coral reefs over the coming century. \u003cem\u003eAcropora\u003c/em\u003e populations can recover rapidly following disturbances due to their high growth and recruitment rates \u003csup\u003e18\u003c/sup\u003e. On the other hand, \u003cem\u003ePorites\u003c/em\u003e species are considered resistant to abiotic stressors including OA \u003csup\u003e19,20\u003c/sup\u003e, and this physiological tolerance suggests that \u003cem\u003ePorites\u003c/em\u003e populations could remain stable under future climates \u003csup\u003e18,21\u003c/sup\u003e. However, both communities\u0026rsquo; slowed tissue recovery and increased dissolution under OA highlight the importance of considering the potential ecological interactions arising under future climate conditions.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTurf-algal associated biological activity was assessed through microenvironment O\u003csub\u003e2\u003c/sub\u003e profiles, which showed that O\u003csub\u003e2\u003c/sub\u003e concentrations beneath the turf algal mat had high diel oxic fluctuations. For instance, this ranged from hyperoxic in the light (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;sd; 757.85\u0026thinsp;\u0026plusmn;\u0026thinsp;484.04 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) to hypoxic in the dark (34.43\u0026thinsp;\u0026plusmn;\u0026thinsp;36.81 \u0026micro;mol L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e; Supplementary Table\u0026nbsp;3 and Supplementary Fig.\u0026nbsp;5) under high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions. Turf-associated respiration was assessed by measuring the apparent O\u003csub\u003e2\u003c/sub\u003e consumption rates within the turf algal mat (0\u0026ndash;50 \u0026micro;m above exposed coral skeleton) in the dark. These rates did not differ across either genera of coral-turf algae communities (\u003cem\u003eAcropora\u003c/em\u003e: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,12\u003c/sub\u003e = 0.92, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.337; \u003cem\u003ePorites\u003c/em\u003e: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,12\u003c/sub\u003e = 0.64, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.423; Supplementary Table\u0026nbsp;4), suggesting biological activity remained constant.\u003c/p\u003e \u003cp\u003eIncreased O\u003csub\u003e2\u003c/sub\u003e concentration under light corresponded with pH levels higher than bulk seawater pH regardless of \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions at both the coral tissue and turf-covered exposed coral skeleton surface (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b and Supplementary Fig.\u0026nbsp;5). In the dark, the observed pH on both the coral tissue surface (\u003cem\u003eAcropora\u003c/em\u003e: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,24\u003c/sub\u003e = 6.6, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.01, \u003cem\u003ePorites\u003c/em\u003e: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,16\u003c/sub\u003e = 6.72, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.01) and on the turf-covered coral skeleton (Combined: \u003cem\u003ex\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003csub\u003e1,40\u003c/sub\u003e = 9.54, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.002; Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, b and Supplementary Table\u0026nbsp;2) was significantly reduced under high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions compared to present-day conditions. This led to a decrease in Ω\u003csub\u003earagonite\u003c/sub\u003e on the surface of the coral tissue surface from 3.04\u0026thinsp;\u0026plusmn;\u0026thinsp;0.94 to 0.93\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4 (mean\u0026thinsp;\u0026plusmn;\u0026thinsp;sd) and on the surface of the exposed coral skeleton beneath the turf algal mat from 4.13\u0026thinsp;\u0026plusmn;\u0026thinsp;1.79 to 0.75\u0026thinsp;\u0026plusmn;\u0026thinsp;0.28 (Supplementary Table\u0026nbsp;3).\u003c/p\u003e \u003cp\u003eWe interpreted these diel changes in O\u003csub\u003e2\u003c/sub\u003e and pH as high daytime photosynthetic production of dissolved organic carbon exudates \u003csup\u003e22\u003c/sup\u003e and subsequent consumption by copiotrophs \u003csup\u003e14\u003c/sup\u003e. As O\u003csub\u003e2\u003c/sub\u003e consumption rates remaining constant across \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions, we can infer that the turf-associated biological activity does not directly benefit from OA; rather, that dissolution is thermodynamically favored (i.e. Ω\u003csub\u003earagonite\u003c/sub\u003e\u0026thinsp;\u0026lt;\u0026thinsp;1) only when the biological activity of the turf algal mat is combined with elevated \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThe negative effects of OA on coral skeletal growth are typically greater under dark conditions \u003csup\u003e23,24\u003c/sup\u003e, suggesting live coral calcification within the coral-turf algae communities would have been decreased in our experiments. Despite the coral tissue surface exhibiting undersaturation values of Ω\u003csub\u003earagonite\u003c/sub\u003e, the skeleton microstructure beneath it showed typical morphological features with no signs of degradation or dissolution under high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec-f and Supplementary Figs.\u0026nbsp;6\u0026ndash;8). This suggests a form of compensatory mechanism to upregulate the pH at the calcification site \u003csup\u003e25\u003c/sup\u003e. Turf-covered skeletons were visibly degraded in both \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eg-j and Supplementary Figs.\u0026nbsp;6\u0026ndash;8) suggesting turf algae as the main driver for the reduction of net community calcification and accretion rates. In addition, the turf-covered skeletal portion of \u003cem\u003ePorites\u003c/em\u003e coral-turf communities showed potential signs of diagenesis in the form of aragonite needles \u003csup\u003e26\u003c/sup\u003e under high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ej). The combined effects of turf algal driven local acidification and OA shift the community\u0026rsquo;s CaCO\u003csub\u003e3\u003c/sub\u003e productivity towards dissolution, thereby contributing to the ongoing bioerosion of reefs.\u003c/p\u003e \u003cp\u003eOur findings emphasize that coral-turf algae interactions under future elevated \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions will accelerate the degradation of coral ecosystems and alter their function. The role of turf algae in driving bioerosion is seldom investigated under present and future climate conditions \u003csup\u003e13\u003c/sup\u003e. As turf algal growth and prevalence is expected to increase under OA \u003csup\u003e4,10,27\u003c/sup\u003e, its role as a bioeroder should be integrated into current end-of-the-century global accretion models \u003csup\u003e13\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e\u003cem\u003eAquaria experiment setup\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAquaria experiment tanks were continuously supplied with fresh unfiltered seawater pumped from a depth of 2 and 5 m from a nearby bay in front of the Tropical Biosphere Research Center (Sesoko island, Okinawa, Japan;\u0026nbsp;26\u0026deg; 38\u0026apos; 13\u0026quot; N 127\u0026deg; 51\u0026apos; 53\u0026quot; E) and the Shimoda Marine Research Center (Shimoda city, Japan; 34\u0026deg; 39\u0026apos; 57\u0026quot; N 138\u0026deg; 56\u0026apos; 20\u0026quot; E; Supplementary Fig. 1 and Table 1). Each experimental tank (length \u0026times; width \u0026times; height; Sesoko: 3.5 L, 20 \u0026times; 15 \u0026times; 15 cm; Shimoda: 16 L, 30 \u0026times; 20 \u0026times; 30 cm) was continuously aerated, with aquarium lights (ZetLight\u003csup\u003e\u0026copy;\u003c/sup\u003e Lancia2 Series, USA) maintained at\u0026nbsp;5.01 \u0026plusmn; 1.43\u0026nbsp;mol photons m\u003csup\u003e2\u0026nbsp;\u003c/sup\u003es\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003efor 12 hours each day. Each tank was outfitted with a pH and temperature sensor (Neptune Systems, USA), logging real-time measurements every five minutes. In order to control pH within experimental tanks, CO\u003csub\u003e2\u003c/sub\u003e was bubbled using a fine air stone (LSS Laboratory, Japan) controlled by both a solenoid and needle valve (LSS Laboratory, Japan). The solenoid valve, which controls opening and closing periods, was maintained using an APEX aquarium system (Neptune Systems, USA), which was also used for measurement and logging of the real-time pH and temperature of all tanks. Two \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions were chosen for all aquaria experiments: a present-day \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition with ambient unfiltered natural seawater, and a high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition maintained at 7.85 pH in accordance with the SSP5-8.5 scenario\u003csup\u003e1\u003c/sup\u003e. Each tank\u0026rsquo;s respective pH value was corrected based on a pH reading measured using a multi-sensor (ThermoScientific\u0026trade; Orion Star\u0026trade; A326, USA). Using pH values from the in-tank pH sensor and stand-alone multi-sensor, we calculated the difference and corrected the pH value in which the CO\u003csub\u003e2\u003c/sub\u003e solenoid valve would open and close, allowing us to set up the APEX pH system accurately. All experimental aquaria tanks had a small aquarium corner pump to induce water movement (GEX, Japan).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCoral preparation\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe Shimoda aquaria (\u003cem\u003en\u003c/em\u003e = 10) and Shikine island transplantation (\u003cem\u003en\u003c/em\u003e = 6) experiments both used \u003cem\u003eAcropora solitaryensis\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e and \u003cem\u003ePorites heronensis\u003c/em\u003e\u003csup\u003e3\u003c/sup\u003e, which were sampled at Shikine island (Tokyo Prefecture, Japan, 34\u0026deg; 19\u0026apos; 34\u0026quot; N 139\u0026deg; 12\u0026apos; 36\u0026quot; E) and at Shimoda city (Shizuoka Prefecture, Japan, 34\u0026deg; 39\u0026apos; 58.1\u0026quot; N 138\u0026deg; 56\u0026apos; 33.6\u0026quot; E), respectively (Supplementary Fig. 1 and Supplementary Table 1). The Sesoko aquaria experiment (\u003cem\u003en\u003c/em\u003e = 5) used \u003cem\u003eAcropora hyacinthus\u003c/em\u003e\u003csup\u003e4\u003c/sup\u003e and \u003cem\u003ePorites cylindrica\u003c/em\u003e\u003csup\u003e4\u003c/sup\u003e sampled at the bay in front of the Sesoko Research station (26\u0026deg; 38\u0026apos; 13\u0026quot; N 127\u0026deg; 51\u0026apos; 53\u0026quot; E; Supplementary Fig. 1\u0026nbsp;and Supplementary Table 1). To avoid potential genotype bias, coral colonies were sampled equivalent to their replicate number. Following sampling, each colony was split into two ~30 cm\u003csup\u003e2\u003c/sup\u003e sized microcolonies for each \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition (present-day, high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA)). All microcolonies had half of their tissue stripped using pressurized air, leaving behind bare coral skeleton. These half-and-half tissue and bare skeleton microcolonies were then acclimated for around a week in each of their respective environments (aquaria, field), where naturally present turf algae settled onto the bare skeleton portion. The Shimoda and Sesoko aquaria experiment durations were 111 (2021-10-12 to 2022-01-31) and 31 (2023-07-28 to 2023-08-28) days, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eField transplantation experiment setup\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe field transplantation experiment was conducted at Shikine island (Tokyo Prefecture, Japan, 34\u0026deg; 19\u0026apos; 34\u0026quot; N 139\u0026deg; 12\u0026apos; 36\u0026quot; E), which is regarded as an analogue for ocean acidification (OA) due to its CO\u003csub\u003e2\u003c/sub\u003e seeps\u003csup\u003e5\u003c/sup\u003e. The experiment was conducted from 2022-08-12 to 2023-04-05 (236 days). Specimens were transplanted to two sites with differing \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions: a present-day site (Mikawa bay, mean \u0026plusmn; se, pH 8.26 \u0026plusmn; 0.001, pCO\u003csub\u003e2\u003c/sub\u003e 317.325 \u0026micro;atm) and a high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA) site (pH 7.832 \u0026plusmn; 0.003, pCO\u003csub\u003e2\u003c/sub\u003e 1005.173 \u0026micro;atm; Supplementary Fig. 1 and Supplementary Table 1) To fix specimens to each site, all microcolonies were epoxied (E380 underwater bonder, Konishi Company, Japan) onto ~8 \u0026times; 8 cm PVC tiles, which were subsequently attached to 30 cm long steel bars. Bars were set up using anchor bolts (8.5 mm width, 70 mm length) drilled into rock by SCUBA divers at ~8 m depth (Nemo Underwater Drill). Bars at both locations were deployed haphazardly within a \u003cem\u003ecirca\u003c/em\u003e 100 m\u003csup\u003e2\u003c/sup\u003e area, with a distance of ~5 m between each bar. Following retrieval of experimental specimens, they were incubated according to their respective \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions in the aforementioned aquaria tank system for physiological measurements and microsensor profiling. Environmental parameters at both sites were assessed during the experiment duration, with pH measurements taken \u003cem\u003ein situ\u003c/em\u003e using a pH logger (HOBO, USA), and seawater sampled for total alkalinity (\u003cem\u003en\u003c/em\u003e = 3) at both sites. Total alkalinity was measured using an automatic titrator (916 Ti-Touch, Metrohm AG, Switzerland), with details outlined in the following methods for measurements of net community calcification.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMeasurements\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eCompetition outcome\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eCompetition outcome was assessed by photographing each microcolony from a top-down angle at the beginning and end of each experiment and measuring the surface area of the live coral tissue and the portion of exposed coral skeleton covered with turf algae, using ImageJ\u003csup\u003e6\u003c/sup\u003e. Surface area was then converted as a percentage of total colony area and shown as a rate of change throughout the experimental duration (days).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAccretion rate\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAccretion rates were calculated using the buoyant weight technique\u003csup\u003e7\u003c/sup\u003e by measuring the weight of all microcolonies at the start and end of each experiment and shown as a rate of change throughout the experimental duration (days).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eNet community calcification\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eNet community calcification was measured using the alkalinity anomaly method\u003csup\u003e8\u003c/sup\u003e. We measured total alkalinity at the start and end of a 12 (Shimoda aquaria, Shikine transplantation) and 3 (Sesoko aquaria)-hour incubation period under both light and dark conditions at the end of all experiments. Prior to measurement, each microcolony was isolated into individual tanks. Following isolation, start samples (~50 mL seawater) were taken, seawater input was halted, with CO\u003csub\u003e2\u003c/sub\u003e and air still bubbling to maintain pH and oxygen levels over the extended incubation periods. Titration of total alkalinity samples was done using an automatic titrator (916 Ti-Touch, Metrohm AG, Switzerland), using 0.1 mol L\u003csup\u003e-1\u003c/sup\u003e HCl (Wako, Japan) as measurement solution. The pH electrode was calibrated on the total scale with Tris buffer in artificial seawater solution (Wako, Japan). Total alkalinity calculation was done using an R script adapted from the R package \u0026lsquo;seacarb\u0026rsquo;\u003csup\u003e9\u003c/sup\u003e. Alkalinity measurements were validated using a running standard consisting of aged seawater for which the total alkalinity was checked against CRM materials obtained from Dickson\u0026rsquo;s lab (batch number: 152) Net community calcification is shown as a rate of calcium carbonate (CaCO\u003csub\u003e3\u003c/sub\u003e) changedaily (12 hours light, 12 hours dark).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSurface area\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eSurface area measurements of all measured microcolony fragments were done using both the wax\u003csup\u003e10\u003c/sup\u003e and foil methods\u003csup\u003e11\u003c/sup\u003e. All microcolony fragments were first cleaned in a 0.1 mmol bleach solution, and subsequently dried at room temperature (~25 \u0026deg;C). Following this step, initial weight was measured (HR-60, A \u0026amp; D, Japan). Paraffin wax was melted at 60 \u0026deg;C in a container within a water bath (Smart Water Bath, AS ONE, Japan), and all samples were dipped and then shaken for three seconds each. Post and pre-wax weights were then standardized using the foil weights of a subset of colonies for each species.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eSEM micrography\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eFollowing the cleaning step used for surface area measurements, all samples were dried at 60\u0026deg;C in an oven and then desiccated in a vacuum chamber containing P\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e10\u003c/sub\u003e until completely dry. All samples were then placed into a tabletop SEM for imaging (JCM-5000 NeoScope\u0026trade; Tabletop SEM, Japan). Past literature was used to identify forms of diagenesis observed within our samples\u003csup\u003e12,13\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMicrosensor measurements\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMicrosensor tank setup\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eMicrosensor measurements were done within four days following the end of the Shimoda aquaria and Shikine island transplantation experiments. A 60 \u0026times; 25 \u0026times; 15 cm (length \u0026times; width \u0026times; height) acrylic flow-through tanks outfitted with flow straighteners on both sides of the measurement area were used for incubating microcolonies when taking microsensor measurements (Supplementary Fig. 9). We used a closed-system setup, filled with filtered natural seawater (0.2 \u0026micro;m cartridge filter, Advantec, Japan), with flowrate maintained at ~3 cm s\u003csup\u003e-1\u003c/sup\u003e, with water continuously aerated using an aquarium pump (Japan Pet Design, JET, Japan). An aquarium light (Radion G3, Ecotech Marine, USA) maintained at ~5 mol m\u003csup\u003e2\u0026nbsp;\u003c/sup\u003ed\u003csup\u003e-1\u0026nbsp;\u003c/sup\u003ewas used when conducting measurements for light settings. Dark settings were maintained by covering the entire system with a blackout sheet. For microsensor observation, we used a stereoscope (LabScope ZEISS, Sony, Japan) attached to a boom stand (SZ-STU1, Olympus, Japan), and was outfitted with a small lamp used when placing and lowering microsensors in dark settings.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMicrosensor setup and calibration\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eCoral and turf algae covered exposed coral skeleton oxygen concentrations (O\u003csub\u003e2\u003c/sub\u003e) were measured using a Clark-type O\u003csub\u003e2\u003c/sub\u003e glass microsensor (tip size of 40\u0026ndash;60 \u0026mu;m; Ox-50 Unisense A/S, Aarhus, Denmark). Calibration was done as follows: an O\u003csub\u003e2\u003c/sub\u003e zero reading was accomplished by preparing a sodium sulfite and filtered seawater solution at 0.1 M concentration (Na\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e3\u003c/sub\u003e, Nacalai Tesque, Japan) following the manufacturer\u0026rsquo;s instructions, an O\u003csub\u003e2\u003c/sub\u003e saturation state was accomplished by bubbling air into the filtered seawater using a simple air pump for at least 15 minutes. Coral and turf algae covered exposed coral skeletal surface pH was measured using pH glass microelectrodes (tip size of 40 - 60 \u0026mu;m; pH-50 Unisense A/S, Aarhus, Denmark). The microelectrode was connected to a reference electrode (Unisense A/S, Aarhus, Denmark). Calibration was done using standard NBS calibration buffer solution (pH 4, 7, 10; NIST Traceable Solutions, USA). Both microsensors were connected to the UniAmp Multi Channel (UniAmp Multi Channel; Unisense A/S, Aarhus, Denmark), which directly connected to a computer using the SensorTrace software, used for all microsensor measurements and profiling (SensorTrace Suite; Unisense A/S, Aarhus, Denmark). A dual-head manual micromanipulator (MM33-2; Unisense A/S, Aarhus, Denmark) was used to hold and control both microsensors simultaneously. The seawater within the microsensor measurement tank was also logged using a multi-sensor (ThermoScientific\u0026trade; Orion Star\u0026trade; A326, USA) outfitted with a dissolved oxygen (DO) and pH/temperature sensor, as to ensure the accuracy and as an above-CBL (concentration boundary layer) comparison of the microsensor O\u003csub\u003e2\u0026nbsp;\u003c/sub\u003eand pH readings.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eMicrosensor profiles\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eCoral-turf algal communities from each \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition and species were chosen at random for pH (\u003cem\u003eAcropora\u003c/em\u003e Coral tissue: \u003cem\u003en\u003c/em\u003e = 12 per light and \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition, \u003cem\u003ePorites\u003c/em\u003e Coral Tissue: present-day: \u003cem\u003en\u003c/em\u003e = 10 per light condition, high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA): \u003cem\u003en\u003c/em\u003e = 6 (Light) \u0026amp;\u003cem\u003e\u0026nbsp;n\u003c/em\u003e = 7 (Dark), Turf algae: \u003cem\u003en\u003c/em\u003e = 24 per light and \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition) and O\u003csub\u003e2\u003c/sub\u003e (\u003cem\u003eAcropora\u003c/em\u003e \u0026amp; \u003cem\u003ePorites\u0026nbsp;\u003c/em\u003eCoral tissue:\u003cem\u003e\u0026nbsp;n\u0026nbsp;\u003c/em\u003e= 6 per light and \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition, Turf algae:\u003cem\u003e\u0026nbsp;n\u0026nbsp;\u003c/em\u003e= 12 per light and \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition) microsensor profiling (Supplementary Table 2). Measurements from the Shimoda aquaria and Shikine island transplantation experiments were pooled for pH data, whereas O\u003csub\u003e2\u0026nbsp;\u003c/sub\u003edata is only from the Shimoda experiment. Microsensor depth profiles were taken in both light and dark settings at four points (two measurements per location) on each microcolony: (1) coral tissue and (2) turf algae covered exposed coral skeleton (Supplementary Fig. 10). All colonies were acclimated for at least one hour to their respective light and \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions prior to measurements. Before measuring depth profiles for each measurement, pH and O\u003csub\u003e2\u003c/sub\u003e readings above the concentration boundary layer (CBL) were noted. Depth profiles began at the surface for each measurement location (Coral tissue: on the coral tissue, Turf algae: on the exposed coral skeleton underneath the turf algae), with one measurement taken every 10 \u0026mu;m until pH and O\u003csub\u003e2\u003c/sub\u003e had returned to tank (above-CBL) values. Following each measurement profile, both sensors were washed using filtered seawater to strip off potentially attached turf algae and mucus. Tank seawater was changed after conducting all measurements of one coral colony. All profiled coral-turf algae community colonies were orientated the same, with turf algae on the downstream of living coral tissue, to avoid CBL-induced differences on the coral tissue via turf algae influence (Supplementary Fig. 10).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eData analyses\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eAll figures were generated with R software v4.2.2\u003csup\u003e14\u003c/sup\u003e. We used \u0026lsquo;ggplot2\u0026rsquo;, \u0026lsquo;forcats\u0026rsquo;, \u0026lsquo;dplyr\u0026rsquo;, \u0026lsquo;tibble\u0026rsquo; and \u0026lsquo;scales\u0026rsquo; packages from the \u0026lsquo;tidyverse\u0026rsquo;\u003csup\u003e15\u003c/sup\u003e, \u0026lsquo;ggpubr\u0026rsquo;\u003csup\u003e16\u003c/sup\u003e, \u0026lsquo;rstatix\u0026rsquo;\u003csup\u003e17\u003c/sup\u003e, \u0026lsquo;ggsignif\u0026rsquo;\u003csup\u003e18\u003c/sup\u003e and \u0026lsquo;patchwork\u0026rsquo;\u003csup\u003e19\u003c/sup\u003e packages for all figure production and data analysis. Figures containing photo panels were created using the Inkscape graphics editing software\u003csup\u003e20\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eCompetition outcome, accretion rates, net community calcification rates, and pH microsensor profile data were assessed using a linear mixed model (lmm) using the function \u0026lsquo;lmer\u0026rsquo; from the package \u0026lsquo;lme4\u0026rsquo;\u003csup\u003e21\u003c/sup\u003e for the model, and \u0026lsquo;Anova\u0026rsquo; for the subsequent test from the package \u0026lsquo;car\u0026rsquo;\u003csup\u003e22\u003c/sup\u003e. For each model, data from all experiments was pooled, and our fixed factor was \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition (fixed factor with two levels: present-day, high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA)) for each coral-turf algae genera (\u003cem\u003eAcropora\u003c/em\u003e, \u003cem\u003ePorites\u003c/em\u003e), with \u003cem\u003eExperiment\u003c/em\u003e as the random factor (Shimoda, Shikine, Sesoko). Comparisons between mean values (dashed lines) of both \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions across each \u003cem\u003eExperiment\u003c/em\u003e (Red: Shimoda, Green: Shikine, Blue: Sesoko) was plotted together with the predicted mean values (solid lines) from our linear mixed model for both \u003cem\u003eAcropora\u003c/em\u003e and \u003cem\u003ePorites\u003c/em\u003e coral-algae communities for competition outcome, accretion rates and net community calcification rates (Supplementary Figure 4).\u003c/p\u003e\n\u003cp\u003eFor pH microsensor profiles, the lowest measurement (Depth = 0 \u0026micro;m), being the surface of the coral tissue and exposed skeleton underneath the turf algae values (Coral tissue, Turf algae) were tested for both for the coral tissue of \u003cem\u003eAcropora\u003c/em\u003e and \u003cem\u003ePorites\u003c/em\u003e and turf algae from both genera undertwo light conditions (Light, Dark). For models that showed significance, we validated our models by first comparing the AIC (Akaike information criteria) scores following an analysis of variance (\u0026lsquo;anova\u0026rsquo; function) between models with and without the fixed factor of \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition (Supplementary Table 2). Following this, we used the function \u0026lsquo;performance\u0026rsquo; from the package \u0026lsquo;performance\u0026rsquo;\u003csup\u003e23\u003c/sup\u003e to produce a set of indices describing the model fit (Supplementary Table 2). The scores (AIC, AICc, BIC (Bayesian information criterion), R2 conditional, R2 marginal, ICC (Intraclass correlation), RMSE (Root-mean square deviation), Sigma) suggest the pooling and subsequent usage of \u003cem\u003eExperiment\u003c/em\u003e as a random factor are adequate based on similar methods described in previous studies\u003csup\u003e24,25\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe diffusive oxygen fluxes between 0 and 50 \u0026micro;m above the exposed coral skeleton beneath the turf algal mat were calculated using Fick\u0026rsquo;s first law assuming a flat surface without substantial heterogeneity and following K\u0026uuml;hl et al\u003csup\u003e26\u003c/sup\u003e:\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003c/p\u003e\n\u003cp\u003ewith the O\u003csub\u003e2\u003c/sub\u003e diffusion constant D = 2.35 mol cm\u003csup\u003e2\u003c/sup\u003e s\u003csup\u003e-1\u003c/sup\u003e (25 \u0026deg;C and 35 \u0026permil; salinity seawater), \u0026Delta;[O\u003csub\u003e2\u003c/sub\u003e] the difference between the O\u003csub\u003e2\u003c/sub\u003e concentrations at the surface of the turf-covered exposed skeleton surface (0 \u0026micro;m) and the one at 50 \u0026micro;m above, \u0026Delta;x = 0.0050 cm. The diffusion constant was not corrected for porosity and tortuosity\u003csup\u003e27\u003c/sup\u003e with the assumption that it would be similar in both treatments.\u003c/p\u003e\n\u003cp\u003eOxygen flux values were compared using Kruskal-Wallis tests, with \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e condition as \u0026nbsp;fixed factor (with two levels: present-day, high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e (OA)) and compared for each coral-turf algae genera (\u003cem\u003eAcropora\u003c/em\u003e, \u003cem\u003ePorites\u003c/em\u003e) and light condition (Light, Dark) (Supplementary Table 4).\u003c/p\u003e\n\u003cp\u003eThe seawater saturation state of aragonite (Ω Aragonite) of the surface of the coral tissue and sub-turf algal layer\u0026rsquo;s microchemical environment was calculated from pH microsensor profiles together with the seawater temperature and the total alkalinity of the microsensor holding tank using the excel calculator program \u0026lsquo;CO2SYS\u0026rsquo;\u003csup\u003e28\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReferences for methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e1.\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Calvin, K. et al. IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland. https://www.ipcc.ch/report/ar6/syr/ (2023) doi:10.59327/IPCC/AR6-9789291691647.\u003c/p\u003e\n\u003cp\u003e2.\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Veron, JEN. \u0026amp; Wallace, CC. Scleractinia of Eastern Australia \u0026ndash; Part V. Family Acroporidae. Aust. Inst. Mar. Sci. Monogr. Ser. \u003cstrong\u003e6\u003c/strong\u003e, 1\u0026ndash;485 (1984).\u003c/p\u003e\n\u003cp\u003e3.\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Veron, JEN. New Scleractinia from Australian coral reefs. Rec. West. Aust. Mus. \u003cstrong\u003e12\u003c/strong\u003e, 147\u0026ndash;183 (1985).\u003c/p\u003e\n\u003cp\u003e4.\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Dana, J. D. 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Section 8 update: Use of microelectrodes to measure in situ microbial activities in biofilms, sediments, and microbial mats. in Molecular Microbial Ecology Manual (eds. Kowalchuk, G. A., De Bruijn, F. J., Head, I. M., Akkermans, A. D. \u0026amp; Van Elsas, J. D.) 3483\u0026ndash;3514 (Springer Netherlands, 2008). doi:10.1007/978-1-4020-2177-0_802.\u003c/p\u003e\n\u003cp\u003e28.\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;Pierrot, D., Lewis, E. \u0026amp; Wallace, D. MS Excel Program Developed for CO2 System Calculations ORNL/CDIAC-105, Carbon Dioxide Inf. Anal Cent Oak Ridge Natl Lab U Dept Energy Oak Ridge Tenn Httpscdiac Ess-Dive Lbl Govftpco2sysCO2SYScalcXLSv2 \u003cstrong\u003e1\u003c/strong\u003e, (2006).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis project contributes towards the International CO\u003csub\u003e2\u003c/sub\u003e Natural Analogues (ICONA) Network. The authors would like to acknowledge the technical staff (Manabu Ooue, Jiro Takano, Daisuke Shibata, Toshihiko Sato, Chika Nakamura) of the Shimoda Marine Research Center (University of Tsukuba) for assistance in sampling and transplantation of corals in the field. The authors also thank the students and faculty at the Shimoda Marine Research Center and the Sesoko Station for their role in discussing the results of this study. Thank you to Dr. Shunsuke Yaguchi for assistance with preparation and analysis of samples using the SEM. Special thanks to Kayo Takonai (lab technician) who assisted in processing and analyzing total alkalinity samples.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was partially funded by the JST SPRING grant (Grant Number JPMJSP2124 2021) and was partially funded by the Japan Society for the Promotion of Science (JSPS) Core-to-Core Program (Grant Number: JPJSCCA20210006).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eJoshua M. Heitzman\u003c/strong\u003e: Conceptualization, Methodology, Formal analysis, Resources, Investigation, Data curation, Visualization, Writing - Original draft, Writing - Review \u0026amp; Editing, Funding acquisition\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eLayla Iijima\u003c/strong\u003e: Formal analysis, Investigation, Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eGuinther Mitushasi\u003c/strong\u003e: Formal analysis, Investigation, Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDavide Spatafora\u003c/strong\u003e: Formal analysis, Writing - Review \u0026amp; Editing\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eShigeki Wada\u003c/strong\u003e: Writing - Review \u0026amp; Editing, Funding acquisition\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eBen P. Harvey\u003c/strong\u003e: Writing - Review \u0026amp; Editing, Funding acquisition\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHaruko Kurihara\u003c/strong\u003e: Investigation, Resources, Writing - Review \u0026amp; Editing, Supervision\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSylvain Agostini\u003c/strong\u003e: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Visualization, Writing - Review \u0026amp; Editing, Project administration, Supervision, Funding acquisition\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eR code for figure production and raw data are available on the GitHub repository: https://github.com/joheitzman/OA_Turf\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eCalvin, K. et al. 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Sci. \u003cstrong\u003e7\u003c/strong\u003e, (2020).\u003c/li\u003e\n\u003cli\u003eGeorgiou, L. et al. pH homeostasis during coral calcification in a free ocean CO2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef. Proc. Natl. Acad. Sci. \u003cstrong\u003e112\u003c/strong\u003e, 13219\u0026ndash;13224 (2015).\u003c/li\u003e\n\u003cli\u003eBar-Matthews, M., Wasserburg, G. J. \u0026amp; Chen, J. H. Diagenesis of fossil coral skeletons: Correlation between trace elements, textures, and 234U238U. Geochim. Cosmochim. Acta \u003cstrong\u003e57\u003c/strong\u003e, 257\u0026ndash;276 (1993).\u003c/li\u003e\n\u003cli\u003eEnochs, I. C. et al. Ocean acidification enhances the bioerosion of a common coral reef sponge: implications for the persistence of the Florida Reef Tract. Bull. Mar. Sci. \u003cstrong\u003e91\u003c/strong\u003e, 271\u0026ndash;290 (2015).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-3779657/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-3779657/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTurf algal prevalence will increase in coral ecosystems under ocean acidification yet their contribution towards the ongoing and projected degradation of reefs is often overlooked. \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eTurf algal settlement was induced on exposed coral skeleton adjacent to live coral tissue to investigate coral-turf algal interactions through a combination of laboratory and field transplantation (shallow volcanic CO\u003c/span\u003e\u003csub\u003e\u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003e2\u003c/span\u003e\u003c/sub\u003e \u003cspan type=\"SmallCaps\" class=\"SmallCaps\" name=\"Emphasis\"\u003eseep) experiments across two temperature regimes.\u003c/span\u003e Here, we show that turf algae are competitively favored over corals under high \u003cem\u003ep\u003c/em\u003eCO\u003csub\u003e2\u003c/sub\u003e conditions. Turf algae-associated biological activity locally acidified the microenvironment overlying the exposed coral skeleton, leading to its bioerosion. Increases in coral-turf algal interactions could shift coral ecosystems towards net dissolution and should be integrated into global accretion models when considering future carbonate budgets under climate change.\u003c/p\u003e","manuscriptTitle":"Turf algae drives coral bioerosion under high CO2","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-01-25 17:52:21","doi":"10.21203/rs.3.rs-3779657/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"communications-earth-and-environment","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"commsenv","sideBox":"Learn more about [Communications Earth and Environment](https://www.nature.com/commsenv/)","snPcode":"","submissionUrl":"","title":"Communications Earth \u0026 Environment","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Communications Series","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"1ee63912-c1ee-4545-89f9-bd081a340978","owner":[],"postedDate":"January 25th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":28084947,"name":"Earth and environmental sciences/Ocean sciences/Marine biology"},{"id":28084948,"name":"Earth and environmental sciences/Ecology/Climate-change ecology"}],"tags":[],"updatedAt":"2024-01-25T17:52:21+00:00","versionOfRecord":[],"versionCreatedAt":"2024-01-25 17:52:21","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-3779657","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-3779657","identity":"rs-3779657","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}