Complex food sources aid physiological compensation of bleached corals

Complex food sources aid physiological compensation of bleached corals | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Complex food sources aid physiological compensation of bleached corals María Antonieta López, Lea Hiemer, Marie Engel, Maren Ziegler This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6767958/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 10 Mar, 2026 Read the published version in Marine Biology → Version 1 posted 5 You are reading this latest preprint version Abstract Climate change induced coral bleaching threatens the survival of coral reefs. The disruption of the symbiosis between corals and their photosymbionts during bleaching inhibits photosynthesis, the main source of energy of the coral holobiont. Yet, corals can supplement their metabolic demand through heterotrophic feeding and may partially compensate for the lack of autotrophic energy. However, the potential of different types of heterotrophic food to compensate for productivity loss during bleaching is not yet known. Therefore, we evaluated the effect of different food types on the physiology of symbiotic and bleached corals of three species ( Galaxea fascicularis , Porites lobata , and Stylophora pistillata ). Symbiotic and bleached fragments were exposed to five feeding treatments in a 21-week aquarium experiment that included combinations of dissolved and particulate feeds composed of thawed plankton, Artemia salina nauplii, three phytoplankton species, honey, yeast, and amino acids. Here we show that in symbiotic G. fascicularis and P. lobata , growth was not affected by the different food types, while growth increased 1.5- to 2-fold in the high complexity feed in symbiotic S. pistillata . In contrast, all bleached corals benefitted from richer diets. Complex feeds doubled to tripled growth parameters relative to dissolved or low-complexity feeds, and bleached S. pistillata fragments fed only thawed plankton perished. Food treatments did not alter respiration or photosynthetic rates, indicating that growth gains stemmed from enhanced heterotrophic nutrient supply. Physiological rates were consistently higher in symbiotic fragments than in their bleached clones across all species and the differences increased with the baseline productivity of the species from G. fascicularis over P. lobata to S. pistillata . However, the food treatments did not have a clear effect on the differences between bleached and symbiotic fragments. Our results demonstrate that incorporating diverse particulate and dissolved feed components into restoration, aquaculture, or field supplementation protocols could bolster coral resilience to the increasing frequency of mass-bleaching events. Coral bleaching coral physiology heterotrophic feeding Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Coral reefs are highly productive ecosystems that provide an essential basis for marine biodiversity (Moberg & Folke, 1999), supporting up to a third of all marine animal and plant species, despite energy 100%covering only about 0.15% of the ocean surface (Roberts et al., 2002). As a result of prolonged and more severe marine heatwaves, recurrent coral bleaching events are threatening coral reefs around the world (Eakin et al., 2022; T. P. Hughes et al., 2018). Coral bleaching refers to the loss of the symbiotic unicellular dinoflagellate microalgae of the Symbiodiniaceae family from coral tissue, where they provide most of their energetic needs through photosynthesis (Gates et al., 1992; Muscatine & Cernichiari, 1969). The loss of the Symbiodiniaceae disrupts the main energy acquisition pathway for the corals which alters physiology from growth to reproduction, leads to tissue loss, and ultimately the death of the host (Agostini et al., 2013; Baird & Marshall, 2002; Hoegh-Guldberg et al., 2007). In addition to autotrophic energy acquisition through their symbiosis with microalgae, scleractinian corals complement their energetic needs through heterotrophic feeding (Lewis & Price, 1975). The expansion and movement of their polyps and tentacles allows them to swirl the water, filter out or catch prey, and digest it (Price & Patterson, 2023). Under normal conditions, it is assumed that heterotrophy supplies stony corals with vital nutrients that cannot be sufficiently provided via their photoautotrophic symbionts, such as phosphate and nitrogen (Houlbrèque & Ferrier-Pagès, 2009; Muscatine et al., 1984). Heterotrophic supplementation has positive effects primarily on the calcification rate, tissue growth, respiration as well as on chlorophyll density and photosynthetic rate (Houlbrèque & Ferrier-Pagès, 2009; Prézelin, 1987; Swanson & Hoegh-Guldberg, 1998). During coral bleaching, the capacity to meet the nutritional requirements through heterotrophic feeding becomes essential for survival (Houlbrèque & Ferrier-Pagès, 2009; Hughes & Grottoli, 2013). Corals with higher heterotrophic plasticity are able to maintain higher energy reserves (Grottoli et al., 2006; Rodrigues & Grottoli, 2007) and are more resistant to and recover faster from heat stress (Borell et al., 2008; Connolly et al., 2012; Grottoli et al., 2006). Heterotrophic plasticity, i.e. the flexibility in how and how much an organism relies on consuming organic matter rather than on autotrophy to survive and grow, varies among coral species and colonies of the same species (Grottoli et al., 2006; Hoogenboom et al., 2010). While some coral species maintain a fixed feeding strategy regardless of environmental fluctuations, limiting their stress tolerance, others exhibit higher trophic plasticity, shifting their feeding mode along the autotrophy-heterotrophy spectrum (Sturaro et al., 2021). The ability to switch between autotrophic and heterotrophic feeding in response to environmental conditions may explain why some coral species are more resilient to changing variables (e.g., increasing depth, turbidity) or stressors (e.g., heat) (Anthony & Fabricius, 2000; Grottoli et al., 2006; Swain et al., 2016). Not only heterotrophic plasticity, but also the specific type of food, may be critical for maintaining energy reserves and supporting key physiological functions such as growth and reproduction of healthy corals. For example, Craggs et al. (2017) successfully induced spawning in four Acropora species for the first time in a closed mesocosm system using a complex diet that included amino acids, picoplankton, nanoplankton, microplankton, mesoplankton, baker’s yeast, and microalgae. Similarly, Osinga et al. (2011) demonstrated that feeding with Artemia significantly enhanced the growth of Seriatopora caliendrum and Zaidi et al. (2023) reported that Acropora digitifera corals fed with Artemia and Budu (a fermented anchovy extract) exhibited higher growth and survival rates compared to unfed controls. However, the potential of different food types to compensate for productivity loss in bleached corals has never been investigated systematically. Therefore, the main goal of this study was to investigate the influence of heterotrophic nutrition on the physiology of scleractinian corals and evaluate the potential of different food types to compensate for productivity losses in bleached vs. symbiotic corals. The specific goals were to investigate the effects of different food types on: i) the physiology of symbiotic corals, ii) the physiology of bleached corals, and iii) the physiological compensation comparing symbiotic and bleached corals. To this end, we conducted a 21-week aquarium experiment, providing five food treatments of varying complexity composed of dissolved and particulate feeds to symbiotic and bleached fragments of the coral species Galaxea fascicularis (Linnaeus 1767), Porites lobata (Dana 1846), and Stylophora pistillata (Esper, 1792). We measured coral growth, photosynthesis, and respiration as proxies for physiological compensation. As the frequency and severity of bleaching events increases and the loss of coral cover is dramatic in all reef areas around the world, understanding the mechanisms that affect heterotrophic plasticity could shed light on acclimatization mechanisms and supplementation strategies that can contribute to survival of bleached corals. Materials and methods Experimental design The experiment was designed to investigate the influence of heterotrophic nutrition on the physiology of the three scleractinian coral species Galaxea fascicularis , Porites lobata and Stylophora pistillata in their symbiotic and bleached conditions. The experiment consisted of five treatments combining dissolved and particulate food types: thawed red plankton, freshly-hatched Artemia salina nauplii, three microalgae species, honey, yeast, and amino acids that were used to feed the corals over a 18-week period. (Fig. 1 ). Each of the five treatments was triplicated with a total of 15 × 40-L tanks. The tanks were part of a 3,000-L water recirculation system, and each experimental tank had a separate water inlet and outlet with a water exchange of 20 L h − 1 . The equipment per tank consisted of a wavemaker pump (easyStream pro ES-28, Aqualight GmbH, Bramsche/Lappenstuhl, Germany), a titanium heater to maintain the temperature between 26 and 27°C (Schego Heater 300 W, Schemel & Goetz GmbH, Germany), and four LED light strips with photosynthetically active radiation (PAR) between 140 and 190 µmol photons m − 2 s − 1 a light-dark cycle of 10:14 hours. The coral fragments were suspended on three plastic rods in each tank (Fig. S1 ). Coral species and replication For the experiment, three coral colonies of each of the species Galaxea fascicularis , Porites lobata , and Stylophora pistillata were sourced from the Ocean2100 coral aquarium facility of the Justus Liebig University Giessen, Germany (Tab. S1). The colonies were fragmented (3–8 cm length) using a hammer and chisel, and allowed to heal for eight weeks before starting the experiment. Thirty fragments per colony, 90 fragments per species (of which half were bleached), and 270 fragments in total were used. The fragments were evenly distributed in the tanks and treatments, resulting in 18 fragments, six per species with two fragments per colony (one symbiotic and one bleached), per tank. Menthol bleaching After eight weeks of acclimation, the coral fragments were randomly divided into two groups, which contained half of the coral fragments per genotype (15 fragments per genotype, 45 fragments per group per species). To chemically bleach the corals, we followed the protocols modified by Wang et al. (2012) and Bauer et al. (in preparation). Briefly, the bleaching consists of three days of treatment with 0.38 mM menthol in filtered (65 µm) seawater, followed by one day of rest and another day of menthol treatment. Menthol incubations lasted 8 h during the light period (Puntin, Wong, et al., 2023). Menthol bleaching was repeated for two days when corals started to regain color during the experiment. S. pistillata was rebleached once after 9 weeks, G. fascicularis was rebleached twice after 9 and 13 weeks, and P. lobata was rebleached five times after 6, 9, 12, 14, and 16 weeks. Feeding Coral fragments were fed with one of five food options combining dissolved and particulate food types: red plankton, Artemia salina nauplii, three microalgae species, honey, yeast, and an amino acid mixture (Table 1 ). The choice of these types of food was based on their nutritional value i.e., sources of carbon and nitrogen, and their beneficial effects on coral physiology, i.e., increased growth, up-regulation of photosynthesis (Craggs et al., 2017; Ferrier, 1991; Houlbrèque & Ferrier-Pagès, 2009; Osinga et al., 2011; Zaidi et al., 2023). Table 1 Information on the components and concentrations of the food treatments supplied to three stony coral species every day for three hours over an 18-week period. Food components [Concentration] Thawed plankton Dissolved food Low complexity Medium complexity High complexity Amino acids [0.025 µl ml − 1 ] ✓ ✓ Dry yeast [3,200 cells ml − 1 ] ✓ ✓ Honey [20 µg ml − 1 ] ✓ ✓ Microalgae: Tisochrysis lutea , Chaetoceros calcitrans, Tetraselmis chui [5,000 cells ml − 1 per species] ✓ ✓ Artemia salina nauplii [0.4 µg wet weight ml − 1 ] ✓ ✓ ✓ Thawed plankton [0.4 µg wet weight ml − 1 ] ✓ The following concentrations were applied for each composite of the food types: 0.025 µl ml − 1 of amino acid mixture (Pohl's Xtra special, Korallenzucht.de Vertriebs GmbH, Germany) was used. Amino acids dissolved in water are a natural source of nitrogen for stony corals (Ferrier, 1991). 0.03 g of dry baker's yeast (REWE supermarket, Germany) was used resulting in 3,200 cells ml − 1 . For each feeding tank, the dry yeast was weighed on a precision balance (Kern KB 360-3N, KERN & Sohn GmbH, Germany, precision: 0.001 g). and dissolved with water from the aquarium system. Dry yeast is a source of carbon and nitrogen, proteins, B-vitamins, pigments and complex carbohydrates, such as glucans and has been used in experiments with stony corals as a supplementary diet (Craggs et al., 2017). Organic honey (REWE supermarket, Germany) was supplied at 20 µg ml − 1 . The honey was weighed and mixed with water from the facility before addition to the tanks. The usage of honey as a feeding option for corals to bolster their health has been explored among coral hobbyists and aquarists (Sebastian, 2017). One gram of honey contains about 0.32 g of carbon. Three species of microalgae were used: Tetraselmis chui (Chlorophyte, 10 to 25 µm diameter, Montoya et al., 2024), Chaetoceros calcitrans (Diatom, 5 to 10 µm, De La Peña et al., 2018), and Tisochrysis lutea (Haptophyte, 3 to 7.5 µm, Heimann & Huerlimann, 2015) at a concentration of 5000 cells ml − 1 (5 x 10 6 cells L − 1 ) each. T. lutea was grown in 0.1% sterile-filtered (0.22 µm) Walne's medium (aquacare-shop, Germany), while T. chui and C. calcitrans were grown in sterile-filtered Guillard's F/2 medium with 0.1% silicate added to the medium for C. calcitrans. Microalgal cultures were maintained at 20–21°C, 47 µmol photon m − 2 s − 1 µmol, and a light cycle of 12 hours. The cell count was determined daily from the cultures using a Thoma hemocytometer. The corresponding volumes of the microalgae cultures were then centrifuged twice at 3,000 g for 10 min and resuspended in 50 ml seawater to wash out the medium. Depending on the algae species, the nutritional composition of lipids and carbohydrates may vary, but all have high levels of protein and essential fatty acids, as well as being good sources of ascorbic acid and riboflavin (Brown et al., 1997). Additionally, microalgae are a source of carbon for corals, which is used by both symbiotic and aposymbiotic corals (Leal et al., 2014). 0.8 g of wet mass of freshly hatched Artemia salina nauplii (prepared 24 hours before the feeding, 400–500 µm length) was used, which corresponds to approximately 22,000 nauplii L − 1 . Artemia salina nauplii are a source of nitrogen, carbon, carbohydrates, lipids and proteins and they are frequently used by aquarists and researchers to feed corals (Zaidi et al., 2023). 0.8 g of thawed red plankton (1000–2000 µm length) (Calanoide Copepoden, Zooschatz, Germany), resulting in approximately 1,000 organisms L − 1 . Frozen food was thawed, thoroughly rinsed in a sieve, and mixed with seawater from the aquarium system before addition to a feeding tank. The red plankton consists mainly of marine copepods, micronized shrimp larvae, seawater rotifers and salmon oil, and is a second standard feed in coral aquaculture. Each feeding tank was filled with 20 L of seawater, which was taken from the experimental aquarium system and roughly filtered (65 µm filter). Additionally, each tank was equipped with a pump for water circulation and a heater to maintain the temperature between 26 and 27°C. Feeding lasted three hours around dusk, i.e., it started 1.5 hours before the lights were turned off and took place at a light intensity about 10 µmol photons m − 2 s − 1 corresponding to a twilight phase. Physiological measurements To assess the effects of the different food types on the coral holobiont and photosymbiont physiology, we measured coral growth, photosynthesis and respiration rates after three weeks of feeding and after 18 weeks of feeding. Coral growth As proxies of coral growth, changes in calcification, volume growth, and surface area growth were used as a holobiont response to the food options. Calcification was measured following the buoyant-weighing method (Davies, 1989). Briefly, an 8-L aquarium was filled up with seawater from the experimental system. Corals were weighed with a precision balance using an under-floor weighing hook of the balance (Kern KB 360-3N, KERN & Sohn GmbH, Germany, precision: 0.001 g). The temperature of the water was kept constant at 26 ± 0.5°C with a submersible heater and salinity at 35. Volume growth and surface area of each fragment were measured using 3D scanning. For this, a handheld 3D scanner (Artec Spider 3D, Artec 3D, Luxembourg) was used together with the scanning software Artec Studio 16 (Artec 3D, Luxembourg) following Reichert et al. (2016). Coral fragments were placed on an automatic turning table, positioned in a 80 x 80 x 80 cm sized macrophoto studio and scanned within 40–50 s from two angles in two full rotations. Scans of the corals resulted in image point clouds, from which polygon structures were constructed. Finally, models built for each fragment were exported as .obj files. Surface area and volume were calculated in MeshLab Visual Computing Lab-ISTI-CNR (v.1.3.4 Β, 2014) using the ‘compute geometric measures’ tool. Finally, growth rates were calculated as the difference between the measurements taken before the start of the feeding regimes and after 18 weeks of feeding at the end of the experiment. Calcification rate and volume growth were standardized to surface area. Photosynthesis and respiration rates Net photosynthesis, respiration, and gross photosynthesis of symbiotic corals and respiration of bleached corals were measured as change in oxygen concentrations during incubations in light and dark. Specifically, the corals were placed in airtight sealed 1-L incubation jars that were filled with seawater from the experimental system. Oxygen concentration was measured at the beginning and at the end of the 60-min incubation with an optical oxygen sensor connected to a hand-held multi-parameter probe (Multi 3620 IDS SET G, Xylem Analytics, Germany). Each incubation run included two control jars without corals to correct for biological activity in the seawater. Net photosynthesis and respiration were corrected with the change in oxygen in the controls and normalized to incubation volume, incubation time, and coral surface area. Gross photosynthesis was calculated as the sum of net photosynthesis and respiration. Statistical analyses Statistical analyses were conducted in R (R version 4.2.2, (R Core Team, 2022) using the graphical user interface ‘RStudio’ (Version 2022.12.0 + 353, RStudio Inc., USA). To obtain coral growth, we converted the values from buoyant weight to actual weight using the seacarb package (Gattuso et al., 2021). To test the effects of different food types on the physiology of symbiotic and bleached corals, we used linear mixed-effects models with treatment (five levels: thawed plankton, dissolved food, low complexity, medium complexity, high complexity) as fixed factor and coral colony as random factor. Individual models were constructed for each response variable and species. The models were fitted using the lme4 package (Bates et al., 2015) and residual distributions were tested for normality and heteroscedasticity. If necessary, data were log-transformed to meet test assumptions. Models were analyzed using a post hoc test from the ‘multcomp’ package (Hothorn et al. 2020) with Tukey comparison with ‘holm’ adjustment for multiple testing. Model specifications can be found in supplemental material (Tabs. S2-15). To test the magnitude of the differences between symbiotic and bleached corals between the different food types, we calculated Hedges’ g effect sizes within each feeding regime on raw data for each variable. Finally, all results were visualized using ‘ggplot2’ (Wickham, 2016). Results Coral growth rates Coral growth rates differed between species, with an approximately two- to three-fold higher calcification rate and ten-fold volume and tissue growth rates in symbiotic Stylophora pistillata compared to symbiotic Galaxea fascicularis and Porites lobata , which had similar growth rates to each other (Fig. 2 A-C; Tab. S2). Respiration rates of symbiotic P. lobata were significantly higher than of G. fascicularisi , and S. pistillata had intermediate respiration rates (Fig. 2 D). Growth was reduced in all bleached corals and S. pistillata still maintained significantly higher growth rates than G. fascicularis and P. lobata (Fig. 2 ). Bleached P. lobata had intermediate growth rates that were significantly higher than in bleached G. fascicularis . Respiration rates were similar between all species when bleached (Fig. 2 D). Effects of food types on the physiology of symbiotic corals In symbiotic corals, growth was not affected by the different food types in G. fascicularis and P. lobata (Fig. 3 , Tab. S3, S5). In S. pistillata , volume and surface growth significantly increased with food complexity, with the high complexity feed resulting in highest growth rates (Fig. 3 F, I, Tab. S7). Respiration rates of all species were comparable (range 10–30 µg O 2 cm − 2 h − 1 ) and largely unaffected by food types (Fig. 3 , Tab. S4, S6, S8). Similar to coral growth, photosynthetic rates in S. pistillata were approximately double that of G. fascicularis and P. lobata . Effects of food types on the physiology of bleached corals Calcification rate and volume and tissue growth rates in bleached S. pistillata were all approximately two-fold higher compared to G. fascicularis and P. lobata (Fig. 2 ; Tab. S2). In S. pistillata , growth parameters in the high complexity feed were two- to three-fold increased compared to all other food types, and all bleached fragments in the thawed plankton treatment died (Fig. 4 , Tab. S11). While no mortality was recorded in P. lobata , the pattern was largely similar to that of S. pistillata in volume and surface growth, but the medium complexity feed also performed better than the less complex feeds (Fig. 4 ). A similar trend, although not significant, was observed for G. fascicularis . Respiration rates of all bleached species were comparable (range 5–20 µg O 2 cm − 2 h − 1 ) and largely unaffected by food types (Fig. 4 , Tab. S12). Effect of food types on heterotrophic compensation Metabolic rates were consistently higher in symbiotic fragments than in their bleached clones across all species (Fig. 5 ). The food treatments did not have a clear effect on the differences between bleached and symbiotic fragments in any of the species. Differences were smallest in G. fascicularis , in which the growth and respiration of bleached fragments was largely similar to that of symbiotic fragments over all food treatments with few exceptions (Fig. 5 A, G, M, S). In P. lobata , symbiotic corals had significantly higher volume growth and respiration rates than bleached corals in most food treatments (Fig. 5 H, T). Differences in calcification and surface growth rates were smaller, but also significantly different for some food treatments (Fig. 5 B, N). In S. pistillata , differences in growth between symbiotic and bleached fragments were approx. twice as large as in the other species, with symbiotic corals growing significantly more than bleached fragments in all food treatments (Fig. 5 C, I, O). Although not significant, there is a trend indicating that the differences between symbiotic and bleached S. pistillata were greatest in the dissolved food treatment and decreased with increasing food complexity (Tab. S18-S21). Respiration rates were in a similar range across species and similar between symbiotic and bleached S. pistillata regardless of food treatment (Fig. 5 U). Discussion Growth differed between species regardless of symbiotic status Coral growth rates differed between species, with an approximately two- to three-fold higher calcification rate and ten-fold volume and tissue growth rates in Stylophora pistillata compared to Galaxea fascicularis and Porites lobata . These differences are in line with previously reported growth rates of the species (Dobson et al., 2021; Hii, Ambok Bolong, et al., 2009; Roik et al., 2016). Differences between bleached species were smaller, because of the larger decrease in growth in S. pistillata compared to the other species, indicating this species’ generally high reliance on autotrophic energy acquisition or concomitant decrease in heterotrophic uptake (Martinez et al., 2024). While symbiotic P. lobata had similar growth rates to G. fascicularis , bleached P. lobata grew more than bleached G. fascicularis . These shifts indicate a higher heterotrophic plasticity in P. lobata than in G. fascicularis , which is surprising given the large polyp size of G. fascicularis , which usually attributed high heterotrophic rates (Wijgerde et al., 2011) and its demonstrated high uptake of particulate food incl. Artemia nauplii (Hii et al., 2009). Food complexity has differential effects on growth of healthy corals All of the food components supplied to the corals in our feeding trials are generally considered beneficial to the growth of aquarium-raised marine organisms. For instance, microalgae including Tetraselmis chui , Chaetoceros gracilis , Isochrysis aff. galbana , and Dunaliella salina improved the growth of the juvenile clam Spondylus limbatus (Marquez et al., 2019) and they have previously been supplied to corals in successful ex-situ spawning approaches (Craggs et al., 2017). Yeast improved the growth of the juvenile Pacific white shrimp Litopenaeus vannamei (Zheng et al., 2021), amino acid enrichment of Artemia provided as a food improved the growth of the shrimp larvae of Litopenaeus vannamei (Nafisi Bahabadi et al., 2018). Artemia nauplii improved the growth and survival of juvenile and adult corals of the species Pocillopora acuta (Huang et al., 2020), Pocillopora damicornis (Conlan et al., 2018), Acropora tenuis , Favia fragum (Petersen et al., 2008), and Duncanopsammia axifuga (Tagliafico et al., 2018). To our knowledge, no prior data on honey as a food source are available and this component was included based on a report on its positive effects in a hobby aquarist forum. Although coral exposure to isolated carbohydrates (DOC) has been shown to affect coral health negatively (Pogoreutz et al., 2017), the complex carbohydrate mixture of honey together with its antimicrobial properties (Carnwath et al., 2014) might underlie its positive effects on corals. In symbiotic S. pistillata , volume and surface growth significantly increased with food complexity, with the high complexity feed resulting in 1.5.to 2-fold increased growth rates. This indicates two things, firstly, that it can be assumed that the synergy resulting from the combination of all food components in the high complexity feed provides the diversity of nutrients needed to support faster growth than when they are provided independently. This is in line with the higher growth of Goniopora columna fed with a complex mixture of ingredients compared to corals fed only with yeast and microalgae (Ding et al., 2021). Secondly, it indicates that S. pistillata has the heterotrophic capacity to supplement its high growth rates even further when supplied with the right nutrients. Ferrier-Pagès et al., (2003) showed that even moderate levels of feeding can enhance both tissue and skeletal growth of this coral species. This contrasts with the largely low but stable growth rates in G. fascicularis and P. lobata across food treatments indicating that these species do not benefit from additional heterotrophic supplementation when healthy. Higher food complexity increases growth of all bleached corals In bleached S. pistillata , growth parameters in the high complexity feed were two- to three-fold increased compared to all other food types, and all bleached fragments in the thawed plankton treatment died. While no mortality was recorded in P. lobata , the pattern was largely similar to that of S. pistillata in volume and surface growth, but the medium complexity feed also performed better than the less complex feeds. A similar trend, although not significant, was observed for G. fascicularis . These results illustrate the importance of food composition for bleached corals generally. Regardless of their assumed heterotrophic capacity, all species benefited from the most complex food composition when bleached. This results adds to a large body of literature that shows the positive effects of heterotrophic supplementation of bleached corals (Grottoli et al., 2006; Hughes & Grottoli, 2013; Rodrigues & Grottoli, 2007), which is also being explored as an active intervention technique in the field (Grottoli et al., 2025). The focus of this study was on the differences induced by the composition of the feed, but other factors including the amount of food and the frequency and timing of feeding may affect outcomes. We deliberately chose to supply the food treatments on a daily basis, given that corals in the reef have access to food regularly or near continuously. Compared to the majority of studies on heat stress and bleaching that do not or rarely supply food during experiments (Grottoli et al., 2021), the corals in our treatments are assumed to be fed closer to the point of satiation, mimicking field conditions more closely. This has downstream implications for the interpretation of our results. Given that it could be assumed that even suboptimal food composition at high density may have an enhancing effect on coral physiology, the differences between food treatments might be more nuanced with less or less frequent food supply during our experiment. Photosynthesis and respiration are similar between food types Photosynthesis and respiration were stable throughout the experiment and within ranges previously reported for the species (Puntin et al., 2023; Vetter et al., 2024). While it has been reported that heterotrophic feeding and food availability enhance photosynthetic (Houlbrèque & Ferrier-Pagès, 2009; Hoogenboom et al., 2010) and respiration rates (Borell et al., 2008; Dobson et al., 2021; Ferrier-Pagès et al., 2010) compared to starved corals, our results add that differences in the type of coral feed, i.e. its nutritional value, does not affect these variables. Whether food composition may play a role in modulating photosynthesis under more limited heterotrophic supply remains to be investigated. Effect of food types on heterotrophic compensation Metabolic rates were consistently higher in symbiotic fragments than in their bleached clones across all species. A reduction in calcification is one of the responses to bleaching stress, allowing corals to recover while maintaining a metabolic balance (Cohen & Holcomb, 2009; Dobson et al., 2021; Grottoli et al., 2017; Schoepf et al., 2015). However, the difference between bleached and symbiotic fragments strongly differed by species, with a positive correlation between the strength of the difference and the baseline productivity of the species. In the least productive species G. fascicularis , differences were smallest and growth and respiration of bleached fragments were similar to that of symbiotic fragments with few exceptions. Heterotrophic feeding has previously been reported to benefit the growth of bleached corals (Towle et al., 2015; Tremblay et al., 2016) and given the overall low productivity of G. fascicularis and its high heterotrophic food intake, all food treatments may have sufficed to compensate for the lack in autotrophic energy. In the intermediately productive P. lobata symbiotic fragments had significantly higher growth and respiration rates than bleached corals and in the highly productive S. pistillata , differences in growth between symbiotic and bleached fragments were approx. twice as large as in the other species. This result agrees with the assumptions that S. pistillata assimilates less heterotrophic nutrients under bleaching stress (Ferrier-Pagès et al., 2010; Grottoli et al., 2017; Martinez et al., 2024; Tremblay et al., 2012), has a limited heterotrophic plasticity (Alamaru et al., 2009), and/or uses growth reduction as a strategy to maintain total energy reserves and biomass (Grottoli et al., 2017). However, because of the lack of a starved control in our design, we cannot unequivocally determine whether the differences between bleached and symbiotic fragments over species are distinct due to their inherent productivity, their heterotrophic capacity (their ability to assimilate nutrients heterotrophically), or their heterotrophic plasticity (their ability to switch flexibly between autotrophic and heterotrophic assimilation). The food treatments did not have a clear effect on the differences between bleached and symbiotic fragments. This was largely due to the similarity of their effects on bleached and symbiotic fragments, resulting in a relative null compensation between symbiotic states. However, the high complexity feed resulted in high physiological rates of bleached corals that were in range with the physiological rates of symbiotic corals supplied with low complexity feeds, further supporting the notion that high complexity feeds boost the physiology of bleached corals. In conclusion, while the benefit of heterotrophic nutrition on healthy corals varied between species, we showed that complex heterotrophic food sources benefit the physiology of all bleached corals, regardless of their baseline productivity or their heterotrophic capacity and plasticity. This highlights that incorporating diverse particulate and dissolved feed components into restoration, aquaculture, or field supplementation protocols could bolster coral resilience to the increasing frequency of mass-bleaching events. Declarations Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Funding This study was conducted as part of the Ocean2100 global change simulation project of the Colombian-German Center of Excellence in Marine Sciences (CEMarin) funded by the German Academic Exchange Service (DAAD). The work was made possible with the support of a scholarship from the German Academic Exchange Service (DAAD) to MAL. Author contributions MAL: Investigation, experiment, data collection, data analysis and writing. LH: experiment, data collection and data analysis. ME: experiment and data collection. MZ: Supervision, conceptualization, research materials, data analysis, writing, review and editing. Acknowledgements We would like to thank the members of the Marine Holobiomics Lab for their support throughout the project, particularly Dr. Patrick Shubert and Christina Anding for technical support and animal caretaking. Data Availability Data and R scripts used can be found online at: https://github.com/Antonieta20/Heterotrophy-on-bleached-corals References Agostini, S., Fujimura, H., Higuchi, T., Yuyama, I., Casareto, B. E., Suzuki, Y., & Nakano, Y. (2013). 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Effects of yeast and yeast extract on growth performance, antioxidant ability and intestinal microbiota of juvenile Pacific white shrimp ( Litopenaeus vannamei ). Aquaculture , 530 , 735941. https://doi.org/10.1016/j.aquaculture.2020.735941 Supplementary Files Lopezfoodcomplexitysupplement.docx Cite Share Download PDF Status: Published Journal Publication published 10 Mar, 2026 Read the published version in Marine Biology → Version 1 posted Editorial decision: Revise and Resubmit 25 Aug, 2025 Reviewers agreed at journal 12 Jul, 2025 Reviewers invited by journal 08 Jul, 2025 Editor assigned by journal 30 May, 2025 First submitted to journal 28 May, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-6767958","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":482629912,"identity":"4df2341d-a8be-4cf2-bb92-5917c8435a98","order_by":0,"name":"María Antonieta López","email":"","orcid":"","institution":"Justus-Liebig-Universität Gießen: Justus-Liebig-Universitat Giessen","correspondingAuthor":false,"prefix":"","firstName":"María","middleName":"Antonieta","lastName":"López","suffix":""},{"id":482629913,"identity":"3473961d-249c-4530-9f55-8078a1d39647","order_by":1,"name":"Lea Hiemer","email":"","orcid":"","institution":"Justus-Liebig-Universität Gießen: Justus-Liebig-Universitat Giessen","correspondingAuthor":false,"prefix":"","firstName":"Lea","middleName":"","lastName":"Hiemer","suffix":""},{"id":482629914,"identity":"d7a8e9e5-42df-4c8f-a376-388251ae2e89","order_by":2,"name":"Marie Engel","email":"","orcid":"","institution":"Justus-Liebig-Universität Gießen: Justus-Liebig-Universitat Giessen","correspondingAuthor":false,"prefix":"","firstName":"Marie","middleName":"","lastName":"Engel","suffix":""},{"id":482629915,"identity":"b2e739a5-478d-42d2-a164-5763b9c103d8","order_by":3,"name":"Maren Ziegler","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0003-2237-9261","institution":"Justus Liebig University Giessen: Justus-Liebig-Universitat Giessen","correspondingAuthor":true,"prefix":"","firstName":"Maren","middleName":"","lastName":"Ziegler","suffix":""}],"badges":[],"createdAt":"2025-05-28 12:09:17","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6767958/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6767958/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s00227-026-04806-9","type":"published","date":"2026-03-10T15:59:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86452584,"identity":"bce89864-d1cd-48a9-8450-dc3486c0aced","added_by":"auto","created_at":"2025-07-10 20:07:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":466746,"visible":true,"origin":"","legend":"\u003cp\u003eConceptual experimental overview. \u003cem\u003eGalaxea fascicularis, Porites lobata, \u003c/em\u003eand \u003cem\u003eStylophora pistillata \u003c/em\u003esymbiotic and bleached, exposed to five food options combining dissolved and particulate food types:tplankton; \u003cem\u003eArtemia salina\u003c/em\u003e nauplii; three microalgae species; honey; yeast, and amino acids. Coral growth and respiration of symbiotic and bleached corals were measured at the beginning (T0) and at the end of the 18 weeks (T2), photosynthesis and respiration rates of symbiotic corals were measured at T0, after three weeks of feeding (T1), and at T2.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/95166b90e9056c644de0a646.png"},{"id":86452585,"identity":"78274f64-36ee-4757-8d6f-23292e5fc2d9","added_by":"auto","created_at":"2025-07-10 20:07:45","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":354060,"visible":true,"origin":"","legend":"\u003cp\u003eGrowth rates and respiration of the symbiotic and bleached stony corals \u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata,\u003c/em\u003e and \u003cem\u003eStylophora pistillata\u003c/em\u003e fed over 18 weeks. The differences between species in calcification (A), volume growth (B) and surface area growth (C) and respiration rate (D) are shown. Significance codes are defined as: \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.001 (***), \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01 (**).\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/01fd5fffd54857ab6ec377a5.png"},{"id":86452596,"identity":"a37ac181-e3ff-452b-931a-ba5c60ec55b9","added_by":"auto","created_at":"2025-07-10 20:07:46","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":777198,"visible":true,"origin":"","legend":"\u003cp\u003eGrowth and photosynthesis rates of the symbiotic stony corals \u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata,\u003c/em\u003e and \u003cem\u003eStylophora pistillata\u003c/em\u003e fed with different food treatments over 18 weeks. The differences between food options in calcification growth (A-C), volume growth (D-F), surface area growth (G-I), respiration (J-L), net photosynthesis (M-O), and gross photosynthesis (P-R) are shown as boxplots. Groups with different letters are significantly different based on linear mixed-effects models (p \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/b96eee130a9445b4f5c49851.png"},{"id":86452586,"identity":"61d8337d-a554-48ba-b9a7-a85ee828e198","added_by":"auto","created_at":"2025-07-10 20:07:45","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":877034,"visible":true,"origin":"","legend":"\u003cp\u003eGrowth and respiration of the menthol-bleached stony corals \u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata,\u003c/em\u003e and \u003cem\u003eStylophora pistillata\u003c/em\u003e fed with different food treatments over 18 weeks. The differences between food treatments in calcification (A-C), volume growth (D-F), surface area growth (G-I), and respiration rates (J-L) are shown as boxplots. Groups with different letters are significantly different based on linear mixed-effects models (\u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05).\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/1fd47836db3c677f5f84ed70.png"},{"id":86453107,"identity":"bf9dd339-b09e-4eaf-98f5-efed99568c69","added_by":"auto","created_at":"2025-07-10 20:15:45","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1513186,"visible":true,"origin":"","legend":"\u003cp\u003eGrowth rates and respiration of the symbiotic and bleached stony corals \u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata,\u003c/em\u003e and \u003cem\u003eStylophora pistillata\u003c/em\u003e fed with five food treatments over 18 weeks. The differences between symbiotic and bleached corals in calcification (A-C), volume growth (G-I), surface area growth (M-O), and respiration rates (S-U) are shown as boxplots, and the magnitude of these differences between symbiotic and bleached fragments in calcification (D-F), volume growth (J-L), surface area growth (P-R), and respiration rates (V-X) are shown as Hedges’ g effect sizes. Bleached \u003cem\u003eS. pistillata\u003c/em\u003e fragments fed with thawed plankton died during the experiment. Significance codes used are defined as: \u003cem\u003ep\u003c/em\u003e\u0026lt; 0.001 (***), \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.01 (**), \u003cem\u003ep\u003c/em\u003e \u0026lt; 0.05 (*).\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/d553367869f892d0855d021d.png"},{"id":104740287,"identity":"3842351d-af77-4875-af1b-41e23ff254ac","added_by":"auto","created_at":"2026-03-16 16:16:26","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4978482,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/0adcabe8-a8fc-4342-aa9b-3029fd54626b.pdf"},{"id":86453106,"identity":"a6b05156-6c08-47a1-9ed6-316112d185b7","added_by":"auto","created_at":"2025-07-10 20:15:45","extension":"docx","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":695716,"visible":true,"origin":"","legend":"","description":"","filename":"Lopezfoodcomplexitysupplement.docx","url":"https://assets-eu.researchsquare.com/files/rs-6767958/v1/cf992075a421141c696327cb.docx"}],"financialInterests":"","formattedTitle":"Complex food sources aid physiological compensation of bleached corals","fulltext":[{"header":"Introduction","content":"\u003cp\u003eCoral reefs are highly productive ecosystems that provide an essential basis for marine biodiversity (Moberg \u0026amp; Folke, 1999), supporting up to a third of all marine animal and plant species, despite energy 100%covering only about 0.15% of the ocean surface (Roberts et al., 2002). As a result of prolonged and more severe marine heatwaves, recurrent coral bleaching events are threatening coral reefs around the world (Eakin et al., 2022; T. P. Hughes et al., 2018). Coral bleaching refers to the loss of the symbiotic unicellular dinoflagellate microalgae of the Symbiodiniaceae family from coral tissue, where they provide most of their energetic needs through photosynthesis (Gates et al., 1992; Muscatine \u0026amp; Cernichiari, 1969). The loss of the Symbiodiniaceae disrupts the main energy acquisition pathway for the corals which alters physiology from growth to reproduction, leads to tissue loss, and ultimately the death of the host (Agostini et al., 2013; Baird \u0026amp; Marshall, 2002; Hoegh-Guldberg et al., 2007).\u003c/p\u003e\u003cp\u003eIn addition to autotrophic energy acquisition through their symbiosis with microalgae, scleractinian corals complement their energetic needs through heterotrophic feeding (Lewis \u0026amp; Price, 1975). The expansion and movement of their polyps and tentacles allows them to swirl the water, filter out or catch prey, and digest it (Price \u0026amp; Patterson, 2023). Under normal conditions, it is assumed that heterotrophy supplies stony corals with vital nutrients that cannot be sufficiently provided via their photoautotrophic symbionts, such as phosphate and nitrogen (Houlbr\u0026egrave;que \u0026amp; Ferrier-Pag\u0026egrave;s, 2009; Muscatine et al., 1984). Heterotrophic supplementation has positive effects primarily on the calcification rate, tissue growth, respiration as well as on chlorophyll density and photosynthetic rate (Houlbr\u0026egrave;que \u0026amp; Ferrier-Pag\u0026egrave;s, 2009; Pr\u0026eacute;zelin, 1987; Swanson \u0026amp; Hoegh-Guldberg, 1998). During coral bleaching, the capacity to meet the nutritional requirements through heterotrophic feeding becomes essential for survival (Houlbr\u0026egrave;que \u0026amp; Ferrier-Pag\u0026egrave;s, 2009; Hughes \u0026amp; Grottoli, 2013). Corals with higher heterotrophic plasticity are able to maintain higher energy reserves (Grottoli et al., 2006; Rodrigues \u0026amp; Grottoli, 2007) and are more resistant to and recover faster from heat stress (Borell et al., 2008; Connolly et al., 2012; Grottoli et al., 2006).\u003c/p\u003e\u003cp\u003eHeterotrophic plasticity, i.e. the flexibility in how and how much an organism relies on consuming organic matter rather than on autotrophy to survive and grow, varies among coral species and colonies of the same species (Grottoli et al., 2006; Hoogenboom et al., 2010). While some coral species maintain a fixed feeding strategy regardless of environmental fluctuations, limiting their stress tolerance, others exhibit higher trophic plasticity, shifting their feeding mode along the autotrophy-heterotrophy spectrum (Sturaro et al., 2021). The ability to switch between autotrophic and heterotrophic feeding in response to environmental conditions may explain why some coral species are more resilient to changing variables (e.g., increasing depth, turbidity) or stressors (e.g., heat) (Anthony \u0026amp; Fabricius, 2000; Grottoli et al., 2006; Swain et al., 2016).\u003c/p\u003e\u003cp\u003eNot only heterotrophic plasticity, but also the specific type of food, may be critical for maintaining energy reserves and supporting key physiological functions such as growth and reproduction of healthy corals. For example, Craggs et al. (2017) successfully induced spawning in four \u003cem\u003eAcropora\u003c/em\u003e species for the first time in a closed mesocosm system using a complex diet that included amino acids, picoplankton, nanoplankton, microplankton, mesoplankton, baker\u0026rsquo;s yeast, and microalgae. Similarly, Osinga et al. (2011) demonstrated that feeding with \u003cem\u003eArtemia\u003c/em\u003e significantly enhanced the growth of \u003cem\u003eSeriatopora caliendrum\u003c/em\u003e and Zaidi et al. (2023) reported that \u003cem\u003eAcropora digitifera\u003c/em\u003e corals fed with \u003cem\u003eArtemia\u003c/em\u003e and Budu (a fermented anchovy extract) exhibited higher growth and survival rates compared to unfed controls. However, the potential of different food types to compensate for productivity loss in bleached corals has never been investigated systematically. Therefore, the main goal of this study was to investigate the influence of heterotrophic nutrition on the physiology of scleractinian corals and evaluate the potential of different food types to compensate for productivity losses in bleached vs. symbiotic corals. The specific goals were to investigate the effects of different food types on: i) the physiology of symbiotic corals, ii) the physiology of bleached corals, and iii) the physiological compensation comparing symbiotic and bleached corals.\u003c/p\u003e\u003cp\u003eTo this end, we conducted a 21-week aquarium experiment, providing five food treatments of varying complexity composed of dissolved and particulate feeds to symbiotic and bleached fragments of the coral species \u003cem\u003eGalaxea fascicularis\u003c/em\u003e (Linnaeus 1767), \u003cem\u003ePorites lobata\u003c/em\u003e (Dana 1846), and \u003cem\u003eStylophora pistillata\u003c/em\u003e (Esper, 1792). We measured coral growth, photosynthesis, and respiration as proxies for physiological compensation. As the frequency and severity of bleaching events increases and the loss of coral cover is dramatic in all reef areas around the world, understanding the mechanisms that affect heterotrophic plasticity could shed light on acclimatization mechanisms and supplementation strategies that can contribute to survival of bleached corals.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003eExperimental design\u003c/h2\u003e\u003cp\u003eThe experiment was designed to investigate the influence of heterotrophic nutrition on the physiology of the three scleractinian coral species \u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata\u003c/em\u003e and \u003cem\u003eStylophora pistillata\u003c/em\u003e in their symbiotic and bleached conditions. The experiment consisted of five treatments combining dissolved and particulate food types: thawed red plankton, freshly-hatched \u003cem\u003eArtemia salina\u003c/em\u003e nauplii, three microalgae species, honey, yeast, and amino acids that were used to feed the corals over a 18-week period. (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eEach of the five treatments was triplicated with a total of 15 \u0026times; 40-L tanks. The tanks were part of a 3,000-L water recirculation system, and each experimental tank had a separate water inlet and outlet with a water exchange of 20 L h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The equipment per tank consisted of a wavemaker pump (easyStream pro ES-28, Aqualight GmbH, Bramsche/Lappenstuhl, Germany), a titanium heater to maintain the temperature between 26 and 27\u0026deg;C (Schego Heater 300 W, Schemel \u0026amp; Goetz GmbH, Germany), and four LED light strips with photosynthetically active radiation (PAR) between 140 and 190 \u0026micro;mol photons m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e a light-dark cycle of 10:14 hours. The coral fragments were suspended on three plastic rods in each tank (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e).\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003eCoral species and replication\u003c/h3\u003e\n\u003cp\u003eFor the experiment, three coral colonies of each of the species \u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata\u003c/em\u003e, and \u003cem\u003eStylophora pistillata\u003c/em\u003e were sourced from the \u003cem\u003eOcean2100\u003c/em\u003e coral aquarium facility of the Justus Liebig University Giessen, Germany (Tab. S1). The colonies were fragmented (3\u0026ndash;8 cm length) using a hammer and chisel, and allowed to heal for eight weeks before starting the experiment. Thirty fragments per colony, 90 fragments per species (of which half were bleached), and 270 fragments in total were used. The fragments were evenly distributed in the tanks and treatments, resulting in 18 fragments, six per species with two fragments per colony (one symbiotic and one bleached), per tank.\u003c/p\u003e\n\u003ch3\u003eMenthol bleaching\u003c/h3\u003e\n\u003cp\u003eAfter eight weeks of acclimation, the coral fragments were randomly divided into two groups, which contained half of the coral fragments per genotype (15 fragments per genotype, 45 fragments per group per species). To chemically bleach the corals, we followed the protocols modified by Wang et al. (2012) and Bauer et al. (in preparation). Briefly, the bleaching consists of three days of treatment with 0.38 mM menthol in filtered (65 \u0026micro;m) seawater, followed by one day of rest and another day of menthol treatment. Menthol incubations lasted 8 h during the light period (Puntin, Wong, et al., 2023). Menthol bleaching was repeated for two days when corals started to regain color during the experiment. \u003cem\u003eS. pistillata\u003c/em\u003e was rebleached once after 9 weeks, \u003cem\u003eG. fascicularis\u003c/em\u003e was rebleached twice after 9 and 13 weeks, and \u003cem\u003eP. lobata\u003c/em\u003e was rebleached five times after 6, 9, 12, 14, and 16 weeks.\u003c/p\u003e\n\u003ch3\u003eFeeding\u003c/h3\u003e\n\u003cp\u003eCoral fragments were fed with one of five food options combining dissolved and particulate food types: red plankton, \u003cem\u003eArtemia salina\u003c/em\u003e nauplii, three microalgae species, honey, yeast, and an amino acid mixture (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The choice of these types of food was based on their nutritional value i.e., sources of carbon and nitrogen, and their beneficial effects on coral physiology, i.e., increased growth, up-regulation of photosynthesis (Craggs et al., 2017; Ferrier, 1991; Houlbr\u0026egrave;que \u0026amp; Ferrier-Pag\u0026egrave;s, 2009; Osinga et al., 2011; Zaidi et al., 2023).\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eInformation on the components and concentrations of the food treatments supplied to three stony coral species every day for three hours over an 18-week period.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"6\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eFood components\u003c/p\u003e\u003cp\u003e[Concentration]\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eThawed plankton\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eDissolved food\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eLow complexity\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eMedium complexity\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eHigh complexity\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eAmino acids\u003c/p\u003e\u003cp\u003e[0.025 \u0026micro;l ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eDry yeast\u003c/p\u003e\u003cp\u003e[3,200 cells ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eHoney\u003c/p\u003e\u003cp\u003e[20 \u0026micro;g ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eMicroalgae: \u003cem\u003eTisochrysis lutea\u003c/em\u003e, \u003cem\u003eChaetoceros calcitrans, Tetraselmis chui\u003c/em\u003e\u003c/p\u003e\u003cp\u003e[5,000 cells ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e per species]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cem\u003eArtemia salina\u003c/em\u003e nauplii\u003c/p\u003e\u003cp\u003e[0.4 \u0026micro;g wet weight ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eThawed plankton\u003c/p\u003e\u003cp\u003e[0.4 \u0026micro;g wet weight ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e]\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e✓\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u0026nbsp;\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u0026nbsp;\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe following concentrations were applied for each composite of the food types: 0.025 \u0026micro;l ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e of amino acid mixture (Pohl's Xtra special, Korallenzucht.de Vertriebs GmbH, Germany) was used. Amino acids dissolved in water are a natural source of nitrogen for stony corals (Ferrier, 1991). 0.03 g of dry baker's yeast (REWE supermarket, Germany) was used resulting in 3,200 cells ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. For each feeding tank, the dry yeast was weighed on a precision balance (Kern KB 360-3N, KERN \u0026amp; Sohn GmbH, Germany, precision: 0.001 g). and dissolved with water from the aquarium system. Dry yeast is a source of carbon and nitrogen, proteins, B-vitamins, pigments and complex carbohydrates, such as glucans and has been used in experiments with stony corals as a supplementary diet (Craggs et al., 2017). Organic honey (REWE supermarket, Germany) was supplied at 20 \u0026micro;g ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. The honey was weighed and mixed with water from the facility before addition to the tanks. The usage of honey as a feeding option for corals to bolster their health has been explored among coral hobbyists and aquarists (Sebastian, 2017). One gram of honey contains about 0.32 g of carbon. Three species of microalgae were used: \u003cem\u003eTetraselmis chui\u003c/em\u003e (Chlorophyte, 10 to 25 \u0026micro;m diameter, Montoya et al., 2024), \u003cem\u003eChaetoceros calcitrans\u003c/em\u003e (Diatom, 5 to 10 \u0026micro;m, De La Pe\u0026ntilde;a et al., 2018), and \u003cem\u003eTisochrysis lutea\u003c/em\u003e (Haptophyte, 3 to 7.5 \u0026micro;m, Heimann \u0026amp; Huerlimann, 2015) at a concentration of 5000 cells ml\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (5 x 10\u003csup\u003e6\u003c/sup\u003e cells L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) each. \u003cem\u003eT. lutea\u003c/em\u003e was grown in 0.1% sterile-filtered (0.22 \u0026micro;m) Walne's medium (aquacare-shop, Germany), while \u003cem\u003eT. chui\u003c/em\u003e and \u003cem\u003eC. calcitrans\u003c/em\u003e were grown in sterile-filtered Guillard's F/2 medium with 0.1% silicate added to the medium for \u003cem\u003eC. calcitrans.\u003c/em\u003e Microalgal cultures were maintained at 20\u0026ndash;21\u0026deg;C, 47 \u0026micro;mol photon m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e \u0026micro;mol, and a light cycle of 12 hours. The cell count was determined daily from the cultures using a Thoma hemocytometer. The corresponding volumes of the microalgae cultures were then centrifuged twice at 3,000 g for 10 min and resuspended in 50 ml seawater to wash out the medium. Depending on the algae species, the nutritional composition of lipids and carbohydrates may vary, but all have high levels of protein and essential fatty acids, as well as being good sources of ascorbic acid and riboflavin (Brown et al., 1997). Additionally, microalgae are a source of carbon for corals, which is used by both symbiotic and aposymbiotic corals (Leal et al., 2014). 0.8 g of wet mass of freshly hatched \u003cem\u003eArtemia salina\u003c/em\u003e nauplii (prepared 24 hours before the feeding, 400\u0026ndash;500 \u0026micro;m length) was used, which corresponds to approximately 22,000 nauplii L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. \u003cem\u003eArtemia salina\u003c/em\u003e nauplii are a source of nitrogen, carbon, carbohydrates, lipids and proteins and they are frequently used by aquarists and researchers to feed corals (Zaidi et al., 2023). 0.8 g of thawed red plankton (1000\u0026ndash;2000 \u0026micro;m length) (Calanoide Copepoden, Zooschatz, Germany), resulting in approximately 1,000 organisms L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Frozen food was thawed, thoroughly rinsed in a sieve, and mixed with seawater from the aquarium system before addition to a feeding tank. The red plankton consists mainly of marine copepods, micronized shrimp larvae, seawater rotifers and salmon oil, and is a second standard feed in coral aquaculture.\u003c/p\u003e\u003cp\u003eEach feeding tank was filled with 20 L of seawater, which was taken from the experimental aquarium system and roughly filtered (65 \u0026micro;m filter). Additionally, each tank was equipped with a pump for water circulation and a heater to maintain the temperature between 26 and 27\u0026deg;C. Feeding lasted three hours around dusk, i.e., it started 1.5 hours before the lights were turned off and took place at a light intensity about 10 \u0026micro;mol photons m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to a twilight phase.\u003c/p\u003e\n\u003ch3\u003ePhysiological measurements\u003c/h3\u003e\n\u003cp\u003eTo assess the effects of the different food types on the coral holobiont and photosymbiont physiology, we measured coral growth, photosynthesis and respiration rates after three weeks of feeding and after 18 weeks of feeding.\u003c/p\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003eCoral growth\u003c/h2\u003e\u003cp\u003eAs proxies of coral growth, changes in calcification, volume growth, and surface area growth were used as a holobiont response to the food options. Calcification was measured following the buoyant-weighing method (Davies, 1989). Briefly, an 8-L aquarium was filled up with seawater from the experimental system. Corals were weighed with a precision balance using an under-floor weighing hook of the balance (Kern KB 360-3N, KERN \u0026amp; Sohn GmbH, Germany, precision: 0.001 g). The temperature of the water was kept constant at 26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u0026deg;C with a submersible heater and salinity at 35. Volume growth and surface area of each fragment were measured using 3D scanning. For this, a handheld 3D scanner (Artec Spider 3D, Artec 3D, Luxembourg) was used together with the scanning software Artec Studio 16 (Artec 3D, Luxembourg) following Reichert et al. (2016). Coral fragments were placed on an automatic turning table, positioned in a 80 x 80 x 80 cm sized macrophoto studio and scanned within 40\u0026ndash;50 s from two angles in two full rotations. Scans of the corals resulted in image point clouds, from which polygon structures were constructed. Finally, models built for each fragment were exported as .obj files. Surface area and volume were calculated in MeshLab Visual Computing Lab-ISTI-CNR (v.1.3.4 Β, 2014) using the \u0026lsquo;compute geometric measures\u0026rsquo; tool. Finally, growth rates were calculated as the difference between the measurements taken before the start of the feeding regimes and after 18 weeks of feeding at the end of the experiment. Calcification rate and volume growth were standardized to surface area.\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003ePhotosynthesis and respiration rates\u003c/h3\u003e\n\u003cp\u003eNet photosynthesis, respiration, and gross photosynthesis of symbiotic corals and respiration of bleached corals were measured as change in oxygen concentrations during incubations in light and dark. Specifically, the corals were placed in airtight sealed 1-L incubation jars that were filled with seawater from the experimental system. Oxygen concentration was measured at the beginning and at the end of the 60-min incubation with an optical oxygen sensor connected to a hand-held multi-parameter probe (Multi 3620 IDS SET G, Xylem Analytics, Germany). Each incubation run included two control jars without corals to correct for biological activity in the seawater. Net photosynthesis and respiration were corrected with the change in oxygen in the controls and normalized to incubation volume, incubation time, and coral surface area. Gross photosynthesis was calculated as the sum of net photosynthesis and respiration.\u003c/p\u003e\n\u003ch3\u003eStatistical analyses\u003c/h3\u003e\n\u003cp\u003eStatistical analyses were conducted in R (R version 4.2.2, (R Core Team, 2022) using the graphical user interface \u0026lsquo;RStudio\u0026rsquo; (Version 2022.12.0\u0026thinsp;+\u0026thinsp;353, RStudio Inc., USA). To obtain coral growth, we converted the values from buoyant weight to actual weight using the seacarb package (Gattuso et al., 2021). To test the effects of different food types on the physiology of symbiotic and bleached corals, we used linear mixed-effects models with treatment (five levels: thawed plankton, dissolved food, low complexity, medium complexity, high complexity) as fixed factor and coral colony as random factor. Individual models were constructed for each response variable and species. The models were fitted using the lme4 package (Bates et al., 2015) and residual distributions were tested for normality and heteroscedasticity. If necessary, data were log-transformed to meet test assumptions. Models were analyzed using a post hoc test from the \u0026lsquo;multcomp\u0026rsquo; package (Hothorn et al. 2020) with Tukey comparison with \u0026lsquo;holm\u0026rsquo; adjustment for multiple testing. Model specifications can be found in supplemental material (Tabs. S2-15). To test the magnitude of the differences between symbiotic and bleached corals between the different food types, we calculated Hedges\u0026rsquo; g effect sizes within each feeding regime on raw data for each variable. Finally, all results were visualized using \u0026lsquo;ggplot2\u0026rsquo; (Wickham, 2016).\u003c/p\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003eCoral growth rates\u003c/h2\u003e\u003cp\u003eCoral growth rates differed between species, with an approximately two- to three-fold higher calcification rate and ten-fold volume and tissue growth rates in symbiotic \u003cem\u003eStylophora pistillata\u003c/em\u003e compared to symbiotic \u003cem\u003eGalaxea fascicularis\u003c/em\u003e and \u003cem\u003ePorites lobata\u003c/em\u003e, which had similar growth rates to each other (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA-C; Tab. S2). Respiration rates of symbiotic \u003cem\u003eP. lobata\u003c/em\u003e were significantly higher than of \u003cem\u003eG. fascicularisi\u003c/em\u003e, and \u003cem\u003eS. pistillata\u003c/em\u003e had intermediate respiration rates (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD). Growth was reduced in all bleached corals and \u003cem\u003eS. pistillata\u003c/em\u003e still maintained significantly higher growth rates than \u003cem\u003eG. fascicularis\u003c/em\u003e and \u003cem\u003eP. lobata\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Bleached \u003cem\u003eP. lobata\u003c/em\u003e had intermediate growth rates that were significantly higher than in bleached \u003cem\u003eG. fascicularis\u003c/em\u003e. Respiration rates were similar between all species when bleached (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eD).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e\u003ch2\u003eEffects of food types on the physiology of symbiotic corals\u003c/h2\u003e\u003cp\u003eIn symbiotic corals, growth was not affected by the different food types in \u003cem\u003eG. fascicularis\u003c/em\u003e and \u003cem\u003eP. lobata\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Tab. S3, S5). In \u003cem\u003eS. pistillata\u003c/em\u003e, volume and surface growth significantly increased with food complexity, with the high complexity feed resulting in highest growth rates (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF, I, Tab. S7). Respiration rates of all species were comparable (range 10\u0026ndash;30 \u0026micro;g O\u003csub\u003e2\u003c/sub\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and largely unaffected by food types (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, Tab. S4, S6, S8). Similar to coral growth, photosynthetic rates in \u003cem\u003eS. pistillata\u003c/em\u003e were approximately double that of \u003cem\u003eG. fascicularis\u003c/em\u003e and \u003cem\u003eP. lobata\u003c/em\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section2\"\u003e\u003ch2\u003eEffects of food types on the physiology of bleached corals\u003c/h2\u003e\u003cp\u003eCalcification rate and volume and tissue growth rates in bleached \u003cem\u003eS. pistillata\u003c/em\u003e were all approximately two-fold higher compared to \u003cem\u003eG. fascicularis\u003c/em\u003e and \u003cem\u003eP. lobata\u003c/em\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e; Tab. S2). In \u003cem\u003eS. pistillata\u003c/em\u003e, growth parameters in the high complexity feed were two- to three-fold increased compared to all other food types, and all bleached fragments in the thawed plankton treatment died (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Tab. S11). While no mortality was recorded in \u003cem\u003eP. lobata\u003c/em\u003e, the pattern was largely similar to that of \u003cem\u003eS. pistillata in\u003c/em\u003e volume and surface growth, but the medium complexity feed also performed better than the less complex feeds (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). A similar trend, although not significant, was observed for \u003cem\u003eG. fascicularis\u003c/em\u003e. Respiration rates of all bleached species were comparable (range 5\u0026ndash;20 \u0026micro;g O\u003csub\u003e2\u003c/sub\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and largely unaffected by food types (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Tab. S12).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\u003ch2\u003eEffect of food types on heterotrophic compensation\u003c/h2\u003e\u003cp\u003eMetabolic rates were consistently higher in symbiotic fragments than in their bleached clones across all species (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). The food treatments did not have a clear effect on the differences between bleached and symbiotic fragments in any of the species. Differences were smallest in \u003cem\u003eG. fascicularis\u003c/em\u003e, in which the growth and respiration of bleached fragments was largely similar to that of symbiotic fragments over all food treatments with few exceptions (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA, G, M, S). In \u003cem\u003eP. lobata\u003c/em\u003e, symbiotic corals had significantly higher volume growth and respiration rates than bleached corals in most food treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eH, T). Differences in calcification and surface growth rates were smaller, but also significantly different for some food treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB, N). In \u003cem\u003eS. pistillata\u003c/em\u003e, differences in growth between symbiotic and bleached fragments were approx. twice as large as in the other species, with symbiotic corals growing significantly more than bleached fragments in all food treatments (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC, I, O). Although not significant, there is a trend indicating that the differences between symbiotic and bleached \u003cem\u003eS. pistillata\u003c/em\u003e were greatest in the dissolved food treatment and decreased with increasing food complexity (Tab. S18-S21). Respiration rates were in a similar range across species and similar between symbiotic and bleached \u003cem\u003eS. pistillata\u003c/em\u003e regardless of food treatment (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eU).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"Discussion","content":"\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003eGrowth differed between species regardless of symbiotic status\u003c/h2\u003e\u003cp\u003eCoral growth rates differed between species, with an approximately two- to three-fold higher calcification rate and ten-fold volume and tissue growth rates in \u003cem\u003eStylophora pistillata\u003c/em\u003e compared to \u003cem\u003eGalaxea fascicularis\u003c/em\u003e and \u003cem\u003ePorites lobata\u003c/em\u003e. These differences are in line with previously reported growth rates of the species (Dobson et al., 2021; Hii, Ambok Bolong, et al., 2009; Roik et al., 2016). Differences between bleached species were smaller, because of the larger decrease in growth in \u003cem\u003eS. pistillata\u003c/em\u003e compared to the other species, indicating this species\u0026rsquo; generally high reliance on autotrophic energy acquisition or concomitant decrease in heterotrophic uptake (Martinez et al., 2024). While symbiotic \u003cem\u003eP. lobata\u003c/em\u003e had similar growth rates to \u003cem\u003eG. fascicularis\u003c/em\u003e, bleached \u003cem\u003eP. lobata\u003c/em\u003e grew more than bleached \u003cem\u003eG. fascicularis\u003c/em\u003e. These shifts indicate a higher heterotrophic plasticity in \u003cem\u003eP. lobata\u003c/em\u003e than in \u003cem\u003eG. fascicularis\u003c/em\u003e, which is surprising given the large polyp size of \u003cem\u003eG. fascicularis\u003c/em\u003e, which usually attributed high heterotrophic rates (Wijgerde et al., 2011) and its demonstrated high uptake of particulate food incl. \u003cem\u003eArtemia\u003c/em\u003e nauplii (Hii et al., 2009).\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e\u003ch2\u003eFood complexity has differential effects on growth of healthy corals\u003c/h2\u003e\u003cp\u003eAll of the food components supplied to the corals in our feeding trials are generally considered beneficial to the growth of aquarium-raised marine organisms. For instance, microalgae including \u003cem\u003eTetraselmis chui\u003c/em\u003e, \u003cem\u003eChaetoceros gracilis\u003c/em\u003e, \u003cem\u003eIsochrysis aff. galbana\u003c/em\u003e, and \u003cem\u003eDunaliella salina\u003c/em\u003e improved the growth of the juvenile clam \u003cem\u003eSpondylus limbatus\u003c/em\u003e (Marquez et al., 2019) and they have previously been supplied to corals in successful ex-situ spawning approaches (Craggs et al., 2017). Yeast improved the growth of the juvenile Pacific white shrimp \u003cem\u003eLitopenaeus vannamei\u003c/em\u003e (Zheng et al., 2021), amino acid enrichment of \u003cem\u003eArtemia\u003c/em\u003e provided as a food improved the growth of the shrimp larvae of \u003cem\u003eLitopenaeus vannamei\u003c/em\u003e (Nafisi Bahabadi et al., 2018). \u003cem\u003eArtemia\u003c/em\u003e nauplii improved the growth and survival of juvenile and adult corals of the species \u003cem\u003ePocillopora acuta\u003c/em\u003e (Huang et al., 2020), \u003cem\u003ePocillopora damicornis\u003c/em\u003e (Conlan et al., 2018), \u003cem\u003eAcropora tenuis\u003c/em\u003e, \u003cem\u003eFavia fragum\u003c/em\u003e (Petersen et al., 2008), and \u003cem\u003eDuncanopsammia axifuga\u003c/em\u003e (Tagliafico et al., 2018). To our knowledge, no prior data on honey as a food source are available and this component was included based on a report on its positive effects in a hobby aquarist forum. Although coral exposure to isolated carbohydrates (DOC) has been shown to affect coral health negatively (Pogoreutz et al., 2017), the complex carbohydrate mixture of honey together with its antimicrobial properties (Carnwath et al., 2014) might underlie its positive effects on corals.\u003c/p\u003e\u003cp\u003eIn symbiotic \u003cem\u003eS. pistillata\u003c/em\u003e, volume and surface growth significantly increased with food complexity, with the high complexity feed resulting in 1.5.to 2-fold increased growth rates. This indicates two things, firstly, that it can be assumed that the synergy resulting from the combination of all food components in the high complexity feed provides the diversity of nutrients needed to support faster growth than when they are provided independently. This is in line with the higher growth of \u003cem\u003eGoniopora columna\u003c/em\u003e fed with a complex mixture of ingredients compared to corals fed only with yeast and microalgae (Ding et al., 2021). Secondly, it indicates that \u003cem\u003eS. pistillata\u003c/em\u003e has the heterotrophic capacity to supplement its high growth rates even further when supplied with the right nutrients. Ferrier-Pag\u0026egrave;s et al., (2003) showed that even moderate levels of feeding can enhance both tissue and skeletal growth of this coral species. This contrasts with the largely low but stable growth rates in \u003cem\u003eG. fascicularis\u003c/em\u003e and \u003cem\u003eP. lobata\u003c/em\u003e across food treatments indicating that these species do not benefit from additional heterotrophic supplementation when healthy.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section2\"\u003e\u003ch2\u003eHigher food complexity increases growth of all bleached corals\u003c/h2\u003e\u003cp\u003eIn bleached \u003cem\u003eS. pistillata\u003c/em\u003e, growth parameters in the high complexity feed were two- to three-fold increased compared to all other food types, and all bleached fragments in the thawed plankton treatment died. While no mortality was recorded in \u003cem\u003eP. lobata\u003c/em\u003e, the pattern was largely similar to that of \u003cem\u003eS. pistillata in\u003c/em\u003e volume and surface growth, but the medium complexity feed also performed better than the less complex feeds. A similar trend, although not significant, was observed for \u003cem\u003eG. fascicularis\u003c/em\u003e. These results illustrate the importance of food composition for bleached corals generally. Regardless of their assumed heterotrophic capacity, all species benefited from the most complex food composition when bleached. This results adds to a large body of literature that shows the positive effects of heterotrophic supplementation of bleached corals (Grottoli et al., 2006; Hughes \u0026amp; Grottoli, 2013; Rodrigues \u0026amp; Grottoli, 2007), which is also being explored as an active intervention technique in the field (Grottoli et al., 2025).\u003c/p\u003e\u003cp\u003eThe focus of this study was on the differences induced by the composition of the feed, but other factors including the amount of food and the frequency and timing of feeding may affect outcomes. We deliberately chose to supply the food treatments on a daily basis, given that corals in the reef have access to food regularly or near continuously. Compared to the majority of studies on heat stress and bleaching that do not or rarely supply food during experiments (Grottoli et al., 2021), the corals in our treatments are assumed to be fed closer to the point of satiation, mimicking field conditions more closely. This has downstream implications for the interpretation of our results. Given that it could be assumed that even suboptimal food composition at high density may have an enhancing effect on coral physiology, the differences between food treatments might be more nuanced with less or less frequent food supply during our experiment.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section2\"\u003e\u003ch2\u003ePhotosynthesis and respiration are similar between food types\u003c/h2\u003e\u003cp\u003ePhotosynthesis and respiration were stable throughout the experiment and within ranges previously reported for the species (Puntin et al., 2023; Vetter et al., 2024). While it has been reported that heterotrophic feeding and food availability enhance photosynthetic (Houlbr\u0026egrave;que \u0026amp; Ferrier-Pag\u0026egrave;s, 2009; Hoogenboom et al., 2010) and respiration rates (Borell et al., 2008; Dobson et al., 2021; Ferrier-Pag\u0026egrave;s et al., 2010) compared to starved corals, our results add that differences in the type of coral feed, i.e. its nutritional value, does not affect these variables. Whether food composition may play a role in modulating photosynthesis under more limited heterotrophic supply remains to be investigated.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec21\" class=\"Section2\"\u003e\u003ch2\u003eEffect of food types on heterotrophic compensation\u003c/h2\u003e\u003cp\u003eMetabolic rates were consistently higher in symbiotic fragments than in their bleached clones across all species. A reduction in calcification is one of the responses to bleaching stress, allowing corals to recover while maintaining a metabolic balance (Cohen \u0026amp; Holcomb, 2009; Dobson et al., 2021; Grottoli et al., 2017; Schoepf et al., 2015). However, the difference between bleached and symbiotic fragments strongly differed by species, with a positive correlation between the strength of the difference and the baseline productivity of the species. In the least productive species \u003cem\u003eG. fascicularis\u003c/em\u003e, differences were smallest and growth and respiration of bleached fragments were similar to that of symbiotic fragments with few exceptions. Heterotrophic feeding has previously been reported to benefit the growth of bleached corals (Towle et al., 2015; Tremblay et al., 2016) and given the overall low productivity of \u003cem\u003eG. fascicularis\u003c/em\u003e and its high heterotrophic food intake, all food treatments may have sufficed to compensate for the lack in autotrophic energy. In the intermediately productive \u003cem\u003eP. lobata\u003c/em\u003e symbiotic fragments had significantly higher growth and respiration rates than bleached corals and in the highly productive \u003cem\u003eS. pistillata\u003c/em\u003e, differences in growth between symbiotic and bleached fragments were approx. twice as large as in the other species. This result agrees with the assumptions that \u003cem\u003eS. pistillata\u003c/em\u003e assimilates less heterotrophic nutrients under bleaching stress (Ferrier-Pag\u0026egrave;s et al., 2010; Grottoli et al., 2017; Martinez et al., 2024; Tremblay et al., 2012), has a limited heterotrophic plasticity (Alamaru et al., 2009), and/or uses growth reduction as a strategy to maintain total energy reserves and biomass (Grottoli et al., 2017). However, because of the lack of a starved control in our design, we cannot unequivocally determine whether the differences between bleached and symbiotic fragments over species are distinct due to their inherent productivity, their heterotrophic capacity (their ability to assimilate nutrients heterotrophically), or their heterotrophic plasticity (their ability to switch flexibly between autotrophic and heterotrophic assimilation).\u003c/p\u003e\u003cp\u003eThe food treatments did not have a clear effect on the differences between bleached and symbiotic fragments. This was largely due to the similarity of their effects on bleached and symbiotic fragments, resulting in a relative null compensation between symbiotic states. However, the high complexity feed resulted in high physiological rates of bleached corals that were in range with the physiological rates of symbiotic corals supplied with low complexity feeds, further supporting the notion that high complexity feeds boost the physiology of bleached corals.\u003c/p\u003e\u003cp\u003eIn conclusion, while the benefit of heterotrophic nutrition on healthy corals varied between species, we showed that complex heterotrophic food sources benefit the physiology of all bleached corals, regardless of their baseline productivity or their heterotrophic capacity and plasticity. This highlights that incorporating diverse particulate and dissolved feed components into restoration, aquaculture, or field supplementation protocols could bolster coral resilience to the increasing frequency of mass-bleaching events.\u003c/p\u003e\u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eDeclaration of Competing Interest\u003c/h2\u003e\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThis study was conducted as part of the \u003cem\u003eOcean2100\u003c/em\u003e global change simulation project of the Colombian-German Center of Excellence in Marine Sciences (CEMarin) funded by the German Academic Exchange Service (DAAD). The work was made possible with the support of a scholarship from the German Academic Exchange Service (DAAD) to MAL.\u003c/p\u003e\u003ch2\u003eAuthor contributions\u003c/h2\u003e\u003cp\u003eMAL: Investigation, experiment, data collection, data analysis and writing. LH: experiment, data collection and data analysis. ME: experiment and data collection. MZ: Supervision, conceptualization, research materials, data analysis, writing, review and editing.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e\u003cp\u003eWe would like to thank the members of the Marine Holobiomics Lab for their support throughout the project, particularly Dr. Patrick Shubert and Christina Anding for technical support and animal caretaking.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData and R scripts used can be found online at:\u003c/p\u003e\u003cp\u003e\u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://github.com/Antonieta20/Heterotrophy-on-bleached-corals\u003c/span\u003e\u003cspan address=\"https://github.com/Antonieta20/Heterotrophy-on-bleached-corals\" targettype=\"URL\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAgostini, S., Fujimura, H., Higuchi, T., Yuyama, I., Casareto, B. 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Effects of yeast and yeast extract on growth performance, antioxidant ability and intestinal microbiota of juvenile Pacific white shrimp (\u003cem\u003eLitopenaeus vannamei\u003c/em\u003e). \u003cem\u003eAquaculture\u003c/em\u003e, \u003cem\u003e530\u003c/em\u003e, 735941. https://doi.org/10.1016/j.aquaculture.2020.735941\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"marine-biology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mabi","sideBox":"Learn more about [Marine Biology](https://www.springer.com/journal/227)","snPcode":"227","submissionUrl":"https://submission.nature.com/new-submission/227/3","title":"Marine Biology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Coral bleaching, coral physiology, heterotrophic feeding","lastPublishedDoi":"10.21203/rs.3.rs-6767958/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6767958/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eClimate change induced coral bleaching threatens the survival of coral reefs. The disruption of the symbiosis between corals and their photosymbionts during bleaching inhibits photosynthesis, the main source of energy of the coral holobiont. Yet, corals can supplement their metabolic demand through heterotrophic feeding and may partially compensate for the lack of autotrophic energy. However, the potential of different types of heterotrophic food to compensate for productivity loss during bleaching is not yet known. Therefore, we evaluated the effect of different food types on the physiology of symbiotic and bleached corals of three species (\u003cem\u003eGalaxea fascicularis\u003c/em\u003e, \u003cem\u003ePorites lobata\u003c/em\u003e, and \u003cem\u003eStylophora pistillata\u003c/em\u003e). Symbiotic and bleached fragments were exposed to five feeding treatments in a 21-week aquarium experiment that included combinations of dissolved and particulate feeds composed of thawed plankton, \u003cem\u003eArtemia salina\u003c/em\u003e nauplii, three phytoplankton species, honey, yeast, and amino acids. Here we show that in symbiotic \u003cem\u003eG. fascicularis\u003c/em\u003e and \u003cem\u003eP. lobata\u003c/em\u003e, growth was not affected by the different food types, while growth increased 1.5- to 2-fold in the high complexity feed in symbiotic \u003cem\u003eS. pistillata\u003c/em\u003e. In contrast, all bleached corals benefitted from richer diets. Complex feeds doubled to tripled growth parameters relative to dissolved or low-complexity feeds, and bleached \u003cem\u003eS. pistillata\u003c/em\u003e fragments fed only thawed plankton perished. Food treatments did not alter respiration or photosynthetic rates, indicating that growth gains stemmed from enhanced heterotrophic nutrient supply. Physiological rates were consistently higher in symbiotic fragments than in their bleached clones across all species and the differences increased with the baseline productivity of the species from \u003cem\u003eG. fascicularis\u003c/em\u003e over \u003cem\u003eP. lobata\u003c/em\u003e to \u003cem\u003eS. pistillata\u003c/em\u003e. However, the food treatments did not have a clear effect on the differences between bleached and symbiotic fragments. Our results demonstrate that incorporating diverse particulate and dissolved feed components into restoration, aquaculture, or field supplementation protocols could bolster coral resilience to the increasing frequency of mass-bleaching events.\u003c/p\u003e","manuscriptTitle":"Complex food sources aid physiological compensation of bleached corals","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-10 20:07:40","doi":"10.21203/rs.3.rs-6767958/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revise and Resubmit","date":"2025-08-25T07:45:37+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2025-07-13T02:10:37+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-09T01:01:10+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-30T13:45:27+00:00","index":"","fulltext":""},{"type":"submitted","content":"Marine Biology","date":"2025-05-28T08:08:37+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"marine-biology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"mabi","sideBox":"Learn more about [Marine Biology](https://www.springer.com/journal/227)","snPcode":"227","submissionUrl":"https://submission.nature.com/new-submission/227/3","title":"Marine Biology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"0e76b4a8-6dde-4bd5-902e-4fcee3c9412f","owner":[],"postedDate":"July 10th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-03-16T16:11:57+00:00","versionOfRecord":{"articleIdentity":"rs-6767958","link":"https://doi.org/10.1007/s00227-026-04806-9","journal":{"identity":"marine-biology","isVorOnly":false,"title":"Marine Biology"},"publishedOn":"2026-03-10 15:59:00","publishedOnDateReadable":"March 10th, 2026"},"versionCreatedAt":"2025-07-10 20:07:40","video":"","vorDoi":"10.1007/s00227-026-04806-9","vorDoiUrl":"https://doi.org/10.1007/s00227-026-04806-9","workflowStages":[]},"version":"v1","identity":"rs-6767958","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6767958","identity":"rs-6767958","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}