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1. Complex interactions with nutrients and sediment alter the effects of predation on a reef‐building coral

   https://doi.org/10.1111/maec.12670  

   Rice, Mallory M.; Baldwin, Daniel G.; Fischer, Janine N.; Fuchs, Corinne; Burkepile, Deron E. (June 2021, Marine Ecology)

   Abstract Framework‐building corals create the three‐dimensional structure of coral reefs and are subject to predation from fishes, echinoderms, and gastropods. Anthropogenic stressors can magnify the effects of such top‐down pressure on foundation species. The gastropodCoralliophilaviolacea(Kiener, 1836) depletes coral energy reserves via predation, potentially increasing coral susceptibility to land‐based pollution (i.e., sediment accumulation and nutrient pollution). We hypothesized that sedimentation would worsen coral mortality, while nutrient enrichment would mitigate the harmful effects of sediment and predation on coral mortality by increasing the densities of algal symbionts. To test these hypotheses, we conducted in situ surveys of the fringing reefs in Mo'orea, French Polynesia to explore the relationships among massivePoritesspp. cover,C. violaceadensities, and sediment accumulation on coral colonies across low and high nutrient sites. We also conducted a factorial field experiment to test the interactions among these stressors on coral tissue mortality, symbiont densities, and chlorophyll. MassivePoritescolonies at higher nutrient sites hadC. violaceadensities 13 times higher than at low nutrient sites but there was no difference in the amount of live tissue on coral colonies with or without snails among these sites. In our experiment, there were interactions between predation and nutrients as well as nutrients and sediment that impacted coral mortality. Sedimentation and predation byC. violaceaincreased coral tissue mortality independently by ~20%. Nutrient enrichment reduced this effect in corals under sedimentation or predation pressure by lowering coral tissue mortality by 18% and increasing algal symbiont densities by ~28%. Our results indicate that sediment does not magnify top‐down pressure on this coral, and that moderate nutrient enrichment may interact with predation in complex, unexpected ways to alter the responses of corals to top‐down pressure. 

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2. Coral calcification responses to the North Atlantic Oscillation and coral bleaching in Bermuda

   https://doi.org/10.1371/journal.pone.0241854  

   Courtney, Travis A.; Kindeberg, Theodor; Andersson, Andreas J. (November 2020, PLOS ONE)

   Caroselli, Erik (Ed.)

   The North Atlantic Oscillation (NAO) has been hypothesized to drive interannual variability in Bermudan coral extension rates and reef-scale calcification through the provisioning of nutritional pulses associated with negative NAO winters. However, the direct influence of the NAO on Bermudan coral calcification rates remains to be determined and may vary between species and reef sites owing to implicit differences in coral life history strategies and environmental gradients across the Bermuda reef platform. In this study, we investigated the connection between negative NAO winters and Bermudan Diploria labyrinthiformis , Pseudodiploria strigosa , and Orbicella franksi coral calcification rates across rim reef, lagoon, and nearshore reef sites. Linear mixed effects modeling detected an inverse correlation between D . labyrinthiformis calcification rates and the winter NAO index, with higher rates associated with increasingly negative NAO winters. Conversely, there were no detectable correlations between P . strigosa or O . franksi calcification rates and the winter NAO index suggesting that coral calcification responses associated with negative NAO winters could be species-specific. The correlation between coral calcification rates and winter NAO index was significantly more negative at the outer rim of the reef (Hog Reef) compared to a nearshore reef site (Whalebone Bay), possibly indicating differential influence of the NAO as a function of the distance from the reef edge. Furthermore, a negative calcification anomaly was observed in 100% of D . labyrinthiformis cores in association with the 1988 coral bleaching event with a subsequent positive calcification anomaly in 1989 indicating a post-bleaching recovery in calcification rates. These results highlight the importance of assessing variable interannual coral calcification responses between species and across inshore-offshore gradients to interannual atmospheric modes such as the NAO, thermal stress events, and potential interactions between ocean warming and availability of coral nutrition to improve projections for future coral calcification rates under climate change. 

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3. Ocean acidification modulates material flux linked with coral calcification and photosynthesis

   https://doi.org/10.1038/s41598-025-30818-4  

   Armstrong, David A; McNicholl, Conall; Bahr, Keisha D (December 2025, Scientific Reports)

   Abstract Coral reefs are essential for the foundation of marine ecosystems. However, ocean acidification (OA), driven by rising atmospheric carbon dioxide (CO₂) threatens coral growth and biological homeostasis. This study examines two Hawaiian coral species—Montipora capitataandPocillopora acutato elevated pCO₂simulating OA. Utilizing pH and O₂microsensors under controlled light and dark conditions, this work characterized interspecific concentration boundary layer (CBL) traits and quantified material fluxes under ambient and elevated pCO₂. The results of this study revealed that under increased pCO₂,P. acutashowed a significant reduction in dark proton efflux, followed by an increase in light O₂flux, suggesting reduced calcification and enhanced photosynthesis. In contrast,M. capitatadid not show any robust evidence of changes in either flux parameters under similar increased pCO₂conditions. Statistical analyses using linear models revealed several significant interactions among species, treatment, and light conditions, identifying physical, chemical, and biological drivers of species responses to increased pCO₂. This study also presents several conceptual models that correlate the CBL dynamics measured here with calcification and metabolic processes, thereby justifying our findings. We indicate that elevated pCO₂exacerbates microchemical gradients in the CBL and may threaten calcification in vulnerable species such asP. acuta, while highlighting the resistance ofM. capitata. Therefore, this study advances our understanding of how interspecific microenvironmental processes could influence coral responses to changing ocean chemistry. 

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4. The trace metal economy of the coral holobiont: supplies, demands and exchanges

   https://doi.org/10.1111/brv.12922  

   Reich, Hannah G.; Camp, Emma F.; Roger, Liza M.; Putnam, Hollie M. (November 2022, Biological Reviews)

   ABSTRACT The juxtaposition of highly productive coral reef ecosystems in oligotrophic waters has spurred substantial interest and progress in our understanding of macronutrient uptake, exchange, and recycling among coral holobiont partners (host coral, dinoflagellate endosymbiont, endolithic algae, fungi, viruses, bacterial communities). By contrast, the contribution of trace metals to the physiological performance of the coral holobiont and, in turn, the functional ecology of reef‐building corals remains unclear. The coral holobiont's trace metal economy is a network of supply, demand, and exchanges upheld by cross‐kingdom symbiotic partnerships. Each partner has unique trace metal requirements that are central to their biochemical functions and the metabolic stability of the holobiont. Organismal homeostasis and the exchanges among partners determine the ability of the coral holobiont to adjust to fluctuating trace metal supplies in heterogeneous reef environments. This review details the requirements for trace metals in core biological processes and describes how metal exchanges among holobiont partners are key to sustaining complex nutritional symbioses in oligotrophic environments. Specifically, we discuss how trace metals contribute to partner compatibility, ability to cope with stress, and thereby to organismal fitness and distribution. Beyond holobiont trace metal cycling, we outline how the dynamic nature of the availability of environmental trace metal supplies can be influenced by a variability of abiotic factors (e.g. temperature, light, pH, etc.). Climate change will have profound consequences on the availability of trace metals and further intensify the myriad stressors that influence coral survival. Lastly, we suggest future research directions necessary for understanding the impacts of trace metals on the coral holobiont symbioses spanning subcellular to organismal levels, which will inform nutrient cycling in coral ecosystems more broadly. Collectively, this cross‐scale elucidation of the role of trace metals for the coral holobiont will allow us to improve forecasts of future coral reef function. 

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5. Divergent responses of the coral holobiont to deoxygenation and prior environmental stress

   https://doi.org/10.3389/fmars.2023.1301474  

   Swaminathan, Sara D.; Meyer, Julie L.; Johnson, Maggie D.; Paul, Valerie J.; Bartels, Erich; Altieri, Andrew H. (February 2024, Frontiers in Marine Science)

   Ocean deoxygenation is intensifying globally due to human activities – and is emerging as a grave threat to coral reef ecosystems where it can cause coral bleaching and mass mortality. However, deoxygenation is one of many threats to coral reefs, making it essential to understand how prior environmental stress may influence responses to deoxygenation. To address this question, we examined responses of the coral holobiont (i.e., the coral host, Symbiodiniaceae, and the microbiome) to deoxygenation in corals with different environmental stress backgrounds. We outplantedAcropora cervicornisfragments of known genotypes from anin situnursery to two sites in the Florida Keys spanning an inshore-offshore gradient. After four months, fragments from the outplanted corals were transferred to the laboratory, where we tested differences in survivorship, tissue loss, photosynthetic efficiency, Symbiodiniaceae cell density, and coral microbiome composition after persistent exposure to one of four oxygen treatments ranging from extreme deoxygenation (0.5 mg L^-1) to normoxia (6 mg L^-1). We found that, for the short duration of exposure tested in this study (four days), the entire coral holobiont was resistant to dissolved oxygen (DO) concentrations as low as 2.0 mg L^-1, but that the responses of members of the holobiont decoupled at 0.5 mg L^-1. In this most extreme treatment, the coral host showed decreased photosynthetic efficiency, tissue loss, and mortality, and lower Symbiodiniaceae densities in a bleaching response, but most microbial taxa remained stable. Although deoxygenation did not cause major community shifts in microbiome composition, the population abundance of some microbial taxa did respond. Site history influenced some responses of the coral host and endosymbiont, but not the coral microbiome, with corals from the more stressful inshore site showing greater susceptibility to subsequent deoxygenation. Our study reveals that coral holobiont members respond differently to deoxygenation, with greater sensitivity in the coral host and Symbiodiniaceae and greater resistance in the coral microbiome, and that prior stress exposure can decrease host tolerance to deoxygenation. 

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