High-latitude marginal reefs support fewer but bigger corals than their tropical counterparts
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Anthropogenic impacts are typically detrimental to tropical coral reefs, but the effect of increasing environmental stress and variability on the size structure of coral communities remains poorly understood. This limits our ability to effectively conserve coral reef ecosystems because size specific dynamics are rarely incorporated. Our aim is to quantify variation in the size structure of coral populations across 20 sites along a tropical-to-subtropical environmental gradient on the east coast of Australia (~ 23 to 30°S), to determine how size structure changes with a gradient of sea surface temperature, turbidity, productivity and light levels. We use two approaches: 1) linear regression with summary statistics (such as median size) as response variables, a method frequently favoured by ecologists and 2) compositional functional regression, a novel method using entire size?frequency distributions as response variables. We then predict coral population size structure with increasing environmental stress and variability. Together, we find fewer but larger coral colonies in marginal reefs, where conditions are typically more variable and stressful, than in tropical reefs. Our model predicts that coral populations may become gradually dominated by larger colonies (> 148 cm2) with increasing environmental stress. Fewer but bigger corals suggest low survival of smaller corals, slow growth, and/or poor recruitment. This finding is concerning for the future of coral reefs, as it implies that current marginal populations, or future reefs in increasingly stressful environmental conditions may have low recovery potential. We highlight the importance of continuously monitoring changes to population structure over biogeographic scales.
Chong , F , Sommer , B , Stant , G , Verano , N , Cant , J , Lachs , L , Johnson , M L , Parsons , D R , Pandolfi , J M , Salguero-Gómez , R , Spencer , M & Beger , M 2023 , ' High-latitude marginal reefs support fewer but bigger corals than their tropical counterparts ' , Ecography . https://doi.org/10.1111/ecog.06835
Copyright © 2023 The Authors. Ecography published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
DescriptionFC is supported by the Panorama Doctoral Training Partnership (NE/S007458/1), the University of Hull and a JSPS London short-term pre-doctoral fellowship (PE22726). We acknowledge funding from the Australian Research Council Centre of Excellence for Environmental Decisions (CE110001014), an EU Marie Skłodowska-Curie Fellowship (TRIM-DLV-747102), and a Winifred Violet Scott Estate grant to MB; a CSIRO top-up scholarship, an Australian Research Council Discovery Early Career Research Award (DE230100141), a University of Sydney Fellowship and a Chancellor's Postdoctoral Research Fellowship from the University of Technology Sydney to BS. Fieldwork was further supported by two Australian Research Council Centre of Excellence awards (CE0561435 and CE140100020) to JMP and others.
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