Unraveling coral nutrition strategies in response to nuisance macroalgae: insights from amino acid isotopic analysis in the Northwestern Hawaiian Islands
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2024
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Abstract
Coral reef ecosystems are under increasing threat from local and global stressors, including the introduction and proliferation of invasive species. Understanding coral nutrition strategies in response to environmental stress is crucial for predicting reef resilience. This study investigates the impact of macroalgal cover, specifically the nuisance red alga Chondria tumulosa, on nutritional strategies of two corals (Montipora capitata, Pocillopora spp.) in the Northwestern Hawaiian Islands (NWHI). Coral samples were collected pre- and post-invasion of C. tumulosa, with bulk tissue and compound-specific isotopic analysis of amino acids (CSIA-AA) employed to assess coral nutrition. Bulk carbon and nitrogen stable isotopic compositions (δ13C, δ15N) revealed coupled nutritional reliance between coral host and symbiont with a consistent δ13C decrease with depth. CSIA-AA demonstrated significant separation in essential amino acid δ13C fingerprints between coral hosts, symbionts, plankton, and C. tumulosa relating to autotrophic fidelity in M. capitata and trophic plasticity in Pocillopora consistent with previous work. Trophic position (TPGlx-Phe) of plankton was 2.3±0.6, consistent with primary consumers, while coral TPGlx-Phe indicate high reliance on autotrophy in M. capitata (TPGlx-Phe: 1.1±0.2) and greater heterotrophic feeding on plankton in Pocillopora spp. (TPGlx-Phe: 1.6±0.4). A higher-than-expected TPGlx-Phe was found in C. tumulosa (1.5±0.1), suggesting inclusion of heterotrophic bacteria living on or among the macroalgae. It is unlikely that Pocillopora spp. obtained nutrition directly from C. tumulosa, however, our work suggests that essential amino acid δ13C values can be used to identify organisms that prey on C. tumulosa. These findings underscore the importance of understanding coral-algal interactions in the face of environmental change and highlight the utility of CSIA-AA in elucidating complex trophic dynamics within coral reef ecosystems.
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Biological oceanography, Chondria tumulosa, Coral, Isotopes, Northwestern Hawaiian Islands
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62 pages
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