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Contributed Talk

Session: : Communities: Disturbance And Recovery 2

COS 32-3 - CANCELLED - Coral symbioses under multiple stressors: Record-breaking heatwave drives symbiont co-dominance and cryptic diversity losses

Monday, August 7, 2023
4:00 PM – 4:15 PM PDT
Location: B113
Abstract: Climate change-amplified marine heatwaves pose the greatest threat globally to the future of coral reefs. Simultaneously, coral reefs are ubiquitously exposed to varying degrees of human disturbance, such as fishing or pollution. The Pacific Island of Kiritimati harbours reefs along a gradient of local human disturbance and was the epicentre for the 2015-2016 global coral bleaching event, making Kiritimati a microcosm representative of the coral reef crisis. The algal symbionts (family Symbiodiniaceae) hosted by corals often have dramatic consequences for their survival through heatwaves. Here we report symbiont metabarcoding from coral samples taken over 5 years spanning the heatwave (n=1,270) from tagged colonies of 7 species across different families and life-history strategies, at sites exposed to varying levels of human disturbance. Variation in the alpha and beta diversity of partners has previously been reported for coral and symbiont species but not yet across a major stress event, such as a heatwave. Upon heatwave recovery, more corals simultaneously hosted symbionts from competing genera than before the heatwave; but this effect diminished with increasing exposure to local disturbance. Yet at the community level, widespread partner changes from phylogenetically and functionally more diverse Cladocopium spp. to ostensibly thermotolerant Durusdinium spp. resulted in significant declines in symbiont metacommunity richness. This natural experiment on a symbiotic model system addresses foundational ecological debates surrounding contrasting effects of disturbance on macro- and micro-organism diversity and effects of local disturbance protection on climate change vulnerability, with clear implications for predicting and managing coral resilience in an increasingly disturbed ocean.