UBC Theses and Dissertations
Shedding light on the future of Caribbean coral reefs under climate change Maharaj, Ravi Rajesh
Coral reefs are important ecologically and socially but are threatened by local human impacts and future global climate change. Effective management promotes climate resilience but must take into account the unique multi-scale characteristics of coral reef ecosystems. This dissertation assessed historic trends in coral reef fish assemblages across the Caribbean, to determine the impacts of climate change and role of key environmental drivers in shaping these trends and investigated the influence of these drivers on future reef fish biodiversity. Firstly, using ecosystem indicators, I analyzed historical fisheries catches to assess the potential effects of ocean warming and habitat availability on Caribbean reef fish assemblages. I found that changes in community assemblages were higher than global average for all tropical fisheries and could be explained by increases in sea surface temperature and fishing effects. A negative interaction between reef habitats in each country and sea surface temperature in relation to changes in catch composition, suggesting that habitats may reduce the sensitivity of fish communities to warming. Secondly, using species distribution models, I projected changes in coral reefs under climate change in terms of their morphological complexity. Results showed that under a no-mitigation scenario reef complexity declines significantly, with the most morphologically complex species, Acropora sp., showing northward shifts in relative prevalence. Finally, I conducted multi-scale comparisons of the influence of reef complexity with other environmental variables on current and future Caribbean reef fish biodiversity. Reef fishes showed an affinity for higher temperatures, primary productivity and lower dissolved oxygen at the global scale, but tended toward more alkaline areas hosting reefs, with species showing mixed affinities toward dissolved oxygen. Regional models projected more rapid declines in biodiversity, though declines from global models were larger. Global and regional models projected similar magnitudes of range expansion, though invasions were projected mainly in higher latitudes for global models while regional models projected invasions in lower latitudes around reef-associated areas. Overall, my thesis provides new knowledge for climate-resilient conservation planning by highlighting the utility of multi-scale approaches and the role coral reef habitats may play in protecting reef fish assemblages against the impacts of climate change.
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