The impact of carbonate chemistry on bioeroding sponges and the persistence of south Florida coral reefs

Coral reef ecosystems are being threatened by the growing effects of anthropogenically-induced climate change. At a global-scale, diminished reef development and growth potential has culminated in a consequential shift towards the net loss of reef habitat. While the impacts of climate change have been well established for reef calcifiers, the response by bioeroders is vastly understudied in the literature.      

This Ph.D project evaluated the impacts of ocean acidification (OA) and diurnal carbonate chemistry variability on zooxanthellate (C. varians) and azooxanthellate (P. lampa and C. delitrix) sponge species common to Caribbean reef ecosystems. Physiological and molecular analysis identified a sponge stress response under OA conditions, as depressed bioerosion rates and differentially expressed genes implicated in a generalized stress response were measured in the 7.75 pH treatment. Diurnal carbonate chemistry variability was also found to be a significant driver of sponge bioerosion, with higher bioerosion rates measured under both contemporary and OA variable conditions relative to that of the static treatment groups, an effect that was more pronounced for the zooxanthellate sponge species.      

Additionally, this Ph.D project used a carbonate budget approach to evaluate spatial and temporal trends in reef growth potential for 723 South Florida reef sites. The results reported a net erosional state for coral reefs throughout the Florida Reef Tract (FRT). While these data detailed a considerable trend towards habitat loss throughout South Florida, the inclusion of reef type data revealed that mid-channel reefs in the Upper and Lower Keys may be potential hold-outs for reef development compared to their inshore and offshore counterparts.      

Altogether, the conclusions drawn from these studies address critical research gaps related to sponge bioerosion and reef development. This Ph.D will enhance prospective evaluations of habitat growth potential and improve future assessments modeling the fate of coral reef ecosystems in response to projected environmental scenarios.

Morris, J. T., 2022. The impact of carbonate chemistry on bioeroding sponges and the persistence of south Florida coral reefs. PhD thesis, University of Miami. 173 p. Thesis.

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