Affiliation: College of Arts and Sciences, Department of Biology
Climate change is expected to increase the intensity and/or frequency of natural disturbances which are important drivers of coral reef community structure and functioning. Past work has often quantified the effect of singular, isolated events on living coral cover (mainly on pristine, high cover reefs), yet we know little about how disturbances affect coral community structure on contemporary, degraded reefs. Additionally, we know that disturbances, including hurricanes, coral bleaching, and coral disease, have the potential to interact, but we do not have a general understanding of the outcomes of these interactions on coral communities. Disturbances interact by altering the likelihood, extent, or severity of a subsequent event, or by altering the recovery time after the next event. These interactions have the potential to create novel or compound effects, which could affect coral community resilience.My dissertation work quantifies how disturbances drive changes in scleractinian coral communities through a framework that evaluates the impacts of disturbances as multiple, interacting events. First, I investigate the ecological conditions related to recent recovery of endangered elkhorn coral (Acropora palmata) and found that regrowth correlated strongly with healthy herbivore populations, particularly higher levels of Diadema antillarum. Second, I quantified the resilience (i.e. resistance and recovery) of contemporary Caribbean coral reefs to tropical storm impacts by compiling a regional database of coral surveys from ~2000 unique reef locations between 1970-2017. I found that coral reef communities are becoming more resistant to storm damage (i.e. less immediate coral loss), but are not recovering to pre-disturbance states. The number of historical storms a particular reef experienced is a significant predictor of decreased recovery and increased resistance, suggesting that multiple disturbance events can influence resilience capacity. Additionally, if recovery time becomes limited with more frequent disturbances, understanding reef resistance may give us greater insight into which reefs can persist under predicted changes to disturbance regimes. Third, I tested hypotheses of disturbance interactions between hurricanes, coral bleaching, and coral disease events and found mixed evidence of these interactions across broader temporal and spatial scales. Lastly, I consider the context in which we communicate and quantify changes to coral condition by developing site-appropriate baselines to use in coral reef reporting indices.