Understanding and predicting disturbances on coral reefs at multiple spatial scales
thesisposted on 2022-03-28, 19:13 authored by Joseph Maina Mbui
Understanding and predicting the vulnerability of coral reefs to disturbances that act at multiple scales is of paramount importance for guiding reef conservation initiatives. This thesis presents a series of studies that combined large environmental and ecological datasets with a broad range of quantitative tools in order to address questions about coral reef vulnerability around the world. First, I combined global spatial gradients of coral exposure to radiation stress factors (temperature, UV light and doldrums), stress-reinforcing factors (sedimentation and eutrophication), and stress-reducing factors (temperature variability and tidal amplitude) to produce a global map of coral exposure and identify areas where exposure depends on factors that can be locally managed. I show that exposure of coral reefs could be reduced by locally managing chronic human impacts (sedimentation and eutrophication) that exacerbate thermal stress. Using this first study as a roadmap, I then explore thermal stress adaptation and/or acclimation mechanisms in corals. Here, using environmental data and a biogeographic database of common Symbiodinium clades living in scleractinian corals, I establish the climatic gradients separating niches among these clades and developed geographical estimates of where corals are likely to acquire thermally compatible symbiont clades in order for them to compensate for increasing temperature. Finally, to explore sedimentation in greater detail, I model hydrological linkages among coastal watersheds and near shore reefs, and subsequently the relative affects of local land use manipulation versus global climate change on sediment dynamics. The results corroborate the hypothesis that there are strong linkages between watersheds' climate variability, hydrology, forest cover, population growth and the adjacent coral reefs. Moreover, the analyses suggest that regional land use management is far more important for influencing sedimentation rates in tropical reefs (such as Madagascar), than mediating climate change. All in all, I demonstrate a need and a framework for conservation science to focus research and management efforts on incorporating the factors that mitigate the effects of coral stressors, and that enhance ecological resilience, until long-term carbon reductions are achieved through global negotiations.