Anthropogenic influences are altering top-down and bottom-up processes on ecosystems worldwide. On coral reefs, overfishing results in reductions in top-down control by fishes that eat algae and fishes that eat corals. Many of these reefs are also exposed to increased levels of inorganic nutrients from agriculture or coastal development. Changes in top-down and bottom-up processes can alter the outcome of competitive interactions between corals and macroalgae, but how these interactions relate to changes in community trajectories on coral reefs is not well understood. Using a long-term experiment, my work investigates how reductions in herbivory and increases in the availability of inorganic nutrients alter community development on coral reefs.
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Coral-killing disturbances (e.g., cyclones, bleaching events, etc.) are commonplace on coral modern coral reefs. Following disturbances, some reefs regain coral cover quickly whereas others recover slowly or fail to recover. My work uses time-series data from the Moorea Coral Reef LTER to identify mechanisms that drive different rates of coral recovery after disturbance. My work points to processes that affect the survival of corals shortly after settlement that likely determine the recovery rate of coral communities.
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Processes that determine the success of early life stages of corals can have strong impacts on coral reef communities. Corals are sessile animals, but their larvae make active habitat selection choices that can determine their future competition, growth, and survival to adulthood. My work has shown that coral larvae make complex settlement choices at the scale of millimeters (Speare et al. In press). Additionally, sediment trapped in algal turfs, which is commonly found on degraded coral reefs, can strongly suppress coral settlement rates (Speare et al. 2019)
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Marine heatwaves are the defining challenge to coral reefs in the Anthropocene. However, the impacts of marine heatwave are heterogeneous across the seascape and within coral communities. My work investigates factors that determine the winners and losers during marine heatwaves. We showed the both the largest corals and the smallest coral recruits are the most vulnerable to mortality during bleaching events. This work suggests that bleaching events may undermine the recovery potential of coral reefs by disproportionately affecting the corals most important for recovery (Speare et al. 2022).
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