TIDAL VARIABILITY IN CORAL REEF HYDRODYNAMICS AND TURBIDITY: IMPLICATIONS FOR SEA LEVEL RISE

Coral reefs are ecologically important for their biodiversity and role in the ocean food web. They are also important for local economies due to tourism and the revenue that it generates. Coral reefs have a history of adapting to a changing environment. Having survived various shifts in sea level and climate, while other times failing to adapt, it is important to understand these processes and try to define their limits. Studies have shown that sedimentation is a threat to coral reefs that can result in their deterioration, which may result from a changing climate via increasing storm intensities and frequencies, adding sediment to nearshore waters by increasing terrestrial run-off, shoreline erosion and resuspension of particles. Storms also cause hydrodynamic disturbances, which can be responsible for the breakage of fragile corals and can alter the distribution of different coral species. Increasing sea levels may cause the coral reefs to change their effectiveness in wave energy dissipation, causing retreating shorelines and may also drown coral reefs that cannot keep pace with rising seas. An increase in sea level may cause shifts in the hydrodynamics of the lagoon, altering the flushing of water and overall quality. With sea level predictions showing a rapid increase, studies should be conducted immediately to establish benchmarks for future research and comparative analysis to quantify the potential deterioration.

This study was conducted on the southeastern side of Buck Island Reef National Monument, a microtidal Acropora palmata-dominated barrier reef system located 2 km NE of St. Croix, USVI. The tidal variation was used as a proxy for sea level rise scenarios. The purpose of this study was to quantify current velocities and energy dissipation by a barrier reef. Using pressure sensors to measure water surface fluctuations, results show that wave energy dissipation is tidally dependent with more energy associated with higher tides. Using Aquadopp current profilers, the magnitude of the lagoonal currents and flushing appear to be wave driven and tidally dependent. Depth integrated water samples were obtained in the lagoon to determine suspended sediment concentrations. Collectively, these data indicate that sea level rise will impact the hydrodynamics of reef systems and sediment transport processes.