Date of Award

1-1-2013

Document Type

Open Access Thesis

Department

Marine Science

First Advisor

Jean T Ellis

Abstract

The modern framework of Caribbean coral reefs is a product of resilient structures that have survived extreme variations in sea level for the past 18,000 years. However, the added influences of anthropogenic pressures, including ocean acidification, overfishing, pollution and bleaching make the future response to sea level rise uncertain. Carbonate production in the Caribbean is no longer at these historic rates and reefs may not be able to keep pace with the projected increases in sea level. This could have dramatic impacts on the hydrodynamics in coral reef environments, as reef morphology strongly influences these processes. Coral reefs are regarded as natural breakwaters and in turn, shoreline protective structures. If a reef is not at a sufficient height in comparison to the water level, wave energy dissipation is diminished and more energy is transferred to the shoreline, resulting in increased shoreline erosion. Wave driven flows are important in reef environments and it should be expected to see resultant changes in flow associated with various energy regimes, altering lagoonal flushing, water quality and nutrient uptake.

This study was conducted on the southeastern side of Buck Island Reef National Monument, a microtidalAcropora palmata-dominated barrier reef system located 2 km NE of St. Croix, USVI. Tidal variability in energy dissipation and current velocities was used to represent future sea level conditions assuming a static reef system. Using Wave Height Pressure Sensors (WHPS) to measure water surface fluctuations, results show that wave energy dissipation is tidally dependent with approximately 20% less dissipation at higher tides. Using Aquadopp current profilers (AQD), the magnitude of lagoon currents and flushing appear to be wave driven and tidally dependent, with current velocities ranging from 35 cm s-1at low tide and 15 cm s-1at high tide. High tide conditions could be representative of a low tide scenario at an increased sea level of 0.4 m, which is within the range of the 2100 IPCC AR4 projections. Accordingly, the results of this study suggest that sea level rise will have substantial impacts to the hydrodynamics of reef systems, sediment transport processes and coral community structures.

Rights

© 2013, Chelsea Wegner

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