Local scale hydrodynamics and oxygen fluctuations near coral reefs

Abstract

Coral reefs are a vital part of Curaçao’s economy, providing revenue from ecotourism and fisheries, as well as providing shoreline protection. A vital coral species, Diploria strigosa, is a major reef-building species around the island, and contributes enormously to the health of the reefs, making it a prime candidate for this project. Physical oceanic processes, such as waves and currents, influence the health of these corals by introducing oxygen-rich water through mixing of the water column. In order to understand more about the growth and vitality of coral around Curaçao, it is therefore critical to understand how these processes influence the movement of oxygen around coral reefs. This thesis set out to collect field data to investigate the existence of a relationship between hydrodynamics and dissolved oxygen near coral reefs around the island of Curaçao, as part of a larger project, the SEALINK project. SEALINK, part of the Dutch Research Council (NWO)’s Caribbean Research program, is an interdisciplinary research initiative to assess the impact of land-based and water-borne substances on the coral reefs of the Dutch Caribbean. Through a fieldwork campaign, dissolved oxygen concentration, wave data, and current velocity data was collected from seven study sites on the southern coast of Curaçao. Acoustic Doppler current profilers (AD2CP) and oxygen loggers were deployed through diving, and left on the seafloor to measure for six hours. A statistical analysis was run to test the validity of using current velocities as a predictor for dissolved oxygen values. Finally, a computational fluid dynamics (CFD) model was created using the fieldwork data in order to assist in the understanding of processes that influence dissolved oxygen around coral reefs. The results from fieldwork show that the extent of the relationship between waves, currents, and dissolved oxygen depends greatly on the location and tidal cycle. Study sites closer to the eastern point of the island showed that velocity and dissolved oxygen are connected, and that velocity has a greater capacity to predict dissolved oxygen values. The CFD model assists in a deeper comprehension of the influence of flow and other processes that can impact dissolved oxygen fluctuations around coral reefs.