Eastern Caribbean Circulation and Island Mass Effect on St. Croix, US Virgin Islands: A Mechanism for Relatively Consistent Recruitment Patterns

The northeastern Caribbean Sea is under the seasonal influence of the Trade Winds but
also of the Orinoco/Amazon freshwater plume. The latter is responsible for intensification of
the Caribbean Current in general and of its eddy activity in the northern part of the Caribbean
Sea. More importantly, we show in this study that the front of the freshwater plume
drives a northward flow that impinges directly on the island of St. Croix in the United States
Virgin Islands. The angle of incidence of the incoming flow controls the nature of the wake
on both sides and ends of the island, which changes from cyclonic to anticylonic wake flow,
with either attached or shed eddies. Using an off-line bio-physical model, we simulated the
dispersal and recruitment of an abundant Caribbean coral reef fish, the bluehead wrasse
(Thalassoma bifasciatum) in the context of the wake flow variability around St. Croix. Our
results revealed the role played by the consistent seasonal forcing of the wake flow on the
recruitment patterns around the island at the interannual scale. The interannual variability of
the timing of arrival and northward penetration of the plume instead controls the nature of
the wake, hence the regional spatial recruitment patterns.