Blue crab larval dispersion and retention in the Mississippi Bight: Testing the hypothesis

An hypothesis relating physical forcing to dispersion and retention of blue crab larvae was tested in the area of the Mississippi Bight. Seasonal circulation patterns derived from a 3-dimensional, primitive equation, sigma-coordinate model of the Gulf of Mexico (GOM) indicate favorable conditions for offshore dispersal of larvae and their return to nearshore waters as megalopae occur between April and October. Large basin-scale events, such as Loop Current intrusions into the GOM with spin-off eddy generation and anomalies in average wind stress may interrupt this circulation pattern and change the settlement success rate. Meteorological and hydrological factors thought to influence settlement were compared to daily records of megalopal abundance in Mississippi Sound for the years 1991 through 1999. Wind stress was strongly correlated with settlement success. Eastward wind stress during the months of July and August, when the larvae are at sea, and westward wind stress during recruitment in September and October were important in retaining larvae in the general area and subsequently returning them near shore as megalopae, respectively. Northward intrusion of the Loop Current and warm core ring detachment during late summer altered circulation patterns and decreased settlement success.