Blue crab larval dispersion and retention in the Mississippi Bight

A conceptual hypothesis relating physical forcing to dispersion and retenti on was developed for blue crab larvae within the Mississippi Eight. The spa wning period for blue crabs in the northern Gulf of Mexico is protracted. H atching of eggs occurs near the barrier islands and mouths of coastal bays from March through October. Larvae are released on ebbing tides and spend t he next 30 to 50 d offshore where they develop through seven zoeal stages b efore undergoing metamorphosis to megalopae. Duration of the megalopal stag e is variable but generally persists from 6 to 20 d. Blue crabs recruit to Gulf estuaries as megalopae. During the critical planktonic phase in their life history, larvae are subject to the vagaries of seasonal circulation pa tterns which can either return them to nearshore where they can successfull y settle, or lose them at sea. Archived currents from a 3-dimensional, prim itive equation, sigma-coordinate model of the Gulf of Mexico, driven by cli matological winds and damped to surface salinity and temperature, were used to study advection of blue crab larvae in the Mississippi Eight. Data sugg est that seasonal circulation patterns driven by average wind stress provid e a window of opportunity for blue crab larval dispersion offshore and retu rn nearshore during the appropriate period in their development for settlem ent as megalopae. in the Mississippi Eight, this window usually occurs betw een April and October. Large basin-scale events, such as Loop Current intru sions and spin-off eddy generation, may interrupt this circulation pattern and change the settlement success rate. Variations in the seasonal forcing, due to anomalous winds, or basin-scale events may contribute to fluctuatio ns in levels of harvestable adult blue crabs.