TRANSPORT OF BLUE-CRAB (CALLINECTES-SAPIDUS) LARVAE IN THE WATERS OFFMID-ATLANTIC STATES

General aspects of the life history of the blue crab (Callinectes sapi dus Rathbun) were described in the early part of the 20th century, but the larval biology of the species has remained enigmatic until recent ly. In the waters off the Mid-Atlantic States (MAB)(1), spawning occur s throughout the summer with a peak in late July and early August. Gra vid females migrate to the mouths of estuaries, and newly hatched larv ae are quickly exported to the adjacent shelf. Development through sev en zoea stages takes place in the open waters of the continental shelf and requires 4 to 5 weeks. Zoea larvae remain in surface waters, but not necessarily in the neuston, throughout development. Retention in t he MAB is controlled by wind-driven, northward-flowing water located b etween 20 and 60 km off the coast. This northward current is between a strong, southward coastal current that hugs the immediate shoreline a nd a more diffuse southward flow along the outer continental shelf. Re -invasion of the estuaries of the MAB occurs during the postlarval (me galopa) stage and is effected by southward wind events that occur in e arly fall. Ekman dow associated with these events raises sea level alo ng the coast and results in strong subtidal how into the estuaries. Se ttlement occurs in discrete, aperiodic pulses and does not necessarily occur in the parent estuaries. Thus, the apparent populations of C. s apidus in the various estuaries of the MAB are best described as one m etapopulation. Transport of C. sapidus megalopae into the estuary requ ires the coincident occurrence of a southward, along-shore wind event and a nearby patch of megalopae. The stochastic nature of this co-occu rrence explains the observed temporal variations in settlement of C. s apidus in the estuary.