Transport of Blue Crab (Callinectes Sapidus) Larvae in the Waters Off Mid-Atlantic States

General aspects of the life history of the blue crab (Callinectes sapidus Rathbun) were described in the early part of the 20th century, but the larval biology of the species has remained enigmatic until recently. In the waters off the Mid-Atlantic States (MAB), spawning occurs throughout the summer with a peak in late July and early August. Gravid females migrate to the mouths of estuaries, and newly hatched larvae are quickly exported to the adjacent shelf. Development through seven 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 the MAB is controlled by wind-driven, northward-flowing water located between 20 and 60 km off the coast. This northward current is between a strong, southward coastal current that hugs the immediate shoreline and a more diffuse southward flow along the outer continental shelf. Re-invasion of the estuaries of the MAB occurs during the postlarval (megalopa) stage and is effected by southward wind events that occur in early fall. Ekman flow associated with these events raises sea level along the coast and results in strong subtidal flow into the estuaries. Settlement occurs in discrete, aperiodic pulses and does not necessarily occur in the parent estuaries. Thus, the apparent populations of C. sapidus in the various estuaries of the MAB are best described as one metapopulation. Transport of C. sapidus megalopae into the estuary requires the coincident occurrence of a southward, along-shore wind event and a nearby patch of megalopae. The stochastic nature of this co-occurrence explains the observed temporal variations in settlement of C. sapidus in the estuary.