The Distribution of Blue Crab (Callinectes sapidus) Megalopae at the Mouths of Chesapeake and Delaware Bays: Implications for Larval Ingress

Abstract

Transport of Callinectes sapidus (blue crab) megalopae from the continental shelf into estuaries may influence recruitment variability of this species. Observations of the vertical distribution of C. sapidus megalopae near the mouths of Chesapeake and Delaware Bays were used to infer vertical swimming behaviors that may influence ingress to these estuaries. Megalopae and oceanographic conditions were sampled at locations from ~10 km inshore of the estuary mouths to ~40 km offshore in coastal shelf waters on September 7–13, 2005 and September 3–7, 2006. Megalopae were present in greater abundance and at shallower depths during night compared to day at all locations in Chesapeake and Delaware Bays, suggesting that megalopae make diel vertical migrations within the estuary and on the continental shelf near the estuarine mouths. Within the mouth of the estuaries, only limited evidence suggests that megalopae increase in abundance in the upper water column during nocturnal flood tides in Delaware Bay. These findings suggest that wind forcing and density-induced subtidal flows are more likely mechanisms for ingress to Chesapeake and Delaware Bays than tidal transport.