Ingress of Blue Crab Megalopae in the York River, Virginia, 1987–1989

Following larval development in coastal waters, the megalopa (postlarva) of the blue crab (Callinectes sapidus) enters estuaries and colonizes juvenile habitats. In Chesapeake Bay, blue crab abundance exhibits considerable inter-annual variability—much of which may be attributable to variation in recruitment. I collected plankton samples nightly during maximum flood tide in the York River, Virginia, July through November 1987, 1988, and 1989 to quantify variation in abundance of immigrating blue crab megalopae. The abundance of megalopae was highly episodic and positively related to wind stress to the west (1987, 1988, 1989), wind stress to the north (1987, 1989), observed tidal range in the York River at Gloucester Point (1987, 1988), and salinity at Gloucester Point (1988). Megalopal abundance was not correlated with current speed, water temperature, or Chesapeake Bay subtidal volume. Local wind forcing and tidal transport both appear to be important in transporting megalopae into lower Chesapeake Bay and the York River. Once inside the estuary, megalopae continue up-estuary transit via tidally-related vertical migration. While the occurrence of wind events is probably not necessary for some recruitment to occur, the number and timing of wind events (particularly “northeasters”) that significantly enhance ingress of megalopae may be a major determinant of inter-annual variability in blue crab recruitment.