Mr. Roman et Wc. Boicourt, Dispersion and recruitment of crab larvae in the chesapeake bay plume: Physical and biological controls, ESTUARIES, 22(3A), 1999, pp. 563-574
As part of the Microbial Exchanges and Coupling in Coastal Atlantic Systems
(MECCAS) Project, crab larvae were collected in the shelf waters off Chesa
peake Bay in June and August 1985 and April 1986. We conducted hydrographic
(temperature, salinity, nutrients) and biological (chlorophyll, copepods)
mapping in conjunction viith Eulerian and Lagrangian time studies of the ve
rtical distribution of crab larvae in the Chesapeake Bay plume. These abund
ance estimates are used with current meter records and drifter trajectories
to infer mechanisms of larval crab dispersion to the shelf waters and recr
uitment back into Chesapeake Bay. The highest numbers of crab larvae were u
sually associated with the Chesapeake Bay plume, suggesting that it was the
dominant source of crab larvae to shelf waters. Patches of crab larvae als
o were found in the higher salinity shelf waters,:and possibly were remnant
s of previous plume discharge events. The distribution of crab larvae in th
e shelf waters changed on 1-2 d time scales as a consequence of both variat
ions in the discharge rate of the Chesapeake Bay plume and local wind-drive
n currents. Downwelling;favorable winds (NW) intensified the coastal jet an
d confined the plume and crab larvae along the coast. In April during a dow
nwelling event (when northwesterly winds predominated), crab zoeae were tra
nsported southward along the coast at speeds that at times exceeded 168 km
d(-1). During June and August the upwelling-favorable Hinds (S, SW) opposed
the anticyclonic turn of the plume and, via Ekman circulation, forced the
plume and crab larvae to spread seaward. Plume velocities during these cond
itions generally were less,than 48 km d(-1). The recruitment of crab larvae
to Chesapeake Bay is facilitated in late summer by the dominance of southe
rly winds, which can reverse the southward flow of shelf waters. Periodic d
ownwelling-favorable winds can result in surface waters and crab larvae mov
ing toward the entrance of Chesapeake Bay. Approximately 27% of the larval
crabs spend at least part of the day in bottom waters, which have a residua
l drift toward the bay mouth. There appears to be a variety of physical tra
nsport mechanisms that can enhance the recruitment of crab larvae into Ches
apeake Bay.