Transport of crab larval patches in the coastal ocean

We assessed the role of wind and buoyancy forcing on the transport of newly hatched blue crab larvae Callinectes sapidus near the mouth of Delaware Ba y, USA, Eight patches of larvae were tagged with satellite-tracked drifters and followed for periods of 1 to 11 d. We conducted daily plankton tows wi thin a 3.2 km(2) area circumscribing each drifter. This allowed us to verif y that each drifter remained within a patch, Trajectories of the patches we re assessed in relation to physical data (salinity, temperature, winds, and river discharge) and compared to trajectories predicted by a 2-dimensional mathematical model. Analysis of CTD data indicated that 3 patches were-ini tially tagged in the coastal plume emanating from Delaware Bay, while 5 pat ches were initially tagged in shelf water adjacent to the plume. Patches oc curring in plume waters traveled farther down-shelf (southward) than those in adjacent shelf waters. Winds modified this along-shelf transport. Specif ically, upwelling-favorable (northward) winds mixed larvae offshore and out of the coastal plume. Downwelling-favorable (southward) winds drove patche s of larvae across the continental shelf and toward the coast. Trajectories were simulated well by the mathematical model. As river discharge diminish ed in the late summer, the effect of winds (relative to buoyancy forcing) o n larval transport increased. This shift in the dominant forcing mechanism was demonstrated both by the trajectories of the tagged larval patches and by predictions from the mathematical model.