Effects of wind-generated coastal currents on the transport of blue crab megalopae on a shallow continental shelf

We explore the role of wind-generated coastal circulation regimes on the transport of blue crab megalopae. While this role is examined in the light of past observations and model simulations on the continental shelf of the southeast U.S., the physical principles have general applicability to other coastal regions with broad shallow continental shelves. An examination of three years of blue crab settlement data reveal that major settling events occurred during upwelling, downwelling and calm winds. There was no correlation with spring tides. Shoreward advecting currents occur in both upwelling and downwelling circulation regimes, but their location in the water column differs. Moreover, the configuration of the coastal frontal zone can change after downwelling ceases and produce shoreward advection in the lower portions of the water column. Thus, shoreward advection of megalopae (and other larvae) depends on vertical position in the water column, a position sensitive to behavior and vertical mixing. Many scientists have sought correlations between factors associated with recruitment and physical parameters. This approach has obvious advantages as long as the physical model from which the parameters are derived is based on a precise assumptions about how the physical model works. Our work suggests that we must have equally precise assumptions for vertical migratory behavior before we can demonstrate that this correlative approach produces consistent results.