Distribution of crab larvae in relation to tidal fronts in Delaware Bay, USA

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Abstract
Replicate observations of hydrographic structure and crab larval distributions were conducted at ebb-tide, flood-tide and non-frontal sites in lower Delaware Bay. Results show that frontal structure is restricted to the upper 2 m of the water column and that convergent velocities associated with the fronts are sufficient to collect buoyant and upward-swimming plankton at the surface. Despite this, maximum concentrations of larvae at fronts were found at depths greater than the frontal pycnocline, while larvae at the non-frontal site showed no significant difference in their abundance with depth. While the observed frontal distributions may be due to a balance between upward swimming by the larvae and downward movement of water at the frontline, ecological effects are mitigrated by the ephemeral nature of the fronts.