TEMPORAL AND VERTICAL-DISTRIBUTION OF CRAB LARVAE IN A TIDAL PASS

We investigated the vertical and temporal distributions of portunid zo ea and Callinectes megalopae in a tidal pass of the Texas coast. Zoea were equally abundant on ebb and flood tide but were more abundant dur ing the day than at night. Megalopae were more abundant during flood t ide and at night than during ebb tide or during the day. We examined t he evidence for selective tidal stream transport in both life-history stages. Depth of the centers of mass of the larval distributions and t he dispersions around those centers were unrelated to temperature, sal inity, current velocity, and time of day. Scaling arguments suggest th at the absence of pattern in the vertical distributions was not due to turbulent mixing. There was little evidence that either larval stage used these environmental characteristics as cues for changes in behavi our. However, the presence of megalopae in the water column primarily during flood tide does support the tidal transport hypothesis. Megalop ae may have difficulty sensing and reacting to environmental cues in w ell mixed estuaries with semidiurnal tides.