Further support for the hypothesis that internal waves can cause shoreward transport of larval invertebrates and fish

In areas of mesotides (tidal range 2 to 4 m) and narrow continental shelves (~30 km) internal waves can transport (Le., convey from one place to another) the larvae of coastal organisms shoreward. Research reported here was in an area of microtides (tidal range 80 km), the South Atlantic Bight. Half of the sampled sets of internal waves were aligned parallel to shore and probably originated at the shelf break. The higher densities oflarvae and flotsam in the slicks over these internal waves (convergence zones) than in the rippled water between slicks (divergence zones) indicates that these waves were transporting larvae and flotsam shoreward. All nontransporting internal waves were aligned at a sharp angle to shore and may have formed over shoals oriented perpendicular to shore. To further test the hypothesis that internal waves can transport larvae, surface plankton were col­ lected from the waters over, in front, and behind a set of internal waves. The density of PortulIU8 spp. megalopae was significantly higher in waters in front of the set than behind. The average densities of a variety of larval fish and invertebrates were significantly higher over the internal waves than in front of the set of waves. These data indicate that internal waves can cause shoreward transport of larvae and flotsam. Precompetent larval fish were not carried shoreward by this set of waves while competent stages (Le., juvenile through postflexion) were transported shoreward.