Elevated meroplankton abundance in surface slicks during internal wave forcing at three coastal sites in Mexico

The supply of meroplanktonic larvae to coastal habitats by physical transport mechanisms is important for the persistence of benthic marine invertebrate populations. Larvae can accumulate in convergent bands that are often visible as smooth surface slicks in areas where surfactants reduce capillary waves. Slicks can form above passing troughs of internal waves, which occur on most coasts during stratified periods. In this study, during periods of strong internal wave forcing under spring tide conditions in three bays along the Mexican coastline, we sampled high-frequency (f ≥ 1 cycle h -1 ) changes in the abundance of marine meroplankton. Concurrently, we recorded visual observations of surface slicks and measured physical conditions in the water column (i.e., temperature and currents). Surface slicks were observed at all three sites, with over 70% occurring at times theoretically predicted from current flows. The slick periods showed warmer temperatures or lower strain values, suggesting slicks may be associated with warm convergence zones. Chthamaloid cyprids and mussel veligers were the dominant meroplankton found, with their abundance being significantly greater (2–6 times) within slicks at all sites and a significant positive relationship with temperature found at 2 of the 3 sites. These results support the hypothesis that plankton accumulation does occur in visible surface slicks. We propose that the slicks measured in this study were related to internal wave convergence zones, meriting further exploration as significant mechanisms of plankton accumulation. • •Slicks associated with internal waves occurred when predicted from current flows • •Slicks were warmer with lower strain suggesting internal wave convergent slicks • •Meroplankton abundances were much greater (2–6 times) within slicks • •Meroplankton abundances were significantly related to temperature and strain • •Meroplankton accumulation occurs in internal wave surface slicks at 3 different sites