Springtime ichthyoplankton of the slope region off the north-eastern United States of America: larval assemblages, relation to hydrography and implications for larval transport

Larval transport in the slope region off north-eastern North America influe nces recruitment to juvenile habitats for a variety of fishes that inhabit the continental shelf. In this study, collections of larval fishes were mad e during springtime over the continental slope to provide insights into lar val distributions and transport. Ichthyoplankton composition and distributi on mirrored the physical complexity of the region. Three larval fish assemb lages were defined, each with different water mass distributions. A Gulf St ream assemblage was found predominantly in the Gulf Stream and associated w ith filaments of discharged Gulf Stream water in the Slope Sea. Larvae of t his assemblage originated from oceanic and shelf regions south of Cape Hatt eras. Several members of this assemblage utilize habitats in the Middle Atl antic Bight (MAB) as juveniles (Pomatomus saltatrix, Peprilus triacanthus) and other members of the assemblage may share this life cycle (Mugil curema , Sphyraena borealis, Urophycis regia). A Slope Sea assemblage was found in all water masses, and was composed of epi- and mesopelagic fish larvae, as well as larvae of benthic shelf/slope residents. Larvae of one member of t his assemblage (U. tenuis) are spawned in the Slope Sea but cross the shelf -slope front and use nearshore habitats for juvenile nurseries. A MAB shelf assemblage was found in MAB shelf water and was composed of larvae that we re spawned on the shelf. Some of these species may cross into the Slope Sea before returning to MAB shelf habitats (e.g. Enchelyopus cimbrius, Glyptoc ephalus cynoglossus). Previous studies have examined the effect of warm-cor e rings on larval distributions, but this study identifies the importance o f smaller-scale features of the MAB shelf/slope front and of filaments asso ciated with Gulf Stream meanders. In combination with these advective proce sses, the dynamic nature of larval distributions in the Slope Sea appears t o be influenced, to varying degrees, by both vertical and horizontal behavi our of larvae and pelagic juveniles themselves.