Larval fish assemblages and water mass history in a major faunal transition zone

A region of distinct oceanographic features that result from the meeting of several water masses is marked by Cape Hatteras, North Carolina, between the Middle Atlantic Bight (MAB) and South Atlantic Bight (SAB). The features are dynamic, corresponding, in part, to the degree of water exchange between the MAB and SAB. The extent of larval fish transport via these features could have implications to fish population genetics, year-class structure, zoogeography, and access to nursery habitat. As a step in the examination of larval exchange between the MAB and SAB, we studied the association of spring larval fish assemblages with environmental variables descriptive of the water mass origins. The region was clearly an oceanographic and ichthyoplankton faunal transition zone. Larval distribution corresponded to patterns of adult distributions along the entire eastern seaboard. High taxa-environment correlations described a boundary assemblage strongly influenced by oceanographic conditions. Net assemblages from mixed waters were dominated by taxa with widespread adult distributions (e. g. Peprilus triacanthus, synodontidae, triglidae, clupiedae, others) rather than a mix of taxa from other groups. MAB water contained Limanda ferruginea and Benthosema glaciale in deep, cold water and Glyptocephalus cynoglossus, Hippoglossina oblonga, Scomber scombrus, Lophius americanus, and others in shallow, warmer, less saline water. High densities of numerous sub-tropical species, (e.g. Xyrichtys novacula, Bothus spp.) and low densities of many others were found in SAB waters but varied greatly in distribution with depth. Taxa varied in their fidelity to environmental indicators, thereby allowing for insight into the nature of the apparent differential permeability of this boundary zone to various species and into the precision of future predictions regarding transport related recruitment success.