Continental Shelf Research 19 (1999) 1171}1198 Larval "sh assemblages and water mass history in a major faunal transition zone Thomas M. Grothues*, Robert K. Cowen Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000, USA Received 9 June 1998; received in revised form 4 January 1999; accepted 6 January 1999 Abstract 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 "sh transport via these features could have implications to "sh population genetics, year- class structure, zoogeography, and access to nursery habitat. As a step in the examina- tion of larval exchange between the MAB and SAB, we studied the association of spring larval "sh 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 in#uenced by oceanographic conditions. Net assemblages from mixed waters were do- minated by taxa with widespread adult distributions (e. g. Peprilus triacanthus, synodon- tidae, 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 "delity to environ- mental indicators, thereby allowing for insight into the nature of the apparent di!erential permeability of this boundary zone to various species and into the precision of future * Corresponding author. Tel.: #001-516-632-8701; fax: 001-516-632-8220. E-mail address: grothues@msrc.sunysb.edu (T.M. Grothues)  Present address: Marine Biology and Fisheries, Rosenteil School of Marine and Atmospheric Sciences, 4600 Rickenbacker Causeway, Miami, FL 33149-1098, USA. 0278-4343/99/$ - see front matter  1999 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 8 - 4 3 4 3 ( 9 9 ) 0 0 0 1 0 - 2