Are Leptocephali Assemblages Confined By Oceanographic Features? – Investigating Distributional Patterns Across the Subtropical Convergence Zone of the Sargasso Sea

We examined species assemblages of leptocephali across part of the Subtropical Convergence Zone (STCZ) of the Sargasso Sea.  Three cross-frontal transects along the STCZ were sampled in spring 2007. About 20 species from nine families were collected at 8 stations. Four species were abundant, the two catadromous eels, Anguilla anguilla and A. rostrata, as well as the shelf species Ariosoma balearicum and the oceanic Nemichthys scolopaceus. While the two Anguillids and the Congrid, A. balearicum, exhibited substantially elevated abundances within the confines of the STCZ’s bordering frontal zones, the oceanic Nemichthid, N. scolopaceus showed somewhat less dichotomous cross-frontal abundances.  The leptocephali-abundance patterns were inversely-mirrored in species assemblages of several common non-leptocephali fish larvae, indicating structuring of larval fish assemblages on small geographic scales. Further studies will emphasize the physical and biological background of such structuring, as well as investigate assemblage changes across larger geographic scales.