Preliminary assessment of the association of larval fishes with pelagic Sargassum habitat and convergence zones in the northcentral Gulf of Mexico

Surface plankton samples were taken adjacent to concentrations of pelagic Sargassum during May and July 2000 in the northcentral Gulf of Mexico. Sampling was conducted next to Sargassum located both along convergence zones (fronts) and in areas not associated with particular hydrographic features. In addition, collections were taken up to 1:5 kilometers away from the sampled Sargassum as a control. A total of 1453 larvae/postlarvae comprising 22 families were collected. Collections were dominated by carangids and exocoetids, but also included specimens of tuna (including bluefin in May), dolphin and billfishes. Species composition and abundance were generally similar for collections taken both adjacent to Sargassum located along frontal zones and "control" collections taken within a few hundred meters of the sampled front. These preliminary observations indicate the potential influence of both Sargassum habitat and the convergence of water masses associated with frontal zones. The supposition that the convergence of water masses affects the diversity and abundance of fish larvae is further strengthened by the relatively low diversity and abundance of larvae found in collections taken adjacent to large patches of Sargassum not associated with particular hydrographic features. Larvae may accumulate in frontal zones both with and without Sargassum, but the growth and survival of the larvae of many species may be quite different in both areas.