Larval Fish Assemblages at the Loop Current Boundary in the Gulf of Mexico

As part of a Gulf-wide ichthyoplankton survey of the Gulf of Mexico in the spring of 1987, eight transects were made across the Loop Current boundary using bongo nets fished to 200 m depth and neuston nets fished at the surface. The boundary was determined by satellite images of the Loop Current and the ship was positioned to make a transect across the boundary whenever it approached a boundary during its normal survey operations. Eight transects were made and the composition and abundance of the fish larvae were determined for each tow. Eight to 10 ten tows were made at 2-to 4-km intervals. Taxonomic diversity of the ichthyoplankton was higher than previously reported for the Gulf of Mexico or Caribbean (100 families). Cluster analysis of families produced two major groups, oceanic and continental, but our hypothesized frontal assemblage is not coequal with the oceanic and shelf groups. Cluster analysis of stations also supported the hypothesis of contrasting oceanic and shelf assemblages. Principal-components analysis found more than one-half of the variance in the data to be summarized by three independent patterns. The high diversity of larval fishes is due to the mix of faunas from tropical and warm temperate oceanic, mesopelagic, and coastal demersal and pelagic species which is enhanced by the dynamics of the oceanographic system of the Loop Current.