Connectivity of coastal and neritic fish larvae to the deep waters

Four ichthyoplankton cruises and backward tracking experiments were conducted to study the connectivity of coastal and neritic fish larvae over the continental slope and to the oceanic deep-water region of the western Gulf of Mexico. Distribution patterns of larval abundance at oceanic stations showed higher abundance and the presence of larvae at oceanic stations during two cruises. Larval transport was simulated using outputs of a data assimilation model that represented the flow conditions during each cruise. Higher abundances of larvae of coastal and neritic species at oceanic stations agreed with offshore transport inferred from numerical experiments seeding particles over different spatial scales (stations vs. transects). Satellite images of surface chlorophyll were consistent with the circulation patterns indicated by the model, indicating filaments of shelf waters were transported toward the transects with higher larval abundances. Particle tracking experiments indicated that the northwestern shelf provinces of Perdido, Tamaulipas, and Texas were the main source of propagules to the oceanic region, while shelf provinces of northern Veracruz, Campeche, Yucatan, Louisiana, and Mississippi-Alabama contributed much less. The length and intensity of the shelf front limited ichthyoplankton cross-shelf exchange during some cruises, and mesoscale anticyclonic and cyclonic eddies advected larvae to the deep-water region during others. The agreement between the spatial distribution of fish larvae and the simulated larval transport confirm that circulation models are a valuable tool for examining potential dispersal pathways of neritic species, as long as similar spatial and temporal scales as the ones used in this study are considered.