Cross-shelf distribution patterns of ichthyoplankton in La Parguera Bay and adjacent oceanic waters, southwest coast of Puerto Rico

The horizontal and vertical abundance patterns and taxonomic structure of larval fishes were examined across a neritic-oceanic gradient off La Parguera southwest coast of Puerto Rico. A total of 35,024 larval fishes, representing 82 families were collected. Total larval fish abundance declined across the neritic-oceanic gradient in each of the three cruises. Coral reef fish larvae were the numerically dominant assemblage as far as 29 km offshore but declined markedly to very low abundance at 46 km where oceanic type larvae prevailed. The horizontal distribution pattern of coral reef type larvae is taxon specific. Three basic dispersion patterns of Caribbean coral reef fish larvae can be discerned from this study, one mostly neritic (e.g. Clupeiformes), a widespread oceanic (e.g. Labridae) and one associated with the outer shelf and the shelf-edge (e.g. Lutjanidae).; The vertical distribution of fish larvae were described from samples collected in vertically stratified, step-oblique tows at three discrete depths within the surface mixed layer (surf 0–20, mid 21–40 and deep 41–60 meters). Water density profiles in February and May showed permanent stratification with well developed pycnoclines associated with increasing salinity and a decline of water temperature with depth. Pre-flexion coral reef fish larvae did not show any statistically significant pattern of abundance in their vertical distribution within the surface mixed layer. Only a few families at post-flexion stage showed statistically significant differences of abundance between depths, or between day and night samplings. Abundance of oceanic type larvae, such as myctophids, gonostomatids and photichtyids increased with depth, as well as coral reef fish larvae of the Gobiidae and Scaridae families. Conversely, Clupeiformes, Pomacentridae, Haemulidae and Holocentridae were more abundant at shallower depths within the surface mixed layer. Lutjanidae were found mostly in mid water.