Larval fish assemblages of myctophids in the deep water region of the southern Gulf of Mexico linked to oceanographic conditions

In the Gulf of Mexico, the distribution of larval fish assemblages have been linked to continental shelf vs oceanic habitats and mesoscale structures such as cyclonic and anticyclonic eddies. Myctophids have a worldwide distribution and are one of the mesopelagic fish families with higher biomass, thus playing a key role in the trophic structure of oceanic communities. However, studies focused on their larval ecology and distribution within the gulf are limited. This study evaluated whether the formation of myctophid larval assemblages can be linked to local adult population spawning patterns and/or oceanographic conditions and surface transport. Ichthyoplankton samples were collected in August–September 2015 using standard bongo net tows. Stations extended throughout Mexico's Exclusive Economic Zone (19°N–25°N) deep water region, including the Yucatan Channel. Myctophid comprised 24.6% of the standardized total larval abundance and were present at all stations. Two dominant assemblages (out of six identified with a Bray–Curtis dissimilarity analysis) were found in stations of the central gulf and the Bay of Campeche. The high proportion of preflexion larvae coupled with differences in hydrographic parameters and surface circulation between the central gulf and the Bay of Campeche, indicated that local adult fish populations and their spawning patterns likely contribute more to the formation of these assemblages than oceanographic conditions and surface transport. Stations from the northern Yucatan Peninsula located within the region of influence of the Loop Current shared a common assemblage, which may reflect biogeographic differences in the myctophid species composition between the northern Caribbean and western gulf. These results highlight the importance of adult distribution and local spawning, providing insight into biogeographic patterns during the early life stages of mesopelagic fishes in the Gulf of Mexico.