Trophic niche partitioning of three larval Sciaenidae species in the north-western Gulf of Mexico

The ability of larval fish to find prey items in sufficient quantities plays an important role in determining survivorship. To understand trophic niche partitioning and the potential for competition, we analyzed morphology and digestive tract content in larvae of three co-occurring, sciaenid fish species: Cynoscion nothus, Larimus fasciatus and Micropogonias undulatus. Larvae were collected in the north-western Gulf of Mexico off Galveston, TX, at seven stations in October/November 2017. Intra- and interspecific diet composition was analyzed between three ontogenetic development stages and two sampling zones (nearshore vs mid-shelf). M. undulatus had a significantly smaller mouth size than the other two species and consumed smaller prey items compared with C. nothus. Copepoda dominated all larval diets. The highly abundant M. undulatus primarily ate Calanoida following typical Sciaenidae feeding preferences. The less abundant C. nothus and L. fasciatus shared Cyclopoida as a primary diet item but differed in the consumption of less important prey taxa (i.e. Ostracoda, Chaetognatha). Ontogenetic dietary shifts (ODSs) were observed for all species, with the timing and number of ODS differing for C. nothus between sampling zones. The inclusion of alternative food sources such as Cyclopoida and non-copepod prey taxa likely alleviated potential interspecific competition allowing for larval co-occurrence.