Partitioning of food resources in bathypelagic micronekton in the eastern Gulf of Mexico

Abstract

A mid-water trawl survey conducted between depths of 1000 and 3000 m in the eastern Gulf of Mexico found 54% of the organisms collected were gonostomatid fishes. Lophogastrids within the family Eucopiidae were also common (17.3%), as were decapod shrimps within the families Oplophoridae and Benthesicymidae (9.9 and 7.1% respectively). We examined the gut contents of 14 prominent species from this assemblage to determine if available food resources were partitioned. Cluster analysis of stomach contents resulted in 4 clusters based on taxonomic composition and 3 based on prey size. Bristlemouth fishes (Gonostomatidae) of the genus Cyclothone and lophogastrids of the genus Eucopia were planktivorous, consuming smaller prey items such as copepods and ostra- cods. Decapods within the family Oplophoridae tended to be piscivorous and consumed relatively large prey. Dendrobranchiate shrimps appeared to regularly consume detrital material, although the contribution of such material to the overall diet could not be quantified. The hatchetfish Sternoptyx pseudobscura had a large proportion of shallow-living taxa in its diet despite being non-migratory. Many of the bathypelagic species were found to be more piscivorous than mesopelagic counterparts within the same family or genus. Dietary overlap in both prey size and taxonomic composition was rare, occurring only 16.5% of the time. The most prevalent pattern (~50% of species pairings) was overlap in neither diet category, suggesting the species partitioned food resources.