Trophic Diversity of a Mesopelagic Fish Community

To understand the character of prey partioning in a low latitude oligotrophic region, a composite picture of the trophic structure of a mesopelagic fish community was made from the eastern Gulf of Mexico. Two hundred and twenty three species were collected in the area of which l6l species were abundant enough for analyses. Fifteen major categories of prey biomass are identified for diet analyses: viz. copepods, ostracods, amphipods, euphausiids, decapods, larvaceans, salps, coelenterates (primarily siphonophores), unidentified gelatinous prey, polychaetes, gastropods, cephalopods, chaetognaths, fish, other food. Prey partitioning is minimal across major prey categories as the vast majority of mesopelagic fishes are primarily either copepod or fish predators. Those fishes utilizing other prey groups to a significant degree are either few in number and/or rare in abundance. Decapods are numerous in the area and the apparent lack of decapod predators might be caused by inadequate sampling of the larger oceanic fauna. To address the question of the influence of trophic relationships on the structure and maintenance of oceanic communities we need to know the predation impact of other faunal groups (e.g., coelenterates) besides that of the mesopelagic fishes