Feeding Ecology of Deep-Pelagic Fish Larvae in the Northern Gulf of Mexico

The deep-pelagic environment encompasses ocean waters below 200 m depth, and comprises 90% of the volume of the Gulf of Mexico. Deep-pelagic fishes are important prey for many oceanic consumers, but relatively little is known about their early life history, including larval fish trophic ecology. Understanding the role of deep-pelagic fish larvae in oceanic food webs is important in the development of ecosystem models that examine the connectivity (via vertical migrations) between the deep-pelagic and epipelagic environments with respect to trophic interactions, nutrient cycling, and carbontransfer. In this study, archived plankton samples collected during 2010 and 2011 were used to describe the trophic ecology of the dominant deep-pelagic fish larvae collected in the northern Gulf of Mexico. Bulk-tissue stable isotope analysis of δ¹³C and δ ¹⁵N values were performed on larvae from four families: Myctophidae (Lanternfishes), Gonostomatidae (Bristlemouths), Sternoptychidae (Hatchetfishes) and Phosichthyidae (Lightfishes). Gut contents were counted and identified to provide taxon-specific diet information. Gut fullness indices were assigned to each larva and compared across ontogenetic stages, sizes, sampling depths, and time of collection. In addition, compound-specific stable isotope analysis of amino acids of nitrogen was performed on a subset of samples from the Family Paralepididae (Barracudinas) to differentiate between true ontogenetic shifts in diet and isotopic shifts related to water depth. Gut content analysis revealed a high level of gut emptiness, however preliminary analyses suggest that variability in gut fullness was driven more by ontogenetic stage and size than by time of day or depth of capture. Preliminary analysis of isotopic data using Bayesian standard ellipses revealed that isotopic niche areas varied among six myctophid genera, with Lampanyctus spp. having the broadest niche area and Ceratoscopelus spp. having the narrowest.