Trophic Structure of Mesopelagic and Bathypelagic Micronekton in Relation to Mesoscale Oceanographic Features in the Northern Gulf of Mexico

The Deepwater Horizon oil spill, which released hydrocarbons into the deep-pelagic environment of the Gulf of Mexico (GoM), revealed significant data gaps with respect to the Gulf’s largest habitat including a paucity of information regarding the trophic structure of meso- and bathypelagic food webs. Gaining a better understanding of trophic dynamics is important to understanding ecosystem functioning and can provide insight into ecosystem resiliency in the face of large-scale perturbations. Describing trophic structure of pelagic assemblages in the GoM is complicated by diel vertical migration of many species and the presence of mesoscale oceanographic features (loop current, anticyclonic, cyclonic eddies) which can persist for months and have been shown to affect food web structure in pelagic systems. To better understand the spatial and temporal dynamics of deep pelagic food webs in the GoM we used stable isotope analysis (δ13C & δ15N) to examine the trophic dynamics of particulate organic matter (POM) and meso- and bathypelagic micronekton in relation to mesoscale anticyclonic and cyclonic features in the GoM. At each sampling location POM samples were taken at four depths throughout the water column while micronekton samples were collected using a 10-m2 MOCNESS midwater trawl sampling specific stratified depths from the surface to 1500 m. POM samples were found to be enriched in 15N with increasing depth regardless of feature type which was reflected in the δ15N of consumers. Deeper dwelling non-migratory species were enriched in 15N compared to migratory taxa despite known dietary and trophic similarities suggesting an increased reliance on deep suspended carbon sources by non-migratory species. By describing vertical and horizontal patterns in trophic structure of deep pelagic micronekton this project will provide baseline trophic data that can be used to inform spatially explicit ecosystem models and will provide insight into the structure and functioning of the northern GoM pelagic ecosystem