Abstract

A major goal of ecological research is the ability to model food web dynamics so that predictions regarding changes in food web and ecosystem structure can be made. Before accurate models can be constructed, information pertaining to trophic relationships among functional groups, including estimates of trophic position using both stomach content analysis (SCA) and stable isotope analysis (SIA)are needed. Currently, several data sets utilizing SCA to describe trophic structure of micronketon (2-10 cm) in the deep-pelagic Gulf of Mexico (GoM) exist but studies using SIA are less common. Using a dataset including 58 species, we describe the trophic structure of deep- pelagic micronekton assemblages in the GoM using δ13C and δ15N using. Both vertically migrating, and non- migrating taxa representing a range of feeding modes, depth distributions, and putative trophic levels were selected to describe trophic variability within deep-pelagic assemblages. Additionally, samples of particulate organic matter (POM) from the epi-, meso-, and bathypelagic were used to delineate carbon source isotopic signatures. Isotopic signatures of POM samples were significantly different across depth zones displaying a pattern of enrichment in 15N with increasing depth. The δ13C values of micronekton varied among species, ranging from -22.73‰ to - 16.35‰ suggesting consumers utilize POM throughout the water column. Micronekton δ15N values ranged from 1.85‰ to 10.97‰ encompassing ~3 trophic levels. Elevated δ15N values in many non-migratory taxa suggest an increased reliance on deep-suspended POM when compared to migratory taxa who receive the bulk of their carbon from epipelagic sources. This project provides data that can be used to inform ecosystem models and will provide insight into the structure of the GOM’s deep-pelagic ecosystem.

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