Title

Global Comparison of Trophic Positions of Mesopelagic Myctophids and Stomiids Using Amino Acid Nitrogen Isotopic Analyses

Event Name/Location

Ocean Sciences Meeting, Salt Lake City, Utah, February 20-24, 2012

Document Type

Conference Proceeding

Publication Date

2-23-2012

Abstract

We examined the biogeochemical and ecological mechanisms responsible for variability in bulk and amino acid (AA) stable nitrogen isotope compositions in two important mesopelagic fish families, Myctophidae and Stomiidae, from five globally distributed regions. Using the δ15N values of individual AAs we quantified trophic positions (TPs) of these fishes. Despite variability in bulk tissue δ15N values, TPs are nearly uniform within both families of fishes across all regions. Differences in the bulk and AA δ15N values reflect region-specific water mass biogeochemistry controlling δ15N values at the base of the food web and these differences are inherited by the fishes analyzed. TPs calculated from AA isotopic analyses for myctophids (TP ~2.9) approximate expectations from stomach content (SC) studies describing these fishes as zooplanktivorous (TP ~3.2). In contrast, TPs calculated from AA analyses for stomiids (TP ~3.2) were lower than expected given previous SC studies, which report that stomiids are piscivorous (TP~4.1) across all regions. Our TP estimates suggest that stomiids are more similar to myctophids and are not strict piscivores, calling for possible reevaluation of the trophic roles of these fishes.