MEPS 631:49-66 (2019)  -  DOI: https://doi.org/10.3354/meps13161

ABSTRACT: Predicting effects of environmental variations on species distributions requires knowledge of the trophic niches of potential competitors. We used gut contents, stable isotopes (SIs), and fatty acid (FA) biomarkers to investigate the feeding niches of 2 macrobenthic carnivore groups in the Bering Sea: the sea stars Leptasterias groenlandica and L. polaris and the whelks Neptunea heros and N. communis. Sea star guts contained no identifiable items, probably because of external digestion; gut contents were similar between whelk species. SI analyses reflect longer-term diets but require trophic discrimination factors (TDFs) between source and consumer tissues. TDFs are not available for sea stars or whelks, so we present a method for estimating TDFs. Isotopic niche diagrams differed among areas, with either inclusion of the niche of seas stars within the broader niche of whelks—about 40% overlap with similar niche breadth—or complete partitioning with a much broader niche for whelks. Analyzing FAs requires calibration coefficients (CCs) for differential assimilation into consumer tissues, but these coefficients are largely unknown for invertebrates. Moreover, cannibalism or consumption of phylogenetically related prey may confound diet estimates if FAs in carnivores are inherently more similar to those of related prey. Perhaps because of these issues, mixing models for FAs indicated different diets than indicated by SI analyses. Measurements of CCs and TDFs for a broader range of taxa are needed for applying these methods to diverse benthic consumers. Our results indicate that sea stars and whelks have diverse and overlapping diets that change with prey availability.

KEY WORDS: Calibration coefficients · Trophic discrimination factors · Echinoderm · Mollusk · Diet · Sea star · Gastropod · Whelk