Determination of sea star diet using gut content, stable isotope, and fatty acid analyses

Forecasting the impact of climate warming on ecological communities requires reliable quantitative information on species interactions, particularly trophic relationships.  In the Bering Sea changes in the timing and extent of sea ice cover as a result of increasing temperatures are expected to affect benthic food webs through changes in algal phenology, predator distribution, and predator abundance.  As part of a larger effort to develop a food web model for the northern Bering Sea benthic ecosystem we are analyzing the diets of a diverse group of predators.  Diet analysis of many benthic marine invertebrates using gut analysis is inadequate for a number of reasons, including loss of gut contents during specimen retrieval, extraoral feeding strategies, and differential digestion of ingested materials.  Trawl surveys performed during the spring of 2006 indicated that sea stars from the genus Leptasterias are abundant benthic predators (as much as 73% of epibenthic predators at some stations) in the northern Bering Sea.  Preliminary examination of sea star stomachs suggests that known prey items are underrepresented in gut contents.  To obtain accurate estimates of sea star and gastropod diets we are developing techniques based on the analysis of stable isotopes (¹³C and ¹⁵N) and fatty acids of prey and predator tissue to complement our gut content analyses.  The methods developed during this study should be broadly applicable to diet analysis of other marine invertebrates.