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MEPS prepress abstract   -  DOI:

Sea otter effects on trophic structure of seagrass communities in southeast Alaska

Wendel W. Raymond*, Julie B. Schram, Ginny L. Eckert, Aaron W. E. Galloway

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ABSTRACT: Previous research in southeast Alaska on the effects of sea otters (Enhydra lutris) in seagrass (Zostera marina) communities identified many but not all of the trophic relationships that were predicted by a sea otter mediated trophic cascade. To further resolve these trophic connections, we compared biomass, carbon (δ13C) and nitrogen (δ15N) stable isotope (SI), and fatty acid (FA) data from 16 taxa at three sites with high and three sites with low sea otter density (8.2 and 0.1 sea otters/km2 respectively). We found lower crab and clam biomass in the high sea otter region, but did not detect a difference in biomass of other seagrass community taxa or the overall community isotopic niche space between sea otter regions. Only staghorn sculpin differed in δ13C between regions, and Fucus, sugar kelp, butter clams, dock shrimp, and shiner perch differed in δ15N. FA analysis indicated multivariate dissimilarity in 11 of the 15 conspecifics between sea otter regions. FA analysis found essential FA, which consumers must obtain from their diet, including 20:5ω3 (EPA) and 22:6ω3 (DHA), were common in discriminating conspecifics between sea otter regions suggesting differences in consumer diets. Further FA analysis indicated that many consumers rely on diverse diets, regardless of sea otter region, potentially buffering these consumers from sea otter mediated changes to diet availability. While sea otters are major consumers in this system, further studies are needed to understand the mechanisms responsible for the differences in biomarkers between regions with and without sea otters.