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 3 sites with high and 3 sites with low sea otter density (8.2 and 0.1 sea otters km^-2, 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 FAs, 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.

中文翻译：

---

海獭对阿拉斯加东南部海草群落营养结构的影响

摘要：先前在阿拉斯加东南部对海草Zostera 码头群落中海獭Enhydra lutris影响的研究确定了许多但不是所有的营养关系，这些关系是由海獭介导的营养级联预测的。为了进一步解决这些营养联系，我们比较了来自 3 个高位点和 3 个低位点的 16 个分类群的生物量、碳 (δ ¹³ C) 和氮 (δ ¹⁵ N) 稳定同位素 (SI) 和脂肪酸 (FA) 数据。海獭密度（8.2 和 0.1 海獭公里^-2， 分别）。我们发现公海獭地区的螃蟹和蛤生物量较低，但没有检测到其他海草群落类群的生物量或海獭地区之间的整体群落同位素生态位空间的差异。只有鹿角杜鹃在不同地区的δ ¹³ C 存在差异，而墨角藻、糖海带、奶油蛤、码头虾和鲢鱼的 δ ¹⁵存在差异N. FA 分析表明海獭区域之间 15 个同种物种中的 11 个存在多元差异。FA 分析发现，消费者必须从他们的饮食中获得必需的 FA，包括 20:5ω3 (EPA) 和 22:6ω3 (DHA)，在区分海獭区域之间的同种中很常见，这表明消费者饮食存在差异。进一步的 FA 分析表明，许多消费者依赖于多样化的饮食，无论海獭产区如何，这可能会缓冲这些消费者免受海獭介导的饮食供应变化的影响。虽然海獭是该系统的主要消费者，但需要进一步研究以了解导致有海獭和没有海獭的地区之间生物标志物差异的机制。