Dietary connections of marine species to kelp and eelgrass

Abstract Ecosystem-based fisheries management requires an understanding of the interactions between managed and unmanaged species and the connections they have with their habitats. Although aquatic plants are known to provide important shelter for a variety of species, an often-overlooked component is the extent to which primary producers contribute to their diet. In this study, we reconstructed the dietary connections between 18 consumers, including vulnerable rockfish species, and several primary producers. Two of these primary producers, Zostera marina (eelgrass) and Nereocystis luetkeana (bull kelp), have experienced spatial variation in abundance and substantial declines, respectively, within Puget Sound, Washington, USA. Using stable isotope ratio data, we estimated that both bull kelp and Smithora naiadum (an epiphytic algae) were the most important sources of carbon in consumer diets, followed by particulate organic matter and eelgrass. Our results indicated strong dietary connections for certain consumers, such that epiphytic algae was found to comprise greater than 40% of the diets of copper rockfish ( Sebastes caurinus ), while bull kelp contributed most to the diets of Pacific staghorn sculpin ( Leptocottus armatus ) and quillback rockfish ( S. maliger ). For several consumers, we observed habitat-mediated prey choice because the relative importance of bull kelp or epiphytic algae in their diets increased when these consumers were collected from sites dominated by kelp or eelgrass, respectively. Understanding the strength of these trophic relationships is an important step for predicting ecosystem consequences following perturbations within these habitats, and such information is vital to managers making decisions related to the conservation of valuable populations.