Award: OCE-1635716

We examined the role of sea otters (Enhydra lutris), as apex predators, on trophic interactions and community function within seagrass systems using observational and experimental research approaches. The loss of apex predators can result in ecological phase shifts, through alteration of communities, ecosystem function, and resilience, globally. Our research was based in Southeast Alaska where sea otters are recolonizing and exist along gradients of time occupied and density. We examined the top-down and bottom-up effects on the trophic structure between sea otters and seagrass by measuring the responses of organisms at each trophic level, including mesopredators, mesograzers, and interactions with associated algal populations (i.e. macroalgae and epiphytes). We did not find evidence for a top-down trophic cascade of sea otters across these different trophic levels, as was observed in California. Instead, we found direct positive and negative effects of sea otters on seagrass via active foraging for clams (bioturbation). We found seagrass bed expansion and carbon sequestration in soft-sediment habitats in the presence of sea otters. Yet, the highest densities of sea otters resulted in extensive disturbance that removed seagrass from much of the intertidal zone. Our research has local and broad scientific significance because of the local and global value of apex predators and the ecological contributions of these apex predators and seagrass to ecosystem services. We communicated our results broadly, and engaged undergraduate, graduate students, postdoctoral researchers, and a large number of volunteers. Last Modified: 06/15/2021 Submitted by: Ginny L Eckert