title: Trophic cascades on the edge: fostering seagrass resilience via a novel pathway.
abstract: Despite widespread degradation, some coastal ecosystems display remarkable resilience. For seagrasses, a century-old paradigm has implicated macroalgal blooms stimulated by anthropogenic nutrient, loading as a primary driver of seagrass decline, yet relatively little attention has been given to drivers of seagrass resilience. In Elkhorn Slough, CA, an estuarine system characterized by extreme anthropogenic nutrient loading and macroalgal (Ulva spp.) blooms, seagrass (Zostera marina) beds have recovered concurrent with colonization of the estuary by top predators, sea otters (Enhydra lutris). Here, we follow up on the results of a previous experiment at the seagrass interior, showing how sea otters can generate a trophic cascade that promotes seagrass. We conducted an experiment and constructed structural equation models to determine how sea otters, through a trophic cascade, might affect the edge of seagrass beds where expansion occurs. We found that at the edge, sea otters promoted both seagrass and ephemeral macroalgae, with the latter contributing beneficial grazers to the seagrass. The surprising results that sea otters promote two potentially competing vegetation types, and a grazer assemblage at their boundary provides a mechanism by which seagrasses can expand in eutrophic environments, and contributes to a growing body of literature demonstrating that ephemeral macroalgae are not always negatively associated with seagrass. Our results highlight the potential for top predator recovery to enhance ecosystem resilience to anthropogenic alterations through several cascading mechanisms.
authors.affiliation: Division of Marine Science and Conservation, Nicholas School of the Environment, Duke University, Beaufort, NC, 28516, USA. bbhughes@ucsc.edu.|Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 100 Shaffer Rd., Santa Cruz, CA, 95060, USA. bbhughes@ucsc.edu.|Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Rd., Watsonville, CA, 95076, USA. bbhughes@ucsc.edu.
authors.forename: Brent B
authors.initials: BB
authors.lastname: Hughes
authors.affiliation: Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA.|Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Rd., Watsonville, CA, 95076, USA.
authors.forename: Kamille K
authors.initials: KK
authors.lastname: Hammerstrom
authors.affiliation: Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA.|Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Rd., Watsonville, CA, 95076, USA.
authors.forename: Nora E
authors.initials: NE
authors.lastname: Grant
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 100 Shaffer Rd., Santa Cruz, CA, 95060, USA.|Moss Landing Marine Laboratories, 8272 Moss Landing Rd., Moss Landing, CA, 95039, USA.|Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Rd., Watsonville, CA, 95076, USA.
authors.forename: Umi
authors.initials: U
authors.lastname: Hoshijima
authors.affiliation: Department of Ecology Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, 93106, USA.|Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Rd., Watsonville, CA, 95076, USA.
authors.forename: Ron
authors.initials: R
authors.lastname: Eby
authors.affiliation: Department of Ecology and Evolutionary Biology, University of California Santa Cruz, 100 Shaffer Rd., Santa Cruz, CA, 95060, USA.|Department of Ecology Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, 93106, USA.|Elkhorn Slough National Estuarine Research Reserve, 1700 Elkhorn Rd., Watsonville, CA, 95076, USA.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Wasson
mesh_terms: D000818:Animals; D017753:Ecosystem; D063366:Estuaries; D010041:Otters; D012624:Seaweed; D035962:Zosteraceae
keywords: Ecosystem recovery; Eutrophication; Food web; Predator recovery; Trophic dynamics