Habitat use patterns and edge effects across a seagrass-unvegetated ecotone depend on species-specific behaviors and sampling methods

ABSTRACT: Although habitat edges can be areas of elevated richness and intense ecological interactions, results from studies of mesopredators in seagrass ecosystems are equivocal, with some communities sensitive to the mere presence of seagrass, while others respond specifically to edges and landscape structure. We attempted to address these discrepancies through a species-specific lens, investigating patterns in aggregate and per-taxon mesopredator densities and behaviors across a seagrass-unvegetated ecotone at 3 sites in Washington State, USA, with special focus on patterns apparent on edges. Aggregate abundance was enhanced inside eelgrass (in seines) and on edges (in videos) relative to unvegetated habitats, a difference attributed to the abilities of the 2 methods to sample dominant taxa in different habitats. Both methods concurred that structure-association primarily occurred for pelagic, not benthic taxa. Videos suggested that shiner perch and stickleback moved more slowly in eelgrass interiors relative to unvegetated habitat, that stickleback fed more frequently in interior habitat, and that habitat use did not differ between low and high water. Eelgrass appears to disproportionately benefit small pelagic taxa rather than benthic species, but no distinct responses to edges were detected for the distribution or behavior of dominant taxa. Overall, responses to structure were taxon-specific, and for most taxa, shoot structure seemed more important than landscape structure for distribution and behavior. Our results suggest that the wide variation in community responses to landscape structure found in the literature may result from differences in local species pools, and the ability of sampling gear to detect specific taxa in different habitats.