Epibenthic Predators Control Mobile Macrofauna Associated with a Foundation Species in a Subarctic Subtidal Community

Foundation species (FS) are strong facilitators providing habitat for numerous dependent organisms. The communities shaped by FS are commonly structured by interplay of facilitation and consumer control. Predators or grazers often indirectly determine community structure eliminating either FS or their principal competitors. Alternatively, they can prey on the dependent taxa directly, which is generally buffered by FS via forming complex habitats with numerous refuges. The latter case has been never investigated at high latitudes, where consumer control is widely considered weak. We manipulated the presence of common epibenthic crustacean predators to assess their effect on mobile macrofauna of the clusters developed by a FS (barnacle and its empty tests) in the White Sea shallow subtidal (65° N). While predation pressure on the FS itself here is low, the direct effects of a spider crab and a shrimp on the associated assemblages were unexpectedly strong. Removing the predators did not change species diversity, but tripled total abundance and altered multivariate community structure specifically increasing the numbers of amphipods, isopods (only affected by shrimp), and bivalves. Consumer control in the communities shaped by FS may not strictly follow the latitudinal predation gradient rule.