Impacts of habitat and predation on epifaunal communities from seagrass beds and artificial structures.

Within the coastal marine environment, the increased presence of artificial habitat can have negative impacts on the functioning of marine communities. Artificial structures provide a novel, hard surface for the colonization and growth of a variety of marine species and disproportionally favor introduced species. With the global rise in hardened shorelines, it is imperative to examine the ecological processes that occur within these habitats to those occurring in natural habitats. Here, we compared habitat differences in fouling community composition of different successional ages as well as the impact of predation on those communities. Specifically, we investigated how communities differed with respect to natural (seagrass beds) and artificial (docks) habitats and then exposed previously caged communities to predators to examine prey-specific effects within each habitat and on different aged communities. We found that habitat was a good predictor of community structure including both total species richness and introduced species richness higher in artificial habitats. We expected predators to increase available space allowing increased species co-existence, however, this was not the case. Predators in both habitats reduced richness despite having a strong impact on the percent cover of dominant groups. Predators also reduced introduced species richness, particularly in artificial habitats. Artificial structures are an important pathway of success for introduced species and results here show the importance of biotic resistance within these habitats, potentially limiting the spread of introduced species into natural habitat. Overall, species found within the different habitats could be predicted based on life history traits and predators did not increase the similarity of communities between habitats though still acted in a comparable way, reducing the dominant groups.