The role of macroalgae in structuring a New England fouling community and the implications for floating dock management to ameliorate invasive species

Fouling communities are tractable ecological systems that form on manmade structures in the marine environment where hypotheses about community assembly, disturbance, and species invasions can be tested. While much of this work has focused on sessile invertebrates, on hard substrates in the marine environment, invertebrates and macroalgae, organisms from two different kingdoms, can compete for the same limiting resource, space. In rocky subtidal habitats, research suggests that algae may exclude invertebrates or impact invertebrate post-settlement mortality and, to investigate this in fouling communities, I conducted manipulative experiments on the sides of floating docks. In three out for four experiments, macroalgae did not exclude invertebrates but did alter invertebrate community composition, communities with algae having more native species, mainly molluscs, whereas communities without algae were dominated by invasive species, specifically colonial ascidians. In one experiment, macroalgae also appeared to facilitate invertebrate settlement in the early stages of community assembly, mediated by both algae structure and natural chemical cues. If macroalgae presence in fouling communities can shift the balance of invertebrate assemblages towards those containing native species, this suggests a possible role for macroalgae in resisting invertebrate invasions. Both floating docks and marinas could thus be managed to enhance autotroph persistence and more studies in invasion biology could investigate facilitation, indirect effects, and interactions between organisms from different taxonomic groups.