Anthropogenic structures as a spatial refuge from predation for the invasive bryozoan bugula neritina

Anthropogenic structures may play an important role in the marine invasion process by providing novel artificial habitats, often out of the reach of common benthic predators. A survey of piers in northern-central Chile revealed a change in the epibenthic assemblage on pilings at different distances from a rocky shore with abundant grazers and predators. Pilings on soft sediment, away from the rocky shore, were heavily colonized by the invasive bryozoan Bugula neritina. We therefore hypothesized that benthic predators may forage on pilings located on rocky bottom whereas pilings on soft sediment benefit from the absence of generalist benthic predators which do not occur on soft sediment. We examined piling communities using cages directly attached to pilings, where we included or excluded the sea urchin Tetrapygus niger and the rock shrimp Rhyncocinetes typus. Resultant communities differed substantially; a high percentage of bare space occurred in the presence of sea urchins, while turf algae dominated in the presence of shrimp. Both sea urchins and shrimp suppressed the colonization of the invasive B. neritina and, when acting together, totally prevented its recruitment. In contrast, invasive bryozoans colonized 95% of the available substratum in cages where predators were excluded. Our results show the important role of benthic generalist predators in limiting the establishment and spread of non-native species on anthropogenic structures. Further, this study highlights the unprecedented role of shrimp grazing in structuring hard-bottom communities. © Inter-Research 2011.link_to_subscribed_fulltex