Absence of overall feedback in a benthic estuarine community: A system potentially buffered from impacts of biological invasions

Species introductions are among the most dramatic human-induced impacts on aquatic and terrestrial ecosystems around the world. Stability patterns of an estuarine benthic community were investigated through guild interaction models representing the community before and after human-mediated species i nvasions. The study area was Yaquina Bay, a developed estuary on the centra l Oregon coast, U.S., where at least 12 species of nonindigenous invertebra tes have been inadvertently introduced. Three of the introduced species (th e polychaetes Hobsonia florida and Pseudopolydora kempi and the cumacean Ni ppoleucon hinumensis) are probably among the 10 most abundant invertebrate species in the intertidal benthic community. To estimate effects and potent ial risks of species introductions on the native community we constructed 2 types of community models based on functional-group interactions, namely, activity guild models and trophic guild models. In both cases we observed t hat overall feedback has a strong tendency towards zero in pre-invasion and post-invasion models. We generated 12,000 random models of similar size an d could not detect this tendency. We suggest that the weak or absent overal l feedback in this community may be an ecological property and not an intri nsic property of large systems as such. The reduced response to input from either invertebrate invasions or removal of native top predators, may to so me extent buffer the community from such impacts. Alternative guild models suggested increased risk of stability decline in the invaded community even after accounting for potential complexity effects on stability. Further sp ecies introductions in this intermediately invaded estuary should be avoide d.