Distribution and potential larval connectivity of the non-native Watersipora (Bryozoa) among harbors, offshore oil platforms, and natural reefs

摘要

Non-native marine species thrive on artificial habitat. Expanding coastal infrastructurehas led to concerns that increasing artificial habitat will facilitate the spread of non-native species overall and to natural ecosystems. In the Santa Barbara Channel(SBC), California, USA, the non-native bryozoan Watersipora subatra (Ortmann,1890) has previously been reported only in harbors and on offshore oil platforms.To assess the distribution and potential for spread of W. subatra between coastalinfrastructure and natural habitat in the SBC, we surveyed 61 open coastal sites,including natural and artificial habitat, and evaluated the potential dispersalconnectivity of W. subatra larvae from harbors and oil platforms to natural reefsusing survey results and three-dimensional biophysical modeling. We discoveredthat this bryozoan has invaded natural reefs in the region. W. subatra was presenton approximately 50% of the oil platforms and mainland reef sites, but only 17% ofoffshore island reef sites. Modeling indicated high potential connectivity from oneharbor to the closest reef with W. subatra, 4–5 km distant from the harbor mouth,but dispersal to the more distant sites would likely require intermediate steppingstone sites or anthropogenic transport of spawning adults. Populations on offshoreplatforms, in contrast, were virtually unconnected to reef sites through oceancirculation. The survey data indicated potential opportunities to manage current andfuture invasions through the control of larval sources. In particular, manual removalof small isolated populations on reefs at the northern Channel Islands would reducethis source of larvae to uninvaded areas. Consideration of potential connectivity inthe placement of mariculture infrastructure along the coast with respect to harborsand other sources of non-native propagules could also help to reduce the potentialfor stepwise spread of non-natives to natural reef habitat.