A dynamic oceanographic front drives biogeographical structure in invertebrate settlement along Santa Cruz Island, California, USA

Understanding the factors that determine community diversity is a central focus of ecology and has important implications for conservation and management. We investigated how the local movement of a dynamic front between 2 opposing water masses influenced subtidal invertebrate settlement rates and settlement diversity along the north coastline of Santa Cruz Island, California, USA. Using data from artificial collectors deployed twice per month in 2008 and 2009, we characterized larval settlement of ecologically and commercially important marine invertebrates. We also tracked movement of the front throughout the collection period by analyzing variation in sea temperature at sampling sites. Settlement rates of multiple species of bivalves, gastropods, decapods, and echinoderms were positively associated with the proportion of time a given site spent in a particular water mass. Overall settlement diversity was also related to front location over time, as sites that were exposed to both water masses had higher overall diversity. These results suggest that front movement has a significant impact on settlement and community structure. We also found that these effects applied at several levels of taxonomic resolution, suggesting that our findings are robust to varying levels of identification. Dynamic boundaries may impact overall regional biogeography and community connectivity and lead to communities in the area of front movement having higher levels of diversity. Thus the scale of oceanographic circulation patterns should be considered in conservation and management planning efforts focused on conserving diversity (e.g. the placement of marine protected areas) and in studies of marine population dynamics.