Settlement and transport of benthic invertebrates in an intermittent upwelling region

Abstract

We monitored settlement of sea urchins (Strongylocentrotus spp.) and crabs (primarily Cancer spp.) and concurrent physical variables at Bodega Marine Laboratory (BML) and Salt Point (northern California) from April through August 1992. Upwelling favorable winds led to lower temperatures, higher salinities, and lower subsurface pressures at BML, while periods of relaxation from upwelling typically caused a lagged reversal of each of these trends. This response to relaxation was due to a combination of alongshore and onshore flow of near‐surface water at this site. Crab settlement was significantly correlated with the rate of temperature increase, corresponding to relaxation events. In contrast, sea urchins settled primarily during an unusual relaxation event which possibly involved remote forcing. Sea urchin and crab settlement were negatively correlated. Possible reasons include residence in different water masses, different biomechanical characteristics, and predation by crab larvae on sea urchin larvae. The time‐course of settlement at Salt Point was similar to that at BML for both species groups.