Physical influences on recruitment to California Current invertebrate populations on multiple scales

Studies of recruitment to Dungeness crab (Cancer magister) and red sea urchin (Strongylocentrotus franciscanus) populations have focused on recruitment variability on interannual, 1000-km scales. These studies have identified correlations between recruitment and variables indicating ENSO conditions and wind-forced larval transport. On longer scales. our understanding of biologically important physical variability in the California Current has recently been enhanced by an appreciation of semi-basin, decadal changes. Intensification of the Aleutian low-pressure zone in the mid-1970s had a clear positive effect of biological productivity in the Gulf of Alaska, and less obvious negative effects on productivity in the California Current. On shorter scales, art increasing appreciation of the effect of dispersal patterns on population dynamics and the potential of spatially explicit management schemes provide the impetus for studying processes such as alongshore spatial variability in recruitment and the underlying daily variability in circulation over 100-km distances. In the 1980s, physical studies of coastal circulation in response to daily fluctuations in upwelling winds identified brief periods of northward, onshore How interrupting the offshore, southward flows associated with active upwelling. In the 1990s, concurrent monitoring of biological and physical conditions revealed that these flows transport late-stage invertebrate larvae from a retention zone in the lee of a local promontory to settlement locations, producing specific spatial patterns of recruitment. Variability in recruitment of both crabs and Sea urchins is thus driven by daily temporal variability in upwelling winds and 100-km spatial variability in coastal topography. Interannual recruitment variability appears to depend on ENSO-related biological productivity and larval transport in ways that vary among species. but are not completely understood. Observations are consistent with coastwide, interannual variability being driven by biological productivity (i.e. ENSO/non-ENSO conditions), while the upwelling relaxation mechanism sets the spatial scale, and decadal, semi-basin variability modulates the frequency of ENSO conditions.