Oceanic currents and larval accumulation potentially have large impacts on the choice of locations for marine reserves. Larval settlement of benthic invertebrates was greater in the lee than on the windward side of a small headland during the height of upwelling in central California during 2001 and 2002. Strong upwelling during the study was indicated by mean seasonal Bakun indices of 149 to 176 m3 s-1 per 100 m of coastline in 2001-2002. Weekly sampling of near-surface and near-bottom settlement in the lee of Bodega Head from August 2000 to September 2001 revealed that most larvae of 7 crab taxa settled during spring and summer, which coincides with the upwelling season. Comparison of sites in the protected (lee) and exposed (windward) sides of the headland (2 sites each) during the peak settlement season in 2001 showed that most larvae settled in the lee of the headland, including 91% of crabs, 89% of barnacles, and 80% of mussels in weekly samples. During 2002, weekly sampling at 1 protected and 1 exposed site also demonstrated that most settlement occurred in the lee of the headland, including 74% of crabs, 82% of barnacles, and 65% of mussels. Crabs settled mostly at the surface, whereas barnacles and mussels primarily settled near the bottom, indicating that postlarvae in both surface and bottom waters accumulate in the lee of the headland. Larval accumulation zones should be included in networks of marine reserves to supply adult populations with propagules in recruitment-limited upwelling regions. © Inter-Research 2006.

Delivery mechanisms for crab postlarvae along upwelling coasts have been inferred from weekly sampling, but more frequent sampling is needed to better relate highly variable oceanographic conditions to postlarval supply. Settlement of 8 crab taxa was measured in Bodega Bay, California every 2 d from 12 May through 3 July, 2002. Abundance of postlarval and juvenile settlers was cross-correlated with physical variables. Four upwelling and 4 relaxation events were recorded as fluctuations in wind stress and sea temperature during this period. Transitions to and from upwelling conditions in Bodega Bay were brief and temperature changes occurred rapidly. The strongest correlations between crab abundance and physical variables indicative of upwelling and relaxation conditions were observed for Cancer magister, which settled primarily during relaxation-favorable conditions, and for Cancer antennarius/productus, which settled primarily during upwelling-favorable conditions, suggesting interspecific differences in delivery of postlarvae to adult habitat. Weak correlations with upwelling-favorable conditions were observed for Pugettia producta/richii and Pagurus spp. Settlement of Hemigrapsus nudus, Petrolisthes cinctipes, and P. eriomerus exhibited significant correlations with changes in tidal height. These results highlight the existence of multiple taxon-specific delivery mechanisms of closely related taxa in one small geographic region. © Inter-Research 2006.

Larvae are thought to be highly vulnerable to offshore transport of upwelling regions, limiting recruitment to infrequent wind relaxation and downwelling events. However, larvae could also be transported onshore by upwelled bottom waters, onshore wind-forcing or internal tides throughout the water column. We determined the relative importance of these hypothetical mechanisms for the timing of recruitment of 8 invertebrate taxa during the peak upwelling season in a region of strong, persistent upwelling. Recruitment was determined for 5 yr at an open embayment near the surface and bottom of the water column to examine the interaction of behavioral and physical processes regulating larval recruitment. Postlarvae consistently recruited near the surface or near the bottom depending on the species. Onshore delivery of larvae during wind relaxations and reversals did not best explain recruitment patterns in our area for most taxa. Only mussels consistently recruited more during these events, and they recruited in bottom rather than surface waters. Six crab taxa recruited primarily during upwelling. Recruitment of 7 taxa was intermittently correlated with the maximum tidal range, suggesting that internal waves also may deliver larvae onshore. Thus larvae may recruit by multiple processes in upwelling regions rather than being limited to infrequent relaxation events, leaving the mechanisms responsible for observed spatial patterns in larval recruitment and adult densities unexplained. Comprehensive studies of the behavioral and physical processes underlying larval recruitment and post-settlement mortality are needed to explain observed temporal and spatial variation in population dynamics and community structure in upwelling regions. © Inter-Research 2009.

Larvae are thought to be highly vulnerable to offshore transport in productive upwelling regions, which increases cross-shelf and alongshore dispersal, limits recruitment, and reduces the strength of community interactions. We investigated whether the last planktonic stages of shallowwater crabs (1) occur far offshore during the peak upwelling season in a region of strong upwelling that is recruitment limited, (2) occur farther offshore during upwelling than relaxation conditions, (3) occur farthest from shore at a major headland where currents are deflected offshore, and (4) recruit less during years of stronger upwelling. Crab postlarvae were collected from between 1 and 70 km from shore at 3 locations across an upwelling cell during upwelling and relaxation conditions in northern California, USA, for 3 yr, and recruitment was measured at 2 sites during 2 of these years. Postlarvae of all species collected were most abundant on the inner continental shelf (84%) and were scarce in the open ocean. Postlarvae of 3 taxa only occurred on the inner shelf, whereas postlarvae of the other 3 taxa collected occurred in low abundances on the outer shelf even during prolonged upwelling. They were abundant close to shore at the Point Reyes headland where flow is deflected offshore. Postlarvae did not occur farther from shore during a year of very strong upwelling, and 4 of 7 taxa recruited more then. Thus, crab postlarvae do not appear to be advected far offshore or recruit less during strong upwelling conditions, and the cause and extent of recruitment limitation warrants further investigation. © Inter-Research 2009.