Larval recruitment in a region of strong, persistent upwelling and recruitment limitation

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.