Coastal retention and longshore displacement of meroplankton near capes in eastern boundary currents: examples from the California Current

Abstract

Nearshore larval retention mechanisms influence the dispersal and recruitment patterns for a wide variety of meroplanktonic species in eastern boundary regions. Areas of coastal larval retention associated with capes in eastern boundary currents provide important spatial structure to coastal populations of fish and invertebrates through their influence on longshore settlement variability. Some patterns observed in the northern California Current for three meroplanktonic species groups (crabs, sea urchins and rockfish) relative to two such apparent retention features are synthesized. It is found that spatial variability in settlement of crabs is predictable at the scale of headlands. Apparent timing of upwelling intermittency and variability on weekly time-scales, as indicated by temperature change, is critical to interannual settlement variability. The average magnitude of upwelling, measured by an upwelling index, is by comparison a poor predictor of interannual settlement variability. Distribution of planktonic larvae relative to a nearshore retention feature is dependent on taxon. These nearshore retention features may act as reservoirs for some taxa or as conduits to the coast for others, likely depending on larval behaviour, timing and cross-shelf location of release relative to upwelling features. The longshore variability in recruitment created by the above patterns can result in differences in subpopulation productivity. For example, strength of a cohort of sea urchins varies longshore in accordance with proximity to retention features.