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Larval behavior regulates nearshore retention and offshore migration in an upwelling shadow and along the open coast

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Larvae are considered to be highly susceptible to offshore transport, thereby limiting recruitment in productive upwelling regions, except in the recirculation features that form in the lee of headlands. We show that 19 of 20 taxa of nearshore crustaceans were at least as common on the open coast as they were in the lee of a headland in a recruitment-limited region characterized by strong upwelling. Nine of these taxa occurred in high concentrations throughout development, indicating that larvae completed development nearshore in a coastal boundary layer of reduced Ekman transport. Larvae of 9 more taxa were prevalent as early stage larvae, and later stages were uncommon, indicating that larvae migrated offshore. The relative abundance of larval stages largely matched the vertical distributions of larvae in this study and a previous cross-shelf survey at this site, indicating that larval behavior plays a substantial role in determining whether larvae complete development nearshore or migrate offshore later in development. Larvae of taxa that occurred nearshore in high concentrations throughout development resided below a shallow Ekman layer of seaward-flowing surface waters, whereas most larvae of the other taxa occurred closer to the surface. Whether larvae undertook ontogenetic and diel vertical migrations also appeared to determine whether they were retained nearshore. Thus larval retention may be more widespread in upwelling regions than is widely believed, and the cause of recruitment limitation along upwelling coasts needs to be determined to further advance our understanding of the connectivity, dynamics and structure of coastal populations. © Inter-Research 2010.

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