Nearshore Larval Retention and Cross-Shelf Migration of Benthic Crustaceans at an Upwelling Center

Abstract

Planktonic larvae are thought to be very susceptible to offshore advection in upwelling regimes, increasing dispersal and decreasing recruitment. However, larvae of 42 species of nearshore benthic crustaceans primarily developed on the inner shelf at locations both in (98.5%) and away (99.8%) from a perennial upwelling center in the upwelling season of a recruitment-limited region characterized by persistent, strong, upwelling. During three cross-shelf cruises conducted at each location, larvae of 21 species remained on the inner shelf at both sites by occurring beneath seaward-flowing surface currents while larvae of other species migrated to midshelf (four species) or offshore (14 species) by initially developing near the surface. Postlarvae apparently returned to shore either deep in landward-flowing upwelled water or near the surface where behavior allows them to be transported shoreward by internal waves, diel wind cycles or wind relaxation events. Thus, recruitment limitation in upwelling regimes does not appear to be caused by larval mortality from offshore transport, requiring new research directions to advance our understanding of population dynamics, structure and connectivity.

Effects of ocean climate on spatiotemporal variation in sea urchin settlement and recruitment

“…This index has been used as a large-scale proxy for processes that may favor larval retention and advection from shore in addition to its value as a predictor of coastal productivity (Shkedy and Roughgarden 1997;Wing et al 2003;Menge et al 2011;Menge and Menge 2013). We emphasize that this index is not a location-specific metric nor does it consider fine-scale nearshore hydrodynamic processes that are also likely to affect larval retention (Shanks and Eckert 2005;Morgan et al 2009Morgan et al , 2016Morgan et al , 2018Shanks and Shearman 2009;Fisher et al 2014;Shanks et al 2017;Shanks and Morgan 2018) which remain outside the scope of this study, but worthy of investigation as drivers of settlement trends. Rather we include the Bakun index as an indicator of broader scale coastal upwelling that may affect regional trends in larval supply (e.g., Roughgarden et al 1988).…”

California Current seascape influences juvenile salmon foraging ecology at multiple scales

“…amphipods, decapods, copepods) were the only prey group that was more abundant in salmon diets following low recent upwelling. Relaxation events can be an important period for decapod larvae to settle along the coast, but larvae can be abundant during both relaxation and upwelling periods (Wing et al 1998, Morgan et al 2018. If non-krill invertebrates are relatively abundant across upwelling regimes and krill are more abundant after recent upwelling, our data suggest that juvenile salmon may preferentially feed on krill, and only consume non-krill invertebrates when other more profitable prey are not available.…”

Larval dispersal in a changing ocean with an emphasis on upwelling regions

“…Smaller scale circulation structures that are mostly responsible for transporting larvae generally occur within 10 km of shore (Morgan et al. , ) and are driven by gyre currents and their interactions with coastal topography, the seafloor, and local forces like land breezes and riverine inputs. Larval transport in these small‐scale structures strongly depends on spatial and temporal variation in gyre currents.…”

“…Although larvae of some species are retained nearshore (e.g., pea crabs, Pinnotheroidea) for the duration of development, others migrate far offshore (e.g., cancrid crabs, Cancroidea) before returning to nearshore adult habitats (Morgan et al. , ). Species with larvae that are retained nearshore may face higher mortality in a changing ocean since shallow nearshore waters are expected to change the fastest (IPCC ).…”