Contrasting effects of coastal upwelling on growth and recruitment of nearshore Pacific rockfishes (genus Sebastes)

Knowledge of processes underlying recruitment is critical for understanding marine population dynamics and their response to ocean climate. We investigated the relationship between coastal upwelling and early life history of black rockfish (Sebastes melanops), a midwater aggregating species, and CQB rockfishes (a solitary benthic species complex including Sebastes caurinus, Sebastes maliger, and Sebastes auriculatus), between two oceanographically distinct years on the west coast of Vancouver Island, Canada. We analysed otolith microstructure to determine parturition and settlement dates, pelagic durations, and pre- and postsettlement growth rates. High CQB rockfish recruitment in 2005 was associated with prolonged downwelling and warm ocean temperatures, late parturition dates, fast presettlement growth, short pelagic durations, and small size-at-settlement. In contrast, high black rockfish recruitment in 2006 was associated with strong upwelling and cool ocean temperatures, slow presettlement growth, and protracted pelagic durations. Presettlement growth of both rockfish complexes increased with high sea surface temperature, but was unrelated to chlorophyll a concentration. Our results indicate that the same oceanographic conditions give rise to fast presettlement growth and short pelagic durations for both groups, but that different factors lead to strong recruitment in each.

Population structure of copper rockfish (Sebastes caurinus) reflects postglacial colonization and contemporary patterns of larval dispersal

The copper rockfish (Sebastes caurinus) is a benthic, nonmigratory, rocky reef species with pelagic larval and juvenile stages lasting several months. Adults are commonly distributed in temperate coastal waters of the Pacific Ocean from British Columbia to southern California, including the inland waterways of Puget Sound, Washington, a semi-enclosed fjord system of known postglacial origin. Here, we report the distribution of genetic variation at six microsatellite DNA loci from six locations throughout the species' range. Among four coastal samples, significant population subdivision was detected (FST = 0.007), and a significant correlation between genetic and geographic distance was observed. Divergence was large and significant between Puget Sound proper and coastal samples (FST = 0.087). A sample taken only 100 km north of Puget Sound (the Canadian Gulf Islands) was also highly divergent from Puget Sound and coastal samples and was genetically intermediate between the two. The Puget Sound sample also displayed significantly lower allelic diversity and a more substantial presence of private alleles. The patterns of genetic divergence and diversity are most consistent with a historical colonization followed by limited oceanographic exchange among geographically proximate locations.