Population persistence of California Current fishes and benthic crustaceans: A marine drift paradox

Because flow in the California Current is unidirectional for months, larvae of coastal species may drift and settle downstream of their parents, potentially causing the parental population to go extinct from upstream to downstream; this is a marine equivalent of the drift paradox in streams. Unidirectional larval drift might, however, be minimized by when, where, and how organisms reproduce. We compiled data on California Current fishes (89 nearshore, 65 shelf/slope) and benthic crustaceans (35 nearshore, 15 shelf/slope) and found three unique sets of life history traits displayed by (1) shelf/slope species, (2) nearshore pelagic-spawning fishes (all from the Southern California Bight [SCB] and Baja California), and (3) all other nearshore species. Pelagic larval durations (PD) of shelf/slope species are long (similar to 136 d); offspring are pelagic winter through summer and are found at depth below the mixed layer offshore. Offspring experience northward flow in winter and southward flow in spring/summer, perhaps minimizing net alongshore drift. Adults are both long-lived and highly fecund. Nearshore species have short PDs (similar to 45 d), and offspring are pelagic during spring/summer upwelling and are found nearshore and near the bottom. Nearshore larvae may experience southwards flow during upwelling and northward flow during relaxation events, minimizing net alongshore transport. Nearshore species have shorter lives and are less fecund than shelf/slope species. Nearshore pelagic-spawning fishes (all from the SCB and Baja) have short PDs (similar to 48 d), but in contrast to other nearshore species, their larvae are pelagic from spring into fall and are found far from shore. Adults are long-lived, highly fecund, and have numerous broods per year. These life history traits may have evolved to exploit eddies and countercurrents present in the SCB and off Baja for larval retention. Each set of life history traits appears to improve chances of offspring recruiting to parental populations. The pelagic phase, rather than being dispersive, may be selected to achieve a migration between larval pelagic and adult benthic habitats.