Cross-shelf distributions and recruitment of crab postlarvae in a region of strong upwelling

Abstract

Larvae are thought to be highly vulnerable to offshore transport in productive upwelling regions, which increases cross-shelf and alongshore dispersal, limits recruitment, and reduces the strength of community interactions. We investigated whether the last planktonic stages of shallowwater crabs (1) occur far offshore during the peak upwelling season in a region of strong upwelling that is recruitment limited, (2) occur farther offshore during upwelling than relaxation conditions, (3) occur farthest from shore at a major headland where currents are deflected offshore, and (4) recruit less during years of stronger upwelling. Crab postlarvae were collected from between 1 and 70 km from shore at 3 locations across an upwelling cell during upwelling and relaxation conditions in northern California, USA, for 3 yr, and recruitment was measured at 2 sites during 2 of these years. Postlarvae of all species collected were most abundant on the inner continental shelf (84%) and were scarce in the open ocean. Postlarvae of 3 taxa only occurred on the inner shelf, whereas postlarvae of the other 3 taxa collected occurred in low abundances on the outer shelf even during prolonged upwelling. They were abundant close to shore at the Point Reyes headland where flow is deflected offshore. Postlarvae did not occur farther from shore during a year of very strong upwelling, and 4 of 7 taxa recruited more then. Thus, crab postlarvae do not appear to be advected far offshore or recruit less during strong upwelling conditions, and the cause and extent of recruitment limitation warrants further investigation.

Shoreward swimming boosts modeled nearshore larval supply and pelagic connectivity in a coastal upwelling region

“…Nevertheless, benthic larvae in these regions are consistently retained near the coast, typically within a few kilometers of shore. These larval distributions are observed along the US west coast Hameed et al, 2018;Morgan and Fisher, 2010;Morgan et al, 2009aMorgan et al, , 2009bMorgan et al, , 2012Morgan, in press;Nickols et al, 2013;Shanks and Shearman, 2009), as well as upwelling regimes off Chile (Bonicelli et al, 2016;Poulin et al, 2002) and the Iberian Peninsula (Bartilotti et al, 2014;dos Santos et al, 2008;Domingues et al, 2012;MartaAlmeida et al, 2006). Larvae may avoid offshore transport by residing subsurface, where currents are weaker or onshore.…”

“…In Smith and Jensen (2015). Vertical behaviors are inferred from Morgan and Fisher (2010), Morgan et al (2009aMorgan et al ( , 2009b and Morgan (in press). End spawning date is the date on which spawning ends plus the pelagic larval duration (PLD).…”

Inverse approach to estimating larval dispersal reveals limited population connectivity along 700 km of wave-swept open coast

“…B 283: 20160370 facilitating retention in slower flows close to shore [26,28,32]. Larvae of most nearshore invertebrates develop in the slowmoving, highly retentive coastal boundary layer by either remaining beneath the fast-moving surface layer or undertaking diel vertical migrations to the surface at night after winds have subsided [25,26,29,31,52]. To evaluate connectivity among populations, all demographic data ideally would be collected during the same reproductive season and year.…”

“…The ability of larvae to regulate transport has been widely underestimated in this region of strong current flow and it is now evident that larvae regulate depth in stratified currents, thereby controlling rates and directions of cross-shore transport [24][25][26][27][28]. Larvae of most nearshore invertebrates complete development in a coastal boundary layer of slower flow close to shore (less than 6 km) by either remaining beneath faster-moving surface currents or ascending only at night (diel vertical migration) after winds have subsided and currents have slowed [26,27,[29][30][31][32]. These behaviours reduce alongshore transport and population connectivity [24,33].…”

Mesoscale advection of Upogebia pusilla larvae through an upwelling filament in the Canaries Coastal Transition Zone (CTZ)

“…It is often difficult to determine the source and fate of marine organisms, because their planktonic larvae spend considerable time developing in ocean currents that may transport them far from their natal populations (Morgan et al 2009a). In our case, following the moulting cycle of U. pusilla larvae through the studied area, it is possible to discern information about their origin.…”