Settlement and transport of benthic invertebrates in an intermittent upwelling region

Abstract

We monitored settlement of sea urchins (Strongylocentrotus spp.) and crabs (primarily Cancer spp.) and concurrent physical variable:; at Bodega Marine Laboratory (BML) and Salt Point (northern California) fromApril through August 1992.lJpwelling favorable winds led to lower temperatures, higher salinities, and lower subsurface pressures at BMI,, while periods of relaxation from upwelling typically caused a lagged reversal of each of these trends. This response to relaxation was due to a combination of alongshore and onshore flow of near-surface water at this site. Crab settlement was significantly correlated with the rate of temperature increase, corresponding to relaxation events. In contrast, sea urchins settled primarily during an unusual relaxation event which poss,ibly involved remote forcing. Sea urchin and crab settlement were negatively correlated. Possible reasons include residence in different water masses, different biomechanical characteristics, and predation by crab larvae on sea urchin larvae. The time-course of settlement at Salt Point was similar to that at BML for bloth species groups.Although transport and nearshore oceanographic conditions have been a focus of settlement investigations since the early days of larval ecology (Young 1990), many questions remain regarding physical oceanographic influences on the transport and settlement of marine invertebrate larvae in the coastal ocean. 'The specific transport mechanisms underlying successful settlement have been identified for only a few species (e.g. Shanks 1986; Roughgarden et al. 1988; Farrell et al. 199 1). Several recent studies have focused specifically on the role of variable coastal winds in larval transport and settlement (e.g. Johnson et al. 1986; Hobbs et al. 1!)92). In this study, we Acknowledgments

Recruitment of coastal fishes and oceanographic variability in central California

“…Relaxation or reversals in wind stress can lead to downwelling conditions where the warmer offshore surface waters and the coastal fronts are advected back onshore, delivering entrained larval organisms to the nearshore benthic habitat (Roughgarden et al, 1988;Farrell et al, 1991). Several studies have shown that variable recruitment of coastal organisms is related to upwelling dynamics in the California region (Parrish et al, 1981;Hollowed et al, 1987;Ebert and Russell, 1988;Roughgarden et al, 1988;Larson et al, 1994;Wing et al, 1995b;Connolly et al, 2001;Broitman et al, 2005;Laidig et al, 2007).…”

“…The west coast of North America is an eastern boundary ecosystem where spatial and temporal variation in larval recruitment can be influenced by the dynamics of wind-driven coastal upwelling (Parrish et al, 1981;Mooers and Robinson, 1984;Norton, 1987;Graham et al, 1992;Wing et al, 1995b;Connolly et al, 2001). Equatorward wind stress displaces coastal surface waters offshore via Ekman transport, which are replaced by colder, nutrient rich, subsurface waters (Huyer, 1983).…”

“…The ocean circulation processes that facilitate the transport of larvae to nearshore benthic habitats take place across a mosaic of spatial and temporal scales (Shanks, 1995;Caley et al, 1996) and have been implicated as key determinants of year class strength for a number of nearshore benthic species (Parrish et al, 1981;Hollowed et al, 1987). Accordingly, a large body of research has been concerned with establishing the mechanisms, either physical or biological, that generate variation in larval recruitment rates (Parrish et al, 1981;Gaines and Bertness, 1992;Levin, 1994;Wing et al, 1995b;Schmitt and Holbrook, 1996;Botsford, 2001;Morgan, 2001;Hughes et al, 2002).…”

Possible effects of downwelling on the recruitment of coral reef fishes to the Eilat (Red Sea) coral reefs

“…These currents are usually driven by wind, which is one of the three principal agents controlling the movement of larval fish and invertebrates on the continental shelf (Epifanio and Garvine 2001). Evidence indicates that these currents might affect the recruitment of invertebrates such as crabs (Blanton et al 1995;Wing et al 1995;Shanks 1998), clams (Weissberger and Grassle 2003;Ma 2005;Shanks and Brink 2005), sea urchins (Wing et al 1995), annelids (Verdier-Bonnet et al 1997), and others, although the association with the vertical current might be weak (e.g., Shanks 1998). However, only a few studies have explained the differences found in the recruitment intensity of fish as due to upwelling or downwelling flow (Reiss and McConaugha 1999;Miller and Shanks 2005), and none of these have referred to coral-reef fishes.…”

“…Upwelling and downwelling are characterized by flow to different (mostly opposite) directions near the bottom and at the surface. Thus, passive or nearly passive larvae that are situated at different depths might be transported to different directions (on-or offshore; Roughgarden et al 1991;Blanton et al 1995;Wing et al 1995), although there is evidence that even very weak swimming larvae will not necessarily be carried by the on-and offshore currents (Shanks and Brink 2005). However, unlike most other larvae, reef-fish larvae have well-developed swimming abilities (Stobutzki and Bellwood 1994;Stobutzki and Bellwood 1997) and hearing and olfactory senses (Sweatman 1988;Atema et al 2002;Lecchini et al 2005a) that can help them to find their settlement site while proceeding against the flow.…”