Ocean-estuary coupling in the Oregon upwelling region: abundance and transport of juvenile fish and of crab megalopae

Abstract

Numerous species of fish and invertebrates move between the continental shelf and estuaries during their early life-history. The physical mechanisms that regulate such movement and the extent of coupling between the near-shore ocean and estuaries are poorly understood. It is unclear how, or whether, similar physical mechanisms regulate transport to the outer coast and between the outer coast and estuarine areas. We used high frequency light trap collections at 2 sites, outer coastal and estuarine, to compare the timing and magnitude of the relative abundance of juvenile fish and crab megalopae. The time series of juvenile fish and crab megalopae were statistically compared with physical variables indicative of wind and tidal conditions to identify potential transport mechanisms. Species examined included juvenile Engraulis mordax (northern anchovy), Sardinops sagax (Pacific sardine), Sebastes melanops and S. caurinus (black and copper rockfish), and megalopae of Cancer magister (Dungeness crab), C. oregonensis and C. productus combined (pygmy and red rock crabs), and Pagurus spp. (hermit crabs). The abundances of juvenile E. mordax and S. sagax and C. magister megalopae in the estuary were significantly cross-correlated with abundances at the outer coast (at 0 to -4 d lags). These data support the idea that estuarine ingress may be a 2-stage process with initial arrival in the near-shore as the first stage and subsequent entrance into nearby estuaries as the second stage. Significant cross correlations between species abundance and physical variables indicative of wind-driven transport, both upwelling and downwelling-related, and tidal transport, specifically the spring-neap tidal cycle, were found at both the outer coast and estuarine site. These data indicate that both wind-driven and tidal transport may contribute to the cross-shelf transport and estuarine ingress of organisms.KEY WORDS: Ocean-estuary coupling · Juvenile fish · Crab megalopae · Upwelling region Resale or republication not permitted without written consent of the publisher

settlement of shore crab Carcinus maenas on a mesotidal open habitat as a function of transport mechanisms

“…current relaxation or westward currents, colonisation apparently varies as a function of tide. Our hypothesis is consistent with a 2-step model of larval supply formulated for coastal marine species in general (see Miller & Shanks 2004 for discussion) and supported by Carcinus maenas data from Portugal (Queiroga et al 2006). In addition, the influence of local movements of megalopae on colonisation patterns may be contingent on the overall number of larvae reaching the benthic habitats.…”

“…In the estuaries along the Portuguese coasts, zero time lags suggest STST, although the influence of internal waves cannot be disregarded (Queiroga et al 2006). Following Miller & Shanks (2004) and Queiroga et al (2006), the time lags of 1 to 5 d for Helgoland suggest a combined effect of STST and internal waves on larval colonisation. The STST has been invoked for megalopae invading estuaries: here cues associated with estuarine water (e.g.…”

Tide and wind control of megalopal supply to estuarine crab populations on the Portuguese west coast

“…Crosscorrelograms indicated a delay of 0 d between tidal range and supply of C. maenas megalopae in the present study. This is similar to the studies of Moser & Macintosh (2001) and Paula et al (2001), but differs from the delays detected by Miller & Shanks (2004). Miller & Shanks (2004) found that maximum abundance of C. magister megalopae occurred 4 to 5 d after maximum amplitude of the tide, and they attributed this effect to a combination of onshore transport by internal waves and diel vertical migration on a background of tidal currents.…”

Biological and physical coupling in the lee of a small headland: contrasting transport mechanisms for crab larvae in an upwelling region

“…For example, recruitment of Cancer magister to light traps was positively correlated with upwelling events and tidal forcing in Oregon (Miller & Shanks 2004). However, in Washington, C. magister recruitment to light traps was not significantly correlated with wind events or tidal forcing (Roegner et al 2003).…”

“…The relative importance of larval transport mechanisms can vary among years (Wing et al 2003) and regions (Johnson et al 1986, McConnaughey et al 1992, Roegner et al 2003, Miller & Shanks 2004. For example, recruitment of Cancer magister to light traps was positively correlated with upwelling events and tidal forcing in Oregon (Miller & Shanks 2004).…”