Mechanisms regulating estuarine ingress of blue crab Callinectes sapidus megalopae
Mechanisms of shoreward transport and estuarine ingress in blue crab Callinectes sapidus megalopae have been difficult to infer from time series of nightly settlement on passive hog's hair collectors. We attempted to investigate the hypothesis that separating mechanisms of shoreward transport and estuarine ingress might enable identification of important transport mechanisms by eliminating interactions between wind-driven, tide-driven or other mechanisms. To this end, we collected megalopae simultaneously at nearby coastal and estuarine locations. Megalopae were collected nightly on hog's hair collectors from June to November 2004 to 2006 near the entrance to the Newport River estuary, North Carolina, USA, and at a site within the estuary. Nightly relative abundance of megalopae was cross-correlated with wind stress, maximum daily tidal range and the duration of nighttime flood tides. Relative abundance at the coastal site was not consistently correlated with wind stress or tidal range, possibly due to behavioral responses to turbulence, preventing us from separating the effects of shoreward transport and estuarine ingress. Relative estuarine abundance was positively correlated with: (1) downwelling-favorable winds, (2) onshore winds, and (3) the duration of nighttime flood tides. Hurricanes were associated with the highest estuarine abundance in each year. There was an apparent relationship between the peak months of estuarine ingress and a period of downwelling-favorable winds in September and October known as mariners' fall. A conceptual model is proposed describing the environmental conditions under which estuarine ingress of C. sapidus megalopae occurs. © Inter-Research 2009.
Ogburn, MB; Diaz, H; Forward, RB
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