Responses of estuarine crab megalopae to pressure, salinity and light: Implications for flood-tide transport

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

“…The immediate response of supply of Carcinus maenas megalopae to the amplitude of the tide in the present study is consistent with the immediate responses of megalopae to hydrostatic pressure, salinity and tur-bulence during selective tidal stream transport, which increase with increasing tidal range in megalopae of estuarine species (De Vries et al 1994, Tankersley et al 1995Welch & Forward 2001. These reactions can only be triggered if the megalopae are already in nearshore waters or inside the estuary, resulting in an immediate change in larval concentration in the lower estuary.…”

“…This behavior may enhance concentration of megalopae close to estuarine inlets. As the tide begins to rise, the concurrent increase of pressure and salinity above species-specific threshold levels triggers an ascent in the water column that promotes the transport of the megalopae into the estuary (DeVries et al 1994, Tankersley et al 1995. Swimming is maintained during the whole duration of the flood tide by high levels of turbulence, and during slack-after-high-water the megalopae stop swimming due to decreased turbulence levels and drop to the bottom, where they remain during the ensuing ebb tide, because the salinity drop overrides the effect of turbulence (Welch et al 1999, Welch & Forward 2001.…”

“…In some cases endogenous rhythms synchronised with the tide also assist in upstream STST (DeVries et al 1994). The threshold rates of increase in pressure and salinity necessary to elicit the swimming response during flood (Tankersley et al 1995) may be the basis for the increased abundance during spring tides and for the clear 2 wk pattern detected in meso-tidal systems (Moser & MacIntosh 2001, Paula et al 2001, contrasting with the diffuse pattern detected in systems with a lower tidal range (e.g. van Montfrans et al 1995).…”

Interspecific differences in depth preference: regulation of larval transport in an upwelling system

“…Cues that are more pronounced over the tidal cycle in estuaries, such as salinity and temperature, may select more strongly for tidal vertical migrations in estuarine larvae, including those of many Atlantic species (e.g. Tankersley et al 1995, Carr et al 2004, Lopez-Duarte 2008.…”

Postlarval settling behavior, substrate preference, and time to metamorphosis for red king crab Paralithodes camtschaticus

“…Blue crab megalopae exhibit diurnal vertical migration in offshore water (Forward et al 1997), but the behavior is suppressed by exogenous factors including high light intensity (Forward & Rittschoff 1994) in estuarine waters, so that megalopae are only found there during nighttime flood tides (Tankersley & Forward 1994). Swimming by blue crab megalopae increases with increasing pressure and salinity (which occur during flood tides in estuaries), but decreases with increased light level (Tankersley et al 1995). Megalopae of the shore crab Carcinus maenas exhibit endogenous s\'vimming rhythms coinciding with ebb tides in the laboratory, but appear in ocean surface waters during flood tides, probably due to the influence of exogenous factors (Zeng & Naylor 1996).…”