Vertical migration of the crab Carcinus maenas first zoea in an estuary:implications for tidal stream transport

Abstract

ABSTRACT-The f~rst zoea of Carcinus maends (L.) was intensively sampled in the Canal d e Mira (Ria d e Aveiro. Portugal) during the winter and spring of 1990. Each sampling period included a series of 25 h fixed-station plankton sampling cycles (12 in winter and 9 in spring), conducted at 1 station located in the lower part of the Canal. Plankton samples were collected every hour, at several depths along the water column, with the use of a pump. Hydrological measurements (salinity, temperature and current velocity and direction) were taken immediately before the collect~on of the plankton samples. The average depth of the zoeae changed in phase with the tide lal-vae reached their highest position in the water column during e b b and thelr lowest during flood. The extent and phasing of the vertical displacements were such that the first zoea occupied a significantly higher position during the span of the e b b than during flood ( p < 0.001). It was also demonstrated that the larvae were s~gnif~cantly closer to the surface during the night (p < 0.05). The pattern of vertical dispersion of the zoeae changed cyclically, with a period equivalent to the tidal half-cycle. Slaximum aggregation usually occurred during periods of high current velocity and was independent from water stratification. These observations support the hypothesis that C. maenas first zoea performs an active vertical migration synchronised with tidal and daily cycles. Analysis of the zoeae instantaneous velocity showed that shifts of vertical position according to the phases of tide and day Influenced their transport velocity, d u e to vertical differences of water velocity in the estuarine shear current system Durlng e b b the larvae were transported at a velocity that exceeded the vertically integrated water veloc~ty; the reverse relationship was observed during flood ( p < 0.001). The larvae were also transported faster during the night than during the day ( p < 0.05). These results demonstrate that selective tidal stream transport can be generalised in the sense of a unidirectional transport mechanism in estuaries that can enhance exportation.

Comparison between two lunar situations on emission and larval transport of decapod larvae in the Mondego estuary (Portugal)

“…Our study, carried during two different lunar situations, confirms the results of Gonçalves (1991), Paula (1989) and Queiroga (1997) regarding the abundance of the first larval stage of crustaceans decapods for the Portuguese Atlantic coast. Furthermore, the occurrence of crepuscular ebbing tides during both First and Last Quarter Moon is coincident with the higher abundance of the first stage of crustacean decapods, in the estuary of Mondego.…”

Vertical distribution and trophic structure of the macrozooplankton in a shallow temperate estuary (Ria de Aveiro, Portugal)

“…Densities of G. spinifer, S. spiritus and post-larvae C. crangon were significantly affected by the simultaneous interaction of the three factors. The observed patterns for the most abundant species in Canal de Mira (Ria de Aveiro) were in accordance with previous reports from other temperate estuaries concerning gelatinous plankton (Alldredge and Hamner, 1980;Costello and Stancyk, 1983;Esnal et al, 1985), copepoda (Fragoupoulu and Lykakis, 1990;SaintJean and Pagano, 1990), demersal plankton (Williams and Collins, 1984;Orsi, 1986;Mees et al, 1993), as well as fish eggs and larvae of benthic species (Fish, 1979;Barnes, 1981;Christy, 1982;Ré, 1984aRé, ,b, 1987Bachelet and Yacine-Kassab, 1987;Ré, 1990;Paula, 1993;Chase and Thomas, 1995;Queiroga et al, 1997).…”

Endogenous tidal and semilunar moulting rhythms in early juvenile shore crabs Carcinus maenas: implications for adaptation to a high intertidal habitat

“…Larval dispersal no doubt contributes to recent reported marginal diffusion of the species and recent research has shown that combined larval release rhythms at nocturnal high tide and inherited tidal vertical migration rhythms phased to ebb tide enhance rapid offshore dispersal of newly released zoea larvae (Zeng & Naylor 1996a,c,d, 1997, Queiroga et al 1997. Recruitment back to crab populations on coasts takes place at the megalopa stage, facilitated by reversed, flood-phased, upward swimming rhythms.…”