Endogenous control of timing of metamorphosis in megalopae of the shore crab Carcinus maenas |
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Authors: | C Zeng E Naylor P Abello |
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Institution: | (1) School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Gwynedd LL59 5EY, North Wales, Great Britain, GB |
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Abstract: | Batches of hundreds of freshly collected megalopae of the shore crab Carcinus maenas (L.) showed persistent circatidal rhythms of moulting to the juvenile crab stage when maintained in constant laboratory conditions.
Peaks of moulting occurred around expected times of high tides, with few megalopae moulting at other times. In larvae collected
offshore, the highest tidally-timed peak of metamorphosis occurred during the second to fifth expected times of high tide,
and metamorphosis of 50% of each batch took about 22 h or longer. In contrast, in larvae collected at the water's edge, 70%
metamorphosed during the first expected episode of high tide, within 6 to 8 h after collection. However, although inshore
megalopae moulted before offshore ones, the tidal timing of moulting remained unaltered whether megalopae were collected at
neaps or springs, from the water's edge or farther offshore, in the presence or absence of natural substratum, and under various
light–dark and salinity regimes. Metamorphosis of C. maenas megalopae around the times of high tides may enhance settlement into the upper intertidal zone. Early juveniles of the crab
apparently prefer that zone as they are most abundant there and, unlike adults, do not undertake up-and-down-shore migration
with tides. The present finding demonstrates, for the first time, endogenous physiological timing of circatidal periodicity
in the metamorphic moult of crab megalopae, suggesting that endogenous factors, as well as exogenous ones should be taken
into account in considering the process of settlement by crab megalopae.
Received: 21 February 1996 / Accepted: 27 November 1996 |
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