Endogenous swimming rhythms underlying the spawning migration of the blue crab, Callinectes sapidus: ontogeny and variation with ambient tidal regime |
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Authors: | M Zachary Darnell Dan Rittschof Richard B Forward Jr |
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Institution: | (1) Duke University Marine Laboratory, Nicholas School of the Environment, 135 Duke Marine Lab. Rd., Beaufort, NC 28516, USA;(2) Present address: Marine Science Institute, The University of Texas at Austin, 750 Channel View Drive, Port Aransas, TX 78373, USA |
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Abstract: | Spawning female blue crabs, Callinectes sapidus, use ebb-tide transport (ETT) to migrate seaward. In estuaries with semi-diurnal tides, ETT in ovigerous blue crabs is driven
by a circatidal rhythm in vertical swimming in which crabs ascend into the water column during ebb tide. The ontogeny of this
rhythm was examined by monitoring swimming behavior of females before the pubertal molt, females that had recently undergone
the molt but had not yet produced a clutch of eggs, and ovigerous females from an estuary with strong semi-diurnal tides.
To assess variation in swimming rhythms with ambient tidal regime, swimming rhythms of ovigerous females from semi-diurnal
(Beaufort, North Carolina), diurnal (St. Andrew Bay, Florida), and non-tidal (South River, North Carolina) estuaries were
compared. Experiments were conducted during the summers of 2006–2008. Female crabs prior to oviposition had variable endogenous
swimming rhythms (circadian, circatidal, or circalunidian). Ovigerous females from estuaries with semi-diurnal and diurnal
tides had pronounced circatidal or circalunidian rhythms with swimming during the time of ambient ebb tide. Swimming rhythms
of several ovigerous crabs switched between circatidal and circalunidian during the ~5-day observation period. Ovigerous crabs
from a non-tidal estuary had a circadian rhythm with vertical swimming around the time of sunset. These results suggest that,
while endogenous swimming rhythms are present in some female blue crabs prior to oviposition, rapid seaward movement via ETT
in tidal estuaries begins following oviposition of the first clutch of eggs. |
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