Observations on the tidal activity rhythm of the periwinkleLittorina nigrolineata(Gray)

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Abstract
The spontaneous activity pattern of the periwinkle L. nigrolineata has been studied by direct observation in the field and under controlled conditions in the laboratory. In the laboratory the animals are induced to crawl by both immersion and exposure under simulated tidal conditions, and the increased activity following emersion has been confirmed by field observations. Animals kept submerged under constant conditions show an endogenous activity rhythm with a free running period of about 12 to 13 hours. The main activity periods occur about 2 hours after the onset of inundation and the rhythm rephases almost immediately to the time of immersion. There is also evidence for a further endogenous component with peaks corresponding to the time of subjective emersion. The rhythm is modulated on a circadian basis, and is less pronounced during the neap tide period, and during the winter months.