The entraining effect of turbulence on the circa-tidal activity rhythm and its semi-lunar modulation in Eurydice pulchra

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Abstract
Turbulence measurements taken at the water's edge at Derbyhaven beach, Isle of Man, indicated that maximum turbulence on any particular tide predictably occurred at the time of high water. However, long term monitoring failed to record any predictable semi-lunar modulation of the intensity of turbulence. Laboratory experiments showed that cycles of mechanical agitation applied for 2 h every 12 h for 4 days could entrain the endogenous circa-tidal activity rhythm of adult Eurydice pulchra. The effect was the same with shaking in constant light or constant darkness. However, when applied at different phases of an imposed L/D cycle, the synchronizer had a varying effect. The strongest entrainment occurred when shaking was phased to ‘midday’ and ‘midnight’ - a phase relationship paralleled by the high water of spring tides. Minimal synchronizer effect occurred when shaking was applied at ‘dawn’ and ‘evening’, the phase relationship of neap tide high water to the solar day. The varying response is suggested to be the origin of the semi-lunar modulation of activity seen in Eurydice pulchra.

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