Semi-Lunar Variations of Endogenous Circa-Tidal Rhythms of Activity and Respiration In the lsopod Eurydice pulchra

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Abstract
When collected from the shore and placed into IR beam actographs in constant darkness at 15.degree. C in the laboratory, individual adult E. pulchra Leach exhibit an endogenous circa-tidal rhythm of spontaneous swimming activity. Periodogram analysis of activity traces indicates a semi-lunar modulation in the rhythm''s expression. It is most strongly expressed in isopods collected during spring tide periods. Groups of E. pulchra in moist sterilized sand were maintained in Gilson respirometers under constant darkness at 15.degree. C; subsequent recordings of their respiratory rate demonstrated an endogenous circa-tidal rhythm of O2 uptake, with peak rates at the time of expected high water. This rhythm was expressed during spring tide, but not neap tide periods. Relationships of circa-tidal rhythms, their semi-lunar modulations and the semi-lunar emergence pattern of E. pulchra are discussed.