Tidal, daily, and lunar-day activity cycles in the marine polychaete Nereis virens

The burrow emergence activity of the wild caught ragworm Nereis virens Sars associated with food prospecting was investigated under various photoperiodic (LD) and simulated tidal cycles (STC) using a laboratory based actograph. Just over half (57%) of the animals under LD with STC displayed significant tidal (12.4h) and/or lunar-day (24.8h) activity patterns. Under constant light (LL) plus a STC, 25% of all animals were tidal, while one animal responded with a circadian (24.2h) activity rhythm suggestive of cross-modal entrainment where the environmental stimulus of one period entrains rhythmic behavior of a different period. All peaks of activity under a STC, apart from that of the individual cross-modal entrainment case, coincided with the period of tank flooding. Under only LD without a STC, 49% of the animals showed nocturnal (24h) activity. When animals were maintained under free-running LL conditions, 15% displayed significant rhythmicity with circatidal and circadian/circalunidian periodicities. Although activity cycles in N. virens at the population level are robust, at the individual level they are particularly labile, suggesting complex biological clock-control with multiple clock output pathways.