Synchronization of activity rhythms with the tide in a saltmarsh collembolan Anurida maritima

On a marine saltmarsh, the intertidal collembolan Anurida maritima (Guérin) has a well-defined tidal rhythm of activity on the mud surface between submerging tides: a large proportion of the individuals emerge from their underground refuges shortly after the retreat of the tide, forage there for a few hours, and retire underground at least 1 h before the return of the tide. This activity rhythm has a period of about 12.4 h and it persists in the field during sequences of non-submerging tides and in the laboratory away from the tides in constant light. In the field the level of activity is greatly reduced during the night. It is suggested that the function of this tidal rhythm is to enable individual Anurida to anticipate the return of the tide both during periods of regular, twice-daily tidal submergence and after a period of days when the habitat has not been covered by the tide.