DAILY AND TIDAL PATTERNS OF ACTIVITY IN INDIVIDUAL FIDDLER CRAB (GENUS UCA) FROM THE WOODS HOLE REGION

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Abstract
The motor activity of individual specimens of the fiddler crabs, Uca pugnax, U. pugilator and U. minax, was recorded in actographs in both constant illumination and natural cycles of day-light and darkness. In the natural light cycles an accurate, overt, semi-diurnal tidal rhythm was present in all species. In the case of U. minax the tidal rhythm persisted for at least 46 days. Superimposed on the tidal rhythm was a 24-hour component which consisted of activity between sunset and sunrise. In U. pugnax there was evidence of dissociation of components of the tidal clock system. In constant illumination all species exhibited overt tidal rhythms. In U. minax the rhythm persisted for over a month and clearly exceeded in its period length the natural tidal period of 12.4 hours. Some specimens of U. minax and U. pugilator exhibited transitions from a tide-related pattern to what was apparently a circadian rhythm. Variations in the activity patterns were evident at the species level and within species.