Fiddler crabs (Uca thayeri) on Florida's east and west coasts show temporally distinct hatching rhythms, correlated with differences in tidal form. Our purpose in this study was to determine whether these differences were fixed or could change in response to variation in the tides. West coast crabs (but not east coast crabs) showed seasonal variation in their hatching rhythms correlated with seasonal variation in the tides. In the spring, they released larvae at night. In the summer, hatching occurred during the day. West coast crabs transferred to Florida's east coast within four weeks released larvae at night in a rhythm similar to resident crabs but different from the spring nocturnal rhythm shown at their home beach. We conclude that this species has a flexible hatching rhythm that changes under natural, as well as under experimental, conditions. Such flexibility may permit the crabs to time larval release optimally over a range of tidal forms. This study and others published recently suggest that “plasticity” may be characteristic of behavioral rhythms shown by many intertidal crabs.