Hatching rhythms of Uca thayeri Rathbun: timing in semidiurnal and mixed tidal regimes.

We compared the timing of larval release by Uca thayeri exposed to different tidal regimes. Crabs on Florida's East Coast experience semidiurnal tides, whereas crabs on the Florida's West Coast experience mixed tides.In both populations, hatching occurred shortly after high tide. On the East Coast, most crabs released their larvae between dusk and midnight, a few days before the maximum amplitude spring tides. On the West Coast, most crabs released their larvae during the afternoon tropic tides of greater amplitude. West Coast crabs may release during the day because ebbing tides at night are too weak for effective transport. Thus, at each location, hatching occurs when phase relationships between the ebbing tides, the light-dark cycle, and tidal amplitude are most favorable. Further study is required to determine whether females on each Coast show fixed responses to each tidal regime, or whether they can alter their hatching rhythms upon exposure to different tides.