Larval release by the fiddler crab Uca thayeri: Timing and cues used under different tidal regimes

Hatching rhythms of intertidal crabs vary in timing with species, burrow position, tidal regimes and larval vulnerability. Most fiddler crabs time larval release with the nocturnal high fide. This is possible in semidiurnal tidal regimes because there are nocturnal high tides each lunar day. However, mixed tidal regimes have a semidiurnal and a diurnal period. During the diurnal phase high fide occurs in the afternoon. This variation in tidal inundation patterns may influence the timing of larval release. Comparisons between two populations of fiddler crab (Uca thayeri ), exposed to different tidal regimes, indicated they time larval release differently. The population exposed to semidiurnal tides timed larval release with the nocturnal high tide prior to the maximum amplitude tide. The population exposed to mixed tides timed larval release with the diurnal maximum amplitude tide. The differences between the populations can be related to their ecology but other variables may contribute.