ECOLOGICAL NOTES ON FIDDLER CRABS OF SOUTH TEXAS, WITH SPECIAL REFERENCE TO UCA SUBCYLINDRICA

The distribution of fiddler crabs (genus Uca) in the semiarid zone of south Texas and northeastern Mexico was studied. Up to five sympatric species of Uca can be found in intertidal habitats with salinities below 45 ppt. Each appears to exploit specific segments of the environment by its special ability to use a portion of the available resources. In higher salinity habitats, only one species is found, Uca subcylindrica. It lives at the extreme upper edge of the supralittoral zone and has evolved specializations for a terrestrial existence. In these habitats, Uca subcylindrica burrows to a depth of 1.8 m. Since the feeding apparatus is rarely used in sediment sorting, massive feeding has superseded particulate processing on the desiccated soils. Activity patterns in nature are timed by daily solar events. The phasing of diurnal activity periods varies throughout the year to permit foraging under optimal temperature and humidity. This behavior reflects adaptations of a fiddler crab for occupying one of the more terrestrial arid environments inhabited by a member of the intertidal genus.