Thurman, C.L.* : Variance in Osmoregulation among Sympatric Fiddler Crabs, genus Uca, from Texas

Osmoregulatory capabilties were measured in five species of fiddler crabs from eight coastal locations in Texas. Specimens were placed in finger bowls containing 50 mls of water ranging in osmolarity from 50 to 3450 mOsm (2 to 110 ppt). Survivorship was recorded for each species. After 3 to 5 days of exposure, the osmolarity of a hemolymph sample was estimated using a Wescor 5520 Vapor Pressure Osmometer. Uca rapax and U. panacea were most hardy over a wide range of media osmolarities. Uca spinicarpa were limited to surviving in media below 1400 mOsm (45ppt). Uca subcylindrica and U. longisignalis were intermediate in survival. U. panacea, U. subcylindrica and U. rapax were equivalent in their osmoregulation between 50(2ppt) and 3200 mOsm (100ppt). U. longisignalis lost it’s ability to regulate above 2200 mOsm (70ppt) while U. spinicarpa ceased to regulate above 1200 mOsm (40ppt). Among the five species, only U. longisignalis exhibited a variance in regulation related to site of collection. These physiological capabilities correlate with the salinity characteristics of the habitats typically occupied by each species.