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A Comparison Of Osmoregulation Among Subtropical Fiddler Crabs (Uca) From Southern Florida And California

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Bulletin of Marine Science





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Fiddler crabs were collected for osmoregulation studies from 36 locations in Florida and one at Ocean Beach, California. The responses of five species of Uca from subtropical habitats along the Pacific, Atlantic, and Gulf of Mexico coasts of the U.S. to osmotic stress were examined and osmotic measurements are presented for the first time in three of the species. In artificial seawater (ASW) < 300 mOsm, Uca speciosa (Ives, 1891) Uca rapax (S. I. Smith, 1870), and Uca pugilator (Bosc, 1802) survived at lower concentrations than either Uca crenulata (Lockington, 1877) or Uca thayeri M. J. Rathbun, 1900. In ASW > 2500 mOsm, U. rapax, U crenulata, and U. pugilator had higher survival than either U. speciosa or U. thayeri. Prior to measuring hemolymph osmolality, fiddler crabs were exposed to ASW ranging from 26 to 3550 mOsm for 5 d. The isosmotic hemolymph concentration ([ISO]) was estimated to range from 780 mOsm in U. rapax to 888 mOsm in U. crenulata. The pattern of acute acclimation to hypotonic ASW (195 mOsm) in two euryhaline species, U. crenulata and U. pugilator, was very similar. Results of this study indicate that U. crenulata and U. pugilator are better hyporegulators, enabling them to live in euhaline and hypersaline habitats. Due to a broad range of tolerance and low [ISO], U. rapax is best equipped for living in brackish habitats. In contrast, U. thayeri and U. speciosa are best suited physiologically to inhabit low and moderately saline habitats. © 2005 Rosenstiel School of Marine and Atmospheric Science of the University of Miami.


Department of Biology

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