MCFADDEN, A; THURMAN, C.L.*; University of Northern Iowa: Osmoregulation by Fiddler Crabs (genus Uca) from California and south Florida

Nine species of fiddler crabs belonging to three subgenera (Boboruca, Celuca and Minuca) were collected for osmoregulation studies from 38 locations in south Florida as well as one site at Mission Bay in California. The Celuca from California, U. crenulata, had hemolymph of 912 mOsm after collection from a habitat of 917 mOsm. Eight Uca spp. were examined from Florida. The Boboruca, U. thayeri,collected from 7 habitats (371 to 1010 mOsm), had hemolymph averaging 794 mOsm. Among the Celuca, U. speciosa, found in 14 habitats (170 to 1039 mOsm), had hemolymph averaging 836 mOsm. Uca pugilator, collected at 28 locations (54 to 1039 mOsm), had hemolymph of 868 mOsm while U. leptodactyla, found in only 2 habitats (732 and 1029 mOsm), had hemolymph of 882 mOsm. Among the Minuca, U. minax, collected in 371 mOsm, had hemolymph of 626 mOsm, U pugnax from 371 and 470 mOsm had hemolymph of 710 mOsm, and U. burgersi from 611 and 1029 mOsm had hemolymph of 843 mOsm. Uca rapax, collected from 19 locations (73 to 1029 mOsm), had hemolymph of 828 mOsm. In the laboratory, crabs were exposed to sea water ranging from 38 to 3550 mOsm for five days. Afterwards hemolymph osmolality was measured. The LC₅₀ for U. thayeri, U. speciosa, U. rapax, U crenulata, and U. pugilator were 2250, 2310, 2800, 2910 and 3082 mOsm, respectively. The isosmotic hemolymph concentration (mOsm) was estimated for U. rapax (780), U. speciosa (798), U. thayeri (819), U. pugilator (879), and U. crenulata (888). Osmotic adaptation was found to be equivalent in U. crenulata and U. pugilator. Among the five species only U. thayeri and U. speciosa were unable to tolerate medium >2600 mOsm. Consequently, U. rapax, U. crenulata, and U. pugilator are considered as the better hyporegulators enabling them to live in euryhaline habitats. Research support provided by Merck-AAAS Summer Interdisciplinary Science Research, UNI-RRTTC and UNI-Graduate College grants.