Salt and water balance and antennal gland function in three pacific species of terrestrial crab (Gecarcoidea lalandii, Cardisoma carnifex, Birgus latro). I. Urine production and salt exchanges in hydrated crabs

Abstract

AbstractRates of inulin clearance and urine production were determined in Gecarcoidea lalandii on full‐strength seawater‐moist sand, in Cardisoma carnifex on 800 mOsm seawater‐moist sand; and in Birgus latro with access to distilled water for drinking. Urine production in G. lalandii was 3.4 ± 0.6 ml·100 g−1·d−1, and the inulin U/B ratio was 0.77 ± 0.01 (n = 6). The urine production rate for C. carnifex was 3.2 ± 0.5 ml·100 g−1·d−1, and the inulin U/B ratio was 0.95 ± 0.01 (n = 6). We were unable to collect urine from B. latro, but the inulin clearance rate was over twice that observed in either G. lalandii or C. carnifex. The inulin U/B ratios we observed were less than unity, which indicated a secretion of fluid into the urine. In general, this secreted solution was slightly hyperosmotic, isoionic with respect to sodium and slightly hyperionic with respect to chloride, but appeared to be of minimal use in salt regulation. Unidirectional sodium fluxes were determined in C. carnifex and B. latro, and compared with the estimated urinary sodium fluxes. The antennal gland appears to be the major site of sodium loss. Under our experimental conditions, the antennal gland was the major site for the loss of salt and water, and it appears to be of minimal use in the retention of salts.