Urine production in the shore crab, Hemigrapsus nudus

Abstract

Urine production was determined for the crab, Hemigrapsus nudus from an estuarine habitat with a seasonal pattern of high salinity – low temperature in winter and low salinity – high temperature in summer. Urine production was measured in crabs collected during winter and summer and held in two salinities, 25 and 75% seawater. Methods used were (1) blockage of nephropores with the physiological adhesive, methyl 2-cyanoacrylate monomer, and measurement of subsequent weight increase, and (2) rate of inulin excretion over four time periods: 6, 12, 18, and 24 h. Blockage and inulin excretion gave urine production rates of 15 to 17% body weight day−1 in 25% seawater. In 75% seawater urine production was estimated by blockage to be 6% body weight day−1 and by inulin excretion to be 12% body weight day−1. Summer crabs in 25% seawater produced urine at a slightly lower rate than did winter crabs. In 75% seawater, no seasonal difference was apparent. Urine production was independent of wet weight of crab. It is suggested that the lower rate of urine production by summer crabs in 25% seawater compared with winter crabs in that salinity is related to their lower haemolymph – seawater osmotic gradient and is an adaptation to lowered summer salinity.