Effects of changes in salinity on the apparent water permeability of three crab species: Carcinus maenas, Eriocheir sinensis and Necora puber

Abstract

This study has investigated the apparent water permeabilities (AWP) at different salinities of three crabs Eriocheir sinensis, Carcinus maenas and Necora puber from predominantly freshwater, estuarine and marine habitats, respectively. AWP of the crabs increased significantly in the order E. sinensis, C. maenas and N. puber in correlation with the salinity of their typical habitats. C. maenas is able to alter AWP in response to decreases in salinity. Crabs acclimated for 7 days to salinities of 20 ppt or below had significantly increased water efflux times over crabs acclimated to 33 ppt. Nonacclimated crabs, examined immediately (within 5 h) after transfer from 33 ppt to lower salinities, did not alter the half-times of water efflux significantly, but did alter water influx half-times. E. sinensis did not significantly change its apparent water permeability in response to a lowering of salinity from 33 to 5 ppt. Its permeability is generally very low, and thus the crab is well adapted to life in fresh and estuarine waters. N. puber can reduce its high apparent water permeability (AWP) after 1-day acclimation from 33 ppt to the lower salinity of 25 ppt.