Adaptation to estuarine conditions in shore crabs Carcinus maenas (L.) in relation to body size

Abstract

Analysis of the salt kinetics in a closed medium in which shore crabs Carcinus maenas (L.) are exposed to changes in salinity, yields information on the permeability and the halftime value for salinity adaptation. The latter value represents an index of the extent to which an animal is adapted to salinity fluctuations in its environment. At brackish-water salinities, the overall permeability to salt appears to be inversely related to the external salinity. Sudden changes in the medium salinity result in a rapid, temporary reduction of the permeability. The whole-animal permeability appears to be linearly related to animal weight. The area-specific permeabilities in small animals tends to be lower than those of larger ones. The halftime value for salinity adaptation is found to be independent of animal weight or external salinity. Therefore, small animals will have no disadvantage in the passive internal damping of fluctuations in environmental salinities. This explains why young animals, despite their high surface area:volume ratio, can survive in shallow coastal waters where environmental conditions are highly unstable.