Electrolyte and water balance in muscle tissue of the crab Hemigrapsus nudus

Abstract

Sodium, potassium, calcium, and magnesium ion concentrations of total muscle tissue, blood and total muscle chloride ion concentrations, and blood and muscle tissue hydration were measured in summer- and winter-adapted populations of the shore crab Hemigrapsus nudus exposed to a series of experimental salinities, and at one temperature. When muscle ion concentrations were expressed as a function of extracellular water, changes in these concentrations were nearly identical to those concentrations found in blood and paralleled blood concentration changes with experimental salinity changes. Blood water content remained constant, and summer animal values were higher when compared with winter animal values. Muscle water content decreased significantly over the range of experimental salinities, approximately 15 g/kg wet weight of tissue decrease for each 25% increase in seawater concentration. Average extracellular volume was calculated for summer-adapted crabs to be 23.6% tissue wet weight and for winter-adapted crabs it was 18.8% tissue wet weight. Possible mechanisms are discussed which may explain how anisosmotic regulation (osmotic and ionic regulation between body fluids and the external environment) and isosmotic regulation (osmotic and ionic regulation between tissue and body fluids) contribute to the adaptation of this crab to an estuarine environment.