The effect of salinity on coelomic fluid osmolyte concentration and intracellular water content in Luidia clathrata (Say) (Echinodermata: Asteroidea)

Abstract

1. 1. The concentrations (mM) of osmolytes in the coelomic fluid of Luidia clathrata kept at 25‰S seawater (control individuals) were: 345, Na +; 10, K +; 10, Ca 2+; 44, Mg 2+; 387, Cl −; 0.67, amino acids; 0.09, NH 4 +. 2. 2. When individuals were transferred from 25‰S to 15‰S or 35‰S, the concentrations of inorganic ions in the coelomic fluid usually equilibrated within 24hr and became the same as those in the medium. 3. 3. The intracellular water content (g intracellular H 2O/g solute-free dry tissue) of the pyloric caeca and tube feet of control individuals throughout the experiment was 2.13 and 5.40, respectively. 4. 4. In tissues of individuals transferred to 15‰S, the intracellular water content increased by an average 50% in 12 hr but returned to 19% above control levels during 1 week. 5. 5. In tissues of individuals transferred to 35‰S, the intracellular water content decreased by an average 17% in 12 hr and did not change during 1 week. 6. 6. Luidia clathrata is an osmoconformer and partial cell volume regulator within the seasonal salinity range it encounters.