The physiological ecology of the estuarine clam Rangia cuneata (Gray)

Rangia cuneata (Gray, 1832), an estuarine lamellibranch of the marine family Mactridae, is found in areas subject to salinity fluctuations ranging between 0 and 25°/oo. As adults these clams are capable of surviving several months in freshwater and at least two months in full-strength seawater. The present study was conducted to determine the effect of environmental salinity variation on selected physiological parameters. At salinities of 5°/oo or less Rangia responds by maintaining its blood osmotic concentration at approximately 60 m0sm/liter above the medium. Uptake of dissolved glycine is sharply reduced at salinities below 5°/oo, but between 6 and 25°/oo there was no significant difference in the rate of glycine uptake by whole animals or isolated gill tissue. ..