The brackish water clam Rangia cuneata as indicator of ecological effects of salinity changes in coastal waters.

In the search for a laboratory test that could be used to determine when estuarine salinity changes were favorable or unfavorable, salinities in the range from 0 to 38 were tested on adult Rangia clams for effects on survival; regulation of internal salinity ; intake, use and release of amino acids; respiration; glycogen use under aerobic and anaerobic conditions; feeding rate; ciliary activity; uptake of glucose; glycogen storage and 'index of condition' in natural environments through a seasonal cycle; carbohydrate-digesting enzymes; and reproduction. It was determined that Rangia cuneata has a system of compensating reactions that allows it to adjust to changes in salinity over the range from 0 to 38 ppt and over the temperature range from 10 to 35 C without harm. It was concluded from these and further studies that the key to the welfare of a Rangia population is not the physiology of the adult individuals, but reproduction and recruitment. The keys to the use of Rangia cuneata as an indicator were found to be two facts: (1) a change in salinity, either up from near 0 or down from 15 ppt and above, is necessary to induce spawning; (2) the embryos and early larvae can survive only in salinities between 2 and 10 (or 15) ppt.