EFFECT OF FLUCTUATING LOW-LEVEL CHLORINE CONCENTRATIONS ON VALVE-MOVEMENT BEHAVIOR OF THE ASIATIC CLAM (CORBICULA-FLUMINEA)

Asiatic clams (Corbicula fluminea) exposed to water from the upstream section of East Fork Poplar Creek (Oak Ridge, TN), a stream receiving chlorine-containing industrial discharges, were monitored for changes in valve movement patterns. Individual clams were attached to an autom ated valve-movement monitoring apparatus and suspended in flow-through tanks located streamside. Valve-closure behavior of two clams exposed to untreated water was compared to that of two clams exposed to dechl orinated water for two 18-d periods. Chlorine concentrations in untrea ted water exhibited a pronounced diurnal cycle, fluctuating between a mean daily minimum of 0.02 mg/L total residual chlorine (TRC) during t he day and a mean daily maximum of 0.07 mg/L TRC at night during the s econd monitoring period. In over 2,300 fifteen-minute intervals, clams closed for 0.70 of the intervals while exposed to untreated water, bu t closed for only 0.22 of the intervals while exposed to dechlorinated water. Treatment differences in valve closure were tested by repeated -measures ANOVA. A significant treatment effect (p = 0.026) on valve c losure was found in the first monitoring period. Graphical analysis of valve-closure records revealed diel cycles that differed between trea tments. Clams in untreated water usually opened only near midday, when TRC concentrations were lowest. Clams in dechlorinated water opened m ore often, for longer periods, and appeared to respond to dawn and dus k changes in fight. The valve-closure behavior of clams in untreated w ater effectively minimized tissue exposure to waterborne TRC, presumab ly reducing toxic effects. Valve-closure monitoring in conjunction wit h other studies may help estimate the effect of tissue isolation on th e toxicity or bioaccumulation of waterborne chemicals. Such estimates could improve prediction of toxicological or ecological consequences o f stressful conditions on bivalves.