| Studies were conducted with the Asiatic clam, Corbicula fluminea, that examined seasonal periodicities in spawning, body condition, and percent tissue water content. In addition, responses of adults to brief (24 hr) and extended (30 d) periods of exposure to toxicants were investigated. These studies addressed the valve closure behavioral response by adults exposed to chlorine, cadmium, and zinc; the effects of these pollutants and temperature on the levels of metal binding protein in adults; and the efficacy of halogens (chlorine and bromine) in providing acceptable levels of Asiatic clam biofouling control.; Spawning periodicity of C. fluminea was monitored weekly for 8 months in 1984. Observations revealed that spawning occurred on three distinct occasions with peaks in release of veligers in June, August, and October. Percent tissue water content and body condition were monitored monthly in 1985. Significant differences in these parameters were observed among certain months and among size classes. Tissue water content and body condition in the largest individuals were inversely related.; Periods of activity (valves parted) and quiescence (valves closed) were determined in the absence and presence of toxicants by continuously monitoring valve movement patterns. Data indicate that the duration of activity periods and toxicant exposure concentration are inversely related. Application of these observations to efforts to control Asiatic clam fouling in industrial water lines resulted in a reduction in the total levels of molluscicide required. Exposure of clams to low levels of chlorine (0.25 mg/L total residual chlorine) induced valve closure that resulted in weakened clams after two weeks that were more susceptible to increased levels of chlorine.; The levels of a metallothionein-like metal binding protein (MBP) in tissues of C. fluminea following exposure to metal and non-metal stressors were also assessed. In general, exposure to dissolved cadmium resulted in significantly greater levels of MBP than either dissolved zinc, chlorine, or temperature extremes (4(DEGREES), 30(DEGREES)C). Analysis of individual organ groups demonstrated an inverse relationship between sites of MBP synthesis (gills, mantle, and adductor muscles versus visceral mass) and mode of exposure to cadmium (dissolved versus food associated). |
