Population dynamics of the Asiatic clam, Corbicula fluminea (Muller) in the Lower Connecticut River: Establishing a foothold in New England

摘要

The founding population of Corbicula fluminea in the Lower Connecticut River. discovered in 1990, was studied for ten years (1991-2000), Seasonal abundance of six size classes was monitored near three electric power plants. Corbicula abundance varied seasonally as well as annually, but peaked in 1992. Winter survival of clams was positively correlated with the average winter water temperature and negatively correlated with frequency of daily mean water temperatures less than or equal to1degreesC and with frequency of daily mean April spring freshet flows greater than or equal to1700 m(3)/s. Higher winter survival at Middletown Station sites during most years, when compared with survival near Connecticut Yankee, was attributed to the influence of the Middletown Station thermal discharge. Thermal discharge did not support a permanent population at Connecticut Yankee because of temperature extremes during power plant operation in summer. Clam growth under ambient river temperatures began in May when water temperatures exceeded 10degreesC and ceased in December when temperatures fell below this threshold. Cooling water discharges altered this seasonal growth pattern: growth began in November, as temperatures fell below 35degreesC, and ceased in the summer, when discharge temperatures exceeded this upper thermal threshold. Reproduction occurred in the river when water temperatures were between 17degreesC and 28degreesC, typically from June to October. Peak spawning occurred in August. Discharge temperatures shifted clam reproduction back to spring (March to May). The key to Corbicula's success in establishing a population in the Connecticut River is its ability to colonize refugia from winter temperature and spring freshet flow extremes that often cause high clam mortality.