EXECUTIVE SUMMARY 



The Millstone Nuclear Power Station (MNPS) is located on the north 

 shore of Long Island Sound in Waterford, Connecticut. The station 

 consists of two operational units with a combined cooling water flow of 

 2,155 cfs, and a third unit under construction. 



Extensive studies of the potential impact of MNPS on Long Island 

 Sound were initiated in 1968. They have been modified and updated to 

 assure that the best currently available monitoring procedures were 

 used. This report presents 1983 results and provides comparisons with 

 previous years as a basis for impact assessment. 



ZOOPLANKTON ECOLOGY 



The species composition and abundance of zooplankton collected at 

 inshore and offshore stations during 1983 were examined. More than 80 

 taxa were identified during 1983 and a total of 130 since 1970. Six 

 major groups, copepods, cirripedians, gastropods, decapods, cladocerans 

 and amphipods accounted for more than 99% of the individuals collected 

 in 1983, and at least 96% since 1970. Copepods contributed more than 

 88% of the total in 1983; this group has consistently accounted for over 

 79% of the total in each year since 1976. The abundances of Acartia 

 tonsa and A. husonica, the two dominant copepods were higher in 1983 

 than in any of the previous eight years. 



During 1983, as in all previous years, distinct winter-spring and 

 summer-fall communities were identified at MNPS; these were similar to 

 zooplankton communities in LIS and BIS. Inshore (Entrainment) , offshore 

 (Niantic Bay) , and diel differences in zooplantkon densities during 1983 

 and since 1970 were attributed to natural variation since similar 

 patterns have been observed in other areas of Long Island and Block 

 Island Sound. 



As a result, we conclude that any changes observed in the zooplankton 

 communities over the past twelve years were natural and not due to 

 operation of Millstone Nuclear Power Station. 



