13-5 



Although susceptible to the same thermal and mechanical 

 stresses as zooplankters , phytoplankters possess enormously greater 

 reproductive potential (often doubling population size in less than a 

 day) and thus can more easily accommodate extremely high individual cell 

 attrition rates. High cell attrition rates occur naturally by the cells 

 sinking and by herbivorous zooplankton grazing pressures. Although 

 there is no reason to consider individual phytoplankton cell deaths a 

 significant issue with regard to power plant impact, changes in overall 

 levels of production and standing stock and/or a shift in the kinds of 

 phytoplankton produced in the altered system are potentially real and 

 important considerations (Yentsch, 1977) . 



Phy top lankton 



Studies of New Haven Harbor phytoplankton were based on monthly 

 surface water bottle samples and included estimates of standing crop as 

 well as identification and enumeration of phytoplankton taxa. Standing 

 crop, measured as chlorophyll a concentrations, generally remained at 

 low levels from September through January and was somewhat higher from 

 February through August. There was considerable variability in monthly 

 values, probably due to differences in timing and magnitude of phyto- 

 plankton blooms, which cannot be fully characterized by once-monthly 

 sampling. From 1971 through 1975, major chlorophyll a peaks occurred in 

 spring, siimmer and/or fall. During 1976 and 1977, the frequency of 

 occurrence and magnitude of major chlorophyll a peaks increased and, 

 unlike previous years, major peaks were also observed during late winter 

 (Februairy /March) throughout New Haven Harbor. 



In correspondence with chlorophyll trends , total phytoplankton 

 cell densities tended to increase over the period from 1974 through 

 1977. During 1974 and 1975, peak densities generally coincided with 

 peak water temperatures and day length, during July - August. In 1976 

 there was a large peak in February: in the outer harbor, a decline to a 

 June minimtim was followed by a second peak in August, while in the inner 

 harbor the spring/summer peaks were more sporadic. In 1977 the February 



