4-75 



Any significant change in standing crop may indicate 

 an adverse impact resulting from the heated discharge, 

 and any appreciative alteration in the composition and 

 relative abundance ... constitutes an imbalance in the 

 conunuiiL ty and in<JJcatos possible adverse .im|)<acL. 



Although phytoplankters are susceptible to the same thermal 

 and mechanical stresses as zooplankters , the former possess enormously 

 greater reproductive potential (often doubling population size in less 

 than a day) and thus can more easily accommodate extremely high indi- 

 vidual cell attrition rates, which are also caused naturally by the 

 cells sinking and by grazing pressures. Thus, there is no reason to 

 consider individual phytoplankton cell deaths a significant issue with 

 regard to power plant impact. What should be considered, however, is 

 the potential for changes in overall levels of production and standing 

 stock and/or a shift in the kinds of phytoplankton produced in the 

 altered system (Yentsch, 1977) . 



Most of the studies designed to examine effects of power-plant 

 passage on phytoplankton populations have focused on short-term altera- 

 tions. In general, these studies have illustrated that, in temperate 

 latitudes, production is stimulated during cooler months and inhibited 

 during warmer months (Warriner and Brehmer, 1966; Morgan and Stress, 

 1969) and that biocide addition (not utilized at New Haven Harbor Sta- 

 tion) may be more important than heat in reducing production levels 



(Flemer and Sherk, 1977) . Due to natural variability in phytoplankton 

 standing stock and its dependence on many factors, it becomes difficult 

 to isolate causes of long-term changes in production levels; such assess- 

 ment is particularly difficult in nutrient-enriched areas (such as New 

 Haven Harbor) where standing stock varies considerably among years 



(Flemer and Sherk, 1977) . With respect to changes in the kinds of 

 phytoplankton produced. Carpenter (1973) has demonstrated experimentally 

 that heat addition can accelerate natural succession from diatoms to 

 dinof lagellates ; however, in natural systems, the dynamics of toxic 

 dinof lagellate blooms remain poorly understood. Hanson and Gilfillan 



(1975) , however, have implicated two major aggravators of red-tide 

 conditions: sewage discharge and dredging. 



