the data base for making future assessments of power plant impacts. 

 These impact assessments eventually depend on how well our present data 

 ba.se defines the natural variability associated with community composition 

 and abundance. Interstation similarities have been identified from 

 1979-1981 and there is an annual pattern to these relationships (Fig. 

 3) . Seasonal trends in community composition and abundance have also 

 been consistent from year to year (Fig. 8). However, the abundances of 

 individual species have been found to fluctuate significantly from year 

 to year (Figs. 13, 14, and 15). Even so, three years of data have 

 provided an assessment of the natural variance associated with these 

 trends and fluctuations and are considered adequate for quantitatively 

 evaluating the ecological significance of future changes in species 

 composition and abundance. 



In summary, the evaluation of exposure panel data collected from 

 1979-1981 suggests that future assessments of power plant impacts can be 

 quantitatively defined. Species area curves indicate that four to six 

 replicate panels can effectively collect fouling and wood-boring species. 

 Trumpet diagrams show a higher degree of confidence in the abundance 

 estimate for total community density than that for individual species. 

 However, the latter statistic is probably more sensitive to environmental 

 impacts. Four replicate samples, appear sufficient to account for 

 interpanel variability using abundance data. Mean abundances for indivi- 

 dual species did not significantly change with an increase in the number 

 of replicate samples. Three years of data have been used to assess 

 natural variability associated with seasonal trends and yearly fluctuations 

 in community composition and abundance. 



31 



