636 ANDERSON AND LENAT 



Hexarthra may have been favored by power-plant operation, 

 perhaps through an extension of the period of maximum tempera- 

 ture. Densities in year 6 vi^ere significantly greater (1% level) than in 

 years 4 or 5. 



Ptygura, like Hexarthra, exhibited a seasonal distribution typical 

 of a warm stenotherm (Fig. 7). Ptygura peaked at the highest 

 temperatures of all species studied: 30 to 35°C. Maximum densities 

 were recorded in August, year 6, at temperatures of 32 to 34°C. The 

 extension of the period of maximum summer temperatures may have 

 favored an increase in the standing crop of Ptygura. The average 

 density of Ptygura increased from 1000/m^ in year 4 to 11,400/m^ 

 in year 6. Ptygura is rarely mentioned in the literature as a significant 

 component of the zooplankton. However, collections from Belews 

 Lake do not constitute the only record of Ptygura in Piedmont lakes. 

 Very similar seasonal distributions have been found in Lake Anna, 

 Virginia (Loeffelman, 1976) and in Lake Keowee, South Carolina 

 (Duke Power Company, 1977). These records suggest that Ptygura 

 may commonly occur in lakes of the southeastern United States, 

 although only in the warmest months of the year. 



The distribution of P. ti^uncatum appeared to be unrelated to 

 power-plant temperature effects (Fig. 7). It occurred irregularly in 

 year 4, was absent in year 5, and exhibited a sharp late-summer peak 

 in year 6. Ptygura tj^uncatum is a predacious rotifer (Hutchinson, 

 1967), and its increase in September of year 6 may be related to the 

 increase of such potential prey organisms as Hexarthra and Ptygura. 



The average density of Synchaeta (Fig. 6) increased significantly 

 (5% level) in year 6 when compared to year 4. Several authors have 

 indicated that Synchaeta may be predacious on smaller rotifers, 

 especially Keratella (Hutchinson, 1967). However, such feeding is 

 probably only incidental (Pejler, 1964). Synchaeta peaks usually 

 occur in early spring, preceding peaks by Keratella and other rotifers 

 (Ahlstrom, 1934; Beach, 1960; Pejler, 1962). Pejler (1962) indicated 

 that Synchaeta fed on live algae only, therefore, being favored at the 

 start of the spring pulse. The spring peak of Synchaeta increased 

 from year 4 to year 6 in Belews Lake. Synchaeta feeds on large algae 

 (Pejler, 1957), and its increase may be related to the increase in 

 Peridinium inconspicua (length approximately 15 to 25 /jm). 



Tests for Homogeneity 



We hypothesized that the high power-plant pumping rates might 

 tend to increase the homogeneity of the zooplankton community. 

 This hypothesis was tested in two ways using the analysis of variance 

 techniques discussed earlier. Table 4 illustrates such a test for one of 



