EFFECTS OF POWER-PLANT OPERATION ON ZOOPLANKTON 627 



and Selcnastruin), which constitute a prime source of food available 

 to microconsumer zooplankton. Few differences can be seen 

 between years, except for an increase in the fall of year 5. 



Figure 3 also presents data on changes in phytoplankton 

 biovolume. This line primarily reflects changes in the large, or net, 

 algal species. Biovolume declined slightly in year 6 with the 

 appearance of Synedra, a long needle-shaped diatom, as an important 

 component of the net phytoplankton. No important decline in 

 biovolume was noted in year 5, but a species change occurred, with 

 Melosira italica var. alpigena being replaced by the larger Peridinium 

 spp. This successional sequence from years 4 to 6 may have caused a 

 decline in the availability and food value of the phytoplankton 

 because Peridinium and Synedra are larger in size and thus would be 

 more difficult to consume. 



Planktivores 



One major change occurred in the planktivore population at 

 Belews Lake during this study. Threadfin shad (Dorosoma petenense) 

 were introduced into the lake by local sportsmen. Data supplied by 

 the North Carolina Wildlife Resources Commission show that 

 threadfin shad increased from a density of 1.3/ha (average of 

 eight coves totaling 3.24 ha) in September of year 5 to 6463. 4/ha in 

 September of year 6 (Scott Van Horn, fishery biologist, personal 

 communication). They declined to year-5 levels in September of 

 year 7. Changes in the zooplankton community did not reflect the 

 appearance and disappearance of this planktivore. For instance, 

 crustacean populations that would be fed upon by young-of-the-year 

 shad in the spring and summer (Applegate and Mullan, 1969) did not 

 show declines in their spring— summer peaks in year 5 (Fig. 4). 



Seasonal Abundance of the Major Zooplankton Taxa 



Figure 5 shows the seasonal distribution, years 4 to 6, for 

 Rotifera, Cladocera, and Copepoda. Several major trends are evident. 

 Rotifers were numerically dominant in Belews Lake, comprising 

 81.2% of the total zooplankton in year 4, 72.1% in year 5, and 

 77.0% in year 6. Cladocera comprised only 7 to 9% of the total 

 zooplankton during this period, and Copepoda (including nauplii) 

 made up 11 to 19%. Rotifera generally exhibit a marked spring 

 density peak. This peak was markedly lower in year 6 than in years 4 

 and 5. Winter densities of Rotifera appear to be increasing over the 

 period of years 4 to 6. However, no significant differences (5% level) 

 were noted between years when all months were considered together. 



