DENSITY (units/ml) 
92 Michael A. Mallin 
MONTH 
PHYTOPLANKTON DENSITY 
CHLOROPHYLL a 
Fig. 2. Total phytoplankton densities and chlorophyll a values in Sutton 
Reservoir during 1985. 
Zooplankton densities (Table 4) were dominated by rotifers and 
were high relative to other North Carolina reservoirs (Weiss et al. 1975, 
DPC 1977, Mallin 1986). Zooplankton biomass values (Table 4) 
indicated biomass dominance by copepods followed by cladocerans and 
then rotifers. Zooplankton biomass in Sutton is low compared with 
other North Carolina impoundments (Mallin 1986). 
Temporal changes in dominance by organism density are illustrated 
by the percent compostion over time of the total density by the major 
taxa groups (Fig. 3). Rotifers comprised large percentages of the 
densities in all seasons except spring. When the composition of biomass 
in Sutton Reservoir is examined over time (Fig. 4), it is evident that 
rotifers constitute a very small percentage of the zooplankton biomass, 
which has two notable peaks each year. In spring the major contributors 
to biomass were the copepod Eurytemora affinis followed by the 
cladocerans Daphnia ambigua, Ceriodaphnia quadrangula, Diaphano- 
soma brachyurum, Bosmina coregoni , and B. longirostris. In the fall, 
CHLOROPHLLa (mq/I) 
