Sedgwick-Rafter cell, but when this was not possible counts were done within a 
few days of collection on samples preserved with Lugol’s iodine. 
Zooplankton biomass was measured on split fractions of a pooled sample 
of two 1-m net tows from each tank. The sub-samples were rinsed with 
deionized water, lyophilized and weighed. 
The greatest part of the total data set consisted of phytoplankton counts. 
About 74 species or species categories were identified in the tanks (Table 
24-3), but those that appeared five times or less were eliminated from the 
correspondence analysis (2). The remaining 54 species are identified in Table 
24-3 by a number in brackets following the species name. Generally only 3 to 
20 species were found at one time in any individual count. 
RESULTS 
When the microcosms were started in mid-August, 1976, the 
phytoplankton concentration in the Bay was decreasing after a very dense 
bloom (Figure 24-3). Concentrations continued to decrease until the end of 
August, and thereafter stayed low until the middle of November when another 
bloom began. The MERL microcosms followed a similar course, with the 
second bloom beginning somewhat earlier in some of the tanks than in the Bay. 
The values for chlorophyll a in water samples taken from the end of the GSO 
dock in all cases fell within the range of values plotted for the MERL 
microcosms. 
Figure 24-4 shows a plot of the number of species of phytoplankton 
counted in samples from the MERL microcosms, from the end of the dock and 
from three other stations. In nearly every case the number of species in samples 
from the dock lies within the range of total species reported for the tanks. 
Occasionally the values for the other three stations in the Bay lie outside the 
range in the tanks, but the variation appears random and the data sets do not 
appear to be separable. 
Indices of diversity and similarity were calculated using the phytoplankton 
species counts for the period noted. The Shannon index of diversity (Pielou 
1969), which takes account of the abundance of each species, was calculated 
for each of the tanks and the dock for each of the weekly samples (Table 
24-4). The mean value for the dock samples was higher than for the tank 
samples, indicating a somewhat greater phytoplankton diversity in the adjacent 
bay than in the tanks. 
365 
