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 weiglied. 



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, fromi the end of the dock and 

 from three other stations. In nearly every case the number of species in samples 

 from the dock Hes Mdthin the range of total species reported for the tanks. 

 Occasionally the values for the other three stations in the Bay He 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. 



367 



