40 
CO 
UJ 
o 
UJ 
CL 
cn 30 
o 
h- 
0 - 1 - 1 - 1 - 1 — 
9/4 9/24 10/14 11/3 11/23 
Figure 24-4. Species of Phytoplankton 
NOTE: Solid lines indicate the range of the number of species of 
phytoplankton counted in samples from the MERL microcosms. The large 
opaque circles indicate the number of species from the dock samples. Three 
small dots connected by a vertical line indicate the number of phytoplankton 
species for three stations in upper Narragansett Bay (Durbin and Durbin, 
unpublished data). 
In order to assess the similarity in types of species in the community a 
similarity index (13) was calculated for each weekly data set. This index (S = 
2C/(A+B)) is a measure of the number of species in common between two 
samples. Calculations were made for each tank in comparison with the dock 
samples, and for some tanks in comparison with each other. Some of these 
indices are shown in Table 24-4. In general, the inter-tank similarity indices 
were about the same magnitude as the bay-tank indices. 
368 
