20 
t 
15 
!_I 
O' 
0 
DAYS AFTER 5 APRIL 
Figure 25-1. Chlorophyll Concentrations (In Vivo Fluorescence) 
in the Microcosms and in the Lower West Passage of Narragansett 
Bay During the First Turbulence Experiment Begun April 5, 1976. 
NOTE: Data points are the mean of duplicate tanks. 
tanks. It is striking that the zooplankton standing crop with one paddle was 
» 
very similar to that found during the same period in the bay, while the 
phytoplankton populations in those tanks reached levels 3 times greater than 
found in the bay with similar zooplankton numbers. Conversely, the low and 
relatively constant phytoplankton standing crops in the unstirred microcosms 
were almost identical to that found in the bay, but much larger zooplankton 
populations were sustained, at least for 15 days, in the microcosms. It may be 
that the plankton in the microcosms escaped a significant grazing and/or 
predation pressure that was important in setting the standing crop maintained 
in the field. This experiment was repeated during May with virtually the same 
results. 
The next turbulence experiment was not begun until December, when water 
temperatures ranged from 1 to 6°C and the standing crops of phytoplankton 
were low. The experiment was designed to explore not only the effect of 
turbulence, but also the interactions of turbulence with light and nutrient 
enrichment. Again, the standing crop of phytoplankton was significantly (0.05 
level) higher in tanks mixed with a full paddle, though the effect was not as 
dramatic as in the earlier runs (Figure 25-3). The response to light was not 
significant at the 0.05 level but was significant at the 0.10 level. The response 
to turbulence was highly significant (greater than the 0.01 level) (Figure 254). 
394 
