20 



15 







o- 



— BAY 

 — o NO PADDLE 

 — c 1/2 PADDLE 

 — • 1 PADDLE 



1 



1 



25 



30 



5 10 15 20 



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 tanl<s. 



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 1 5 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. Tliis 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 v/ith a full paddle, though the effect was not as 

 dramatic as in the earlier runs (Figure 25-3). The response to hght 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 25-4). 



396 



