the microcosms. To some extent this may reflect the fact that the floating pair 
measurements and dye patches respond to the horizontal turbulent field and 
the gypsum and gas exchange are also influenced by vertical motion. The 
rotating plastic paddles appeared to add a lot of horizontal mixing energy to 
the tanks, but the vertical eddy diffusivity in the microcosms was lower than 
Hess (1976) calculated for Narragansett Bay (Table 25-1). 
While none of these measurements allows us to make a very convincing 
absolute comparison of turbulent energy in the microcosms with that of the 
bay, it does seem clear that the full paddle, half paddle, no paddle 
configuration provided quite different turbulent water regimes in the 
microcosms. Since the input of turbulent energy to Narragansett Bay must vary 
considerably during the tidal cycle and from day-to-day according to the 
winds, it seems reasonable that the natural pelagic community may well 
experience all of the turbulent conditions used in the microcosms. For 
comparative purposes, it is interesting to note that all of the methods used for 
measuring turbulence except the determination of neighbor diffusivity and 
energy flux (e) indicated that even the full paddle configuration was low 
relative to the bay. 
Response of the Plankton 
The first turbulence experiment was carried out during the month of April 
when water temperatures in the microcosms ranged from 8 to 12°C. The 
standing crop of phytoplankton as indicated by chi a increased dramatically in 
the one paddle and half paddle treatments compared with the unstirred tanks 
(Figure 25-1). A number of cursory analyses of water samples did not indicate 
that there were any major shifts in species composition in the different tanks. 
However, there were also marked and significant differences (Perez et al 1977) 
among treatments in the numbers of Acartia clausi, the dominant zooplankton 
in the microcosms and in the bay (Figure 25-2). While the rapid increase in 
phytoplankton in the one paddle tanks began almost immediately, Acartia 
nauplii did not really start to decline until after 10 days. In fact, a portion of 
the decline in nauplii between 10 and 16 days was simply due to growth of the 
animals into juveniles (Figure 25-2). An analysis of covariance was performed 
to establish whether the changes in phytoplankton density could be attributed 
to changes in zooplankton density the covariate, total grazers was found to be 
non-significant. This meant that the inverse relationship expressed by 
zooplankton and phytoplankton to water turbulence was due to a direct 
pattern than the indirect effect of water turbulence. In fact, an analysis of 
covariance on the mean algal standing crop during the experiment indicated 
that interactions with the total numbers of grazers in the microcosms (the 
covariate) was not significant (Perez et al 1977). It is possible, however, that 
the zooplankton present did not feed as effectively in the more turbulent 
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