TURBULENT MIXING IN MARINE MICROCOSMS— 
SOME RELATIVE MEASURES AND ECOLOGICAL 
CONSEQUENCES 
Scott W. Nixon, Candace A. Oviatt and Betty A. Buckley 
Graduate School of Oceanography 
University of Rhode Island 
Kingston, R.l. 02881 
ABSTRACT 
The effect of turbulent water motion on pelagic organisms has seldom been 
studied. Nevertheless, a consideration of the theory of turbulent energy flux as 
well as the few bits of empirical data which do exist suggest that it may be a 
factor of some importance for marine plankton, and that turbulence may 
influence the growth, metabolism, and behavior of pelagic species as well as 
their spatial distribution. This paper reports the results of a series of turbulence 
experiments carried out over an annual cycle using small (150 1) laboratory 
microcosms designed as analogues of Narragansett Bay, R.L (U.S.A.). 
Turbulence levels in the mocrocosms and in the natural system were 
characterized using conventional (neighbor diffusivity, vertical eddy diffusivity, 
energy flux) parameters as well as a number of relative measures of water 
mixing (dye dissipation, CaSO^ dissolution rate, gas exchange coefficients). 
The response of phytoplankton and zooplankton populations to varying 
turbulence levels was dramatic during warmer months, but absent or unclear in 
winter. The results suggest that while phytoplankton may be stimulated by 
higher turbulence levels, at least in warmer water, the response of the 
zooplankton is quite the opposite during these periods. It is not clear if the 
response of the phytoplankton reflects a decline in grazing pressure or a real 
enhancement of growth. The problem is complex and deserves considerable 
further study both in the field and in the laboratory. 
INTRODUCTION 
“.. . diffusion is confusion. Only Maxwell’s Demon 
really knows what’s going on.” 
Akira Okubo (1971), 
Horizontal and Vertical Mixing in the Sea 
382 
