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.I. 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. Tliis 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.I. (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 

 enliancement 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." 



AkiraOkubo(1971), 



Horizontal and Vertical Mixing in the Sea 



384 



