This study concerns the effects of small-scale turbulence and its small scale shear on the growth rate, cell division, cell size distribution, and cell morphology of marine dinoflagellates. The aspect of turbulence most important to phytoplankton is the local shear, or rate-of-strain which varies over three orders of magnitude in the ocean. The rate-of-strain in turn, determines the relative velocities for separation distances smaller than the Kolmogoroff scale, and phytoplankton are smaller than this scale in the ocean. Based on previous results, the working hypothesis of this study will be that differences in species composition of experimental cultures can be brought about by the inhibitory effects of high turbulence. In controlled laboratory experiments, turbulence and shear levels will be computed for the linear velocity profile and small shears in laminar flow, or estimated from established turbulence formulae for higher shear rates. The estimates will be confirmed by hot wire anemometer and microconductivity probe measurements. Constant shear, or variable shear under microcomputer control will be produced between rotating cylinders over a wide range of Reynolds numbers, with or without time variation. Daily measurements of chlorophyll fluorescence and cell numbers will be made to asses culture growth rates. Changes in cell size distributions and cell division rates will also be measured due to turbulence and shear and examine the cells microscopically to assess morphological changes. The threshold turbulence and shear levels which result in effects on these parameters will be ascertained. The microscopic plants called phytoplankton that are responsible for most marine biological production must contend with unique environmental conditions. For example although (like their terrestrial counterparts) phytoplankton require light and nutrients, these small and in some cases delicate cells are subject to the small scale physical forces of the surrounding water, which is 1000 times more viscous than air. Such small scale turbulence is generated in the sea by wind, tidal, internal wave, and current motions. This work is a novel collaboration between a phytoplankton biologist and a physicist to examine the effect of these forces on the growth and selected other features of dinoflagellates, a type of phytoplankton that is suspected to be susceptible to turbulence. This laboratory study will be carried out in a specially built apparatus in which the physical turbulence the phytoplankton are exposed to can be carefully controlled. Although the work is a pilot project, the interdisciplinary nature of the work by two very capable scientists has generated great interest in the potential findings that may have broad implications beyond dinoflagellates.
