Effects of turbulence on plankton: an overview of experimental evidence and some theoretical considerations

From the literature we obtained experimental data on the effects of small-s cale turbulence on plankton at the organism scale. Normalized rates in resp onse to turbulence were calculated in the present study for parameters rela ted to growth,ingestion and energy expenditure. Growth rates are, in genera l, negatively affected by turbulence. Nevertheless, the data are highly bia sed towards a specific group of organisms, dinoflagellates, which could hav e peculiar physiological impediments under turbulence. Ingestion rates seem to be increased by turbulence, especially at low and intermediate levels. The few data available on energy expenditure indicate increases under turbu lent conditions; Although many experiments were conducted at very high leve ls of turbulence with respect to oceanic conditions, in most studies the Ko lmogorov size microscale remained larger than the size of the planktonic or ganisms. Thus, organisms responded to turbulence or turbulence-derived stim uli below the Kolmogorov lengthscale. The ecological. relevance of interact ions between turbulence and other size-related parameters, such as reactive distances, mean free paths and Batchelor microscales, are mentioned mainly in terms of predation, nutrient uptake and competition. Specifically, mean free paths seem relevant to determine encounter rates for organisms that s how concentrations similar to those typical for large protozoa and algae (b oth within these organisms and between them and their potential predators). Characteristic time scales for different planktonic organisms are also exp lored in relation to the corresponding Kolmogorov time microscale. All plan ktonic organisms will experience fluctuations in the nutrient or food-parti cle fields over their lifetime. If other characteristic times are considere d, such as the time between particle capture or nutrient uptake events, flu ctuations may or may not be experienced over those times depending on the f eeding mode and the turbulence intensity.