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-scale turbulence on plankton at the organism scale. Normalized rates in response to turbulence were calculated in the present study for parameters related to growth,ingestion and energy expenditure. Growth rates are, in general, negatively affected by turbulence. Nevertheless, the data are highly biased towards a specific group of organisms, dinoflagellates, which could have 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 turbulent conditions; Although many experiments were conducted at very high levels of turbulence with respect to oceanic conditions, in most studies the Kolmogorov size microscale remained larger than the size of the planktonic organisms. Thus, organisms responded to turbulence or turbulence-derived stimuli below the Kolmogorov lengthscale. The ecological. relevance of interactions 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 show concentrations similar to those typical for large protozoa and algae (both within these organisms and between them and their potential predators). Characteristic time scales for different planktonic organisms are also explored in relation to the corresponding Kolmogorov time microscale. All planktonic organisms will experience fluctuations in the nutrient or food-particle fields over their lifetime. If other characteristic times are considered, such as the time between particle capture or nutrient uptake events, fluctuations may or may not be experienced over those times depending on the feeding mode and the turbulence intensity.