Plankton species live in a turbulent flow and are fully adapted to it. They have specific responses related to turbulence characteristics and intensities, such as swimming behavior or shape. There exist a turbulence intensity range to which planktonic life adaptation is optimal.
In the field, many parameters are interacting due to the complexity of ecosystems and it is difficult to precisely determine the role of each parameter. This is why controlled conditions in experiments performed in the laboratory can help to better understand these systems, such as turbulence systems. The way to connect experimental studies with field studies is to control the Reynolds number of the flow, which characterizes the turbulence intensity.
Here we present some results using different plankton species. In the Agiturb system, the turbulent flow is produced using four contra-rotating agitators that are place under a cubic tank. Different values of the rotation rate were chosen to reach different turbulence levels, characterized by an estimated microscale Reynolds number R_λ going from 130 to 360.
The first experiment is a record, using a high speed camera, of copepods trajectories (Acartia tonsa), at different turbulent intensities. In order to emphasize the swimming contribution to the copepod dynamics, the PDFs of alive and dead copepods are compared, for velocities as well as acceleration magnitudes. An optimal Reynolds number is found in both cases.
The second experiment is a study of the effects of turbulence on two species of the chain forming diatom Pseudo-nitzschia which can be toxic under certain conditions. We present here some results on the growth of these microalgae their chain formation and associated bacteria, in relation with the turbulence intensity. As for copepods, a dome shape was obtained and optimal Reynolds numbers were found.
Here a review of the results obtained with the AGITURB system is proposed, based on the works done with colleagues authors of the two papers:
• Le Quiniou, C., Schmitt, F.G., E. Calzavarini, S. Souissi, Y. Huang, Copepod swimming activity and turbulence intensity: study in the Agiturb turbulence generator system, EPJ Plus, 137, 250, 2022.  https://doi.org/10.1140/epjp/s13360-022-02455-7
Maire, Y., F.G. Schmitt, K. Kormas, S. Vasileiadis, A. Caruana, D.-I. Skouroliakou, V. Bampouris, L. Courcot, F. Hervé, M. Courvoisier, U. Christaki, Effects of turbulence on diatoms of the genus Pseudo-nitzschia spp. And associated bacteria, FEMS Microbiology Ecology, 100, fiae094, 2024. https://doi.org/10.1093/femsec/fiae094

Turbulence,plankton,phytoplankton,zooplankton,Laboratory Experiment