报告摘要：

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, shape or density regulations. It is generally believed that there exist a turbulence intensity range to which planktonic life adaptation is optimal. Turbulence systems in the laboratory are useful to perform controlled experiments with different zooplankton and phytoplankton species.

Here we present the Agiturb turbulence generation system and results using different plankton species. In the Agiturb system (Le Quiniou et al., 2022), the turbulent flow is produced using four contra-rotating agitators that are place under a cubic tank. The model for such flow is the “four-roll mill” proposed by G.I. Taylor in 1934 to generate a statistically stationary, spatially inhomogeneous flow. In our experiment, the injection of the energy in the flow is produced by 4 stirring bars activated by 4 magnetic stirrers situated at symmetric positions. For each experiment, the magnitude of the rotation rate of each agitator was identical, with two agitators rotating clockwise and two anti-clockwise. 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.

We present the result of two different experiments: the first one is a record, using a high speed camera in the infrared, of copepods trajectories, at different turbulent intensities. The studied copepods belong to the species Acartia tonsa and have a body length of approximately 0.6 mm, and active swimming activities. 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 phytoplankton species of the chain forming diatom Pseudo-nitzschia which can be toxic under certain conditions: P. multiseries (length: 68-140 µm, width: 3.5-5 µm) and P. fraudulenta (length: 73-117 µm, width: 5-6 µm). We present results on the growth of these microalgae, their chain formation, associated bacterial communities, domoic acid production, Chla content in relation with the turbulence intensity in the tank. As for copepods, a dome shape is obtained for many of these properties and optimal Reynolds numbers are found (Maire et al. 2024).

个人介绍：

Francois G Schmitt教授现为法国国家科学研究中心(CNRS)研究教授，法国滨海大学(ULCO)、里尔大学教授，2006年至2019年任法国海洋与地球科学实验室(Laboratory of Oceanology and Geosciences)主任，2015-2019年任欧洲地球科学联名非线性科学部副主席，2020年至今任主席。Schmitt教授长期从事海洋环境中的湍流、生物化学多尺度动力学过程研究。