How phytoplankton aggregation drives turbulence and promotes ecological cooperation

When microorganisms swim as a group, their collective motions create flow patterns in their surrounding fluid, a process known as bioconvection. This reshapes nutrient distributions and impacts ecological dynamics in aquatic environments.

Phytoplankton, on the other hand, have long been believed to move passively with their surrounding flow, not playing a significant role of their own. However, Zhu et al. studied the mechanics of the bioconvection process for the marine phytoplankton Effrenium voratum and uncovered a more active process.

Using high-resolution video microscopy and controlled laboratory experiments, the team observed that once the cell concentration exceeds a critical threshold, the collective upward motion of E. voratum populations, combined with gravity’s downward pull, results in bioconvection. This process creates plume structures that accelerate the movement of the surrounding fluids and the nutrients they carry, similar to turbulence. These flows enhance vertical mixing of the fluids and their constituents, effectively increasing nutrient availability across different depths and benefiting even non-aggregating cells — a form of ecological cooperation among phytoplankton.

“This process fundamentally alters the miscroscale environment experienced by phytoplankton,” said author Quan-Xing Liu. “This redistribution facilitates nutrient access even for non-swimming or weakly motile cells, representing a form of ecological cooperation.”

The authors also quantified the energy spectra of the induced flows, revealing an a hallmark of turbulence. A coupled numerical model successfully reproduced key features of the experimental observations, including plume formation, cell density distribution, and enhanced vertical transport.

Liu says the group’s current focus is to understand how body shape, swimming strategies, and species-specific behaviors influence spatial organization in bioconvective flows. They hope to uncover how these physical-biological interactions shape microbial coexistence and biodiversity in marine systems.

Source: “Turbulent mixing through aggregation-driven bioconvection in Effrenium voratum,” by Zheng Zhu, Xiaoqing He, Houshuo Jiang, and Quan-Xing Liu, Physics of Fluids (2025). The article can be accessed at https://doi.org/10.1063/5.0268880 .