Planktonic micro-organisms in a microfluidic environment

Planktonic micro-organisms play an important role in marine ecology, fishery, and the ocean carbon cycle. As the foundation of the oceanic food chain, phytoplankton and zooplankton form a complex food web, and their trophic interaction is vital to the prosperity of other marine life. In this talk, I will demonstrate how microfluidic devices can be employed to gain a better understanding of marine ecosystem in a single-cell level.

Focusing on studying the locomotion of plankton K. veneficum (CCMP426), we design a microcavity device to investigate the effects of different microflow conditions: stationary f/2-Si medium, steady flow, and oscillatory flow.

After measuring the local flow field, we are able to determine the absolute and relative velocities of individual plankton cells, from which their rheotaxis can be derived. The probability density function, the expected value and the standard deviation are calculated in order to statistically represent the locomotion of the planktonic community.

The experimental results show that when the plankton reside in stationary and homogeneous nutrient medium, the swimming velocity and the acceleration are 52.7±43.5 m s-1 and 878±820 m s-2, respectively. In addition, K. veneficum is capable of maneuvering in a flow speed up to 150 m s-1. Once the current is too strong, their locomotion is dominated by the flow. Under the condition of oscillatory flow, K. veneficum exhibits positive rheotaxis.

In the strong flow field region, planktonic cells can not directly cross the streamlines. Rather, they tend to cut through streamlines with small angle in order to reach the weak flow field region. The outcome of this study helps us clarify the interaction between the behavior of plankton and the microfluidic environment.