Analysis tool for swimming marine microorganisms using acoustic tweezer.

Phytoplankton, as primary producers through photosynthesis, are fundamental to marine ecosystems. However, their rapid proliferation in coastal regions has increasingly led to harmful algal blooms (HABs), commonly known as red tides, which pose significant environmental, economic, and health risks. A deeper understanding of phytoplankton dynamics, particularly their movement patterns such as diel vertical migration (DVM), is essential for effective monitoring and prevention of HABs. Traditional measurement techniques, including acoustic Doppler current profiling (ADCP) and acoustic backscatter, are limited by spatial and temporal resolution constraints, making it challenging to capture fine-scale phytoplankton behavior. In this study, we introduce a novel application of single-beam acoustic tweezer (SBAT), which employs a single concave bulk ultrasonic transducer to generate a focused acoustic beam, to confine and track the swimming behavior of Cochlodinium polykrikoides (C. polykrikoides), a representative HABs-forming species. SBAT provides precise, non-invasive manipulation and clustering of individual cells, offering a powerful alternative to conventional methods. Our findings highlight the versatility of SBAT in studying phytoplankton motility and environmental interactions, paving the way for improved HABs management strategies.