Tracking of algal cells: case study of swimming speed of cold-adapted dinoflagellates

Swimming is a fundamental trait of many protists and optimizes growth and survival. We present an easy to use set-up for filming algal cells using Apocalathium aciculiferum and Borghiella dodgei as case studies; both dinoflagellates are model organisms of psychrophilic dinoflagellates. We filmed at low temperature (4.5°C) using a digital camera directly connected to a microscope and used open-source software to track their movement. We encountered several technical issues that were solved by using specific software settings (scaling, grey scale of images, restrictive particle recognition), and thus we obtained unbiased speed estimates. Borghiella dodgei showed a faster (minimum = 80, maximum = 255, median = 141 µm s −1 ) swimming speed than A. aciculiferum (minimum = 29, maximum = 134, median = 85 µm s −1 ). We linked differences in swimming speed to the dinoflagellates’ environmental niche, and suggested that B. dodgei is more adapted to turbulent spring conditions than A. aciculiferum , occurring under ice. The use of a generic digital camera and open-source software makes filming and tracking of plankton movement very affordable. We provided code and detailed instructions to disseminate this type of movement analysis of plankton.