A widely used technique for cell harvesting is crossflow microfiltration. The relative fragility of microalgae requires choosing a suitable pumping system. Tetraselmis suecica, which is a very mobile alga, is an interesting model for this study. The extent of damage observed in various pumps was measured as a function of the number of passes of the algal suspension through the pumps in a closed loop. A loss of microalgal motility could occur with either centrifugal or rotary vane positive displacement pumps. On the contrary, electronic microscope observation revealed that, during concentration using an eccentric rotor pump or a peristaltic pump, microalgae were not damaged.