CytoBuoy: a step forward towards using flow cytometry in operational oceanography

While the performance of biological sensors in real time monitoring networks is limited to bulk values like chlorophyll fluorescence, in practice the implementation of automated phytoplankton taxonomy remains a remote option. Aiming to reduce this gap we developed a flow cytometer called CytoBuoy for autonomous in situ operation, for instance in a moored buoy with wireless data transfer. Although not comparable to microscopy, flow cytometers detect and count particles allowing a limited level of particle characterization based on the light scatter and fluorescence properties of the individual particles. CytoBuoy analyses a large size range of particles, typical for marine coastal zones and fresh waters. The `field´ design implies a tradeoff between the accuracy and versatility of laboratory flow cytometers and the qualities needed for trouble free autonomous operation in situ. The optics and electronics however were designed for maximal reflection of the particle morphology in the measured signals. Whereas standard cytometers reduce these to single peak or area `listmode´ numbers, the signal courses are preserved fully by CytoBuoy and transferred to the computer as raw data, which allows more extended morphological analysis. Extended field tests will have to show how the system holds in various environments and weather conditions.