A special camera for the tiny plankton

It looks like a black box, 70 cm large, with a funnel on top, connected to a computer screen. The device is called a FlowCAM and it’s one of the scientific instruments on Tara. FlowCAM inventor, Mike Sieracki embarked for 3 weeks from Malta to Dubrovnik to install the machine, organize the protocols and teach scientists how to use it.

Mike works for the Bigelow laboratory in Maine on the east coast of the United States. In 1982 it was the first oceanographic research institute equipped with a flow cytometer. This machine can detect and quantify tiny organisms such as viruses or bacteria in a high pressure water flow. During an oceanographic campaign Mike used a « video plankton recorder » an instrument which take pictures of small jellyfishes, larvae, and copepods.  All are important components of planktonic food webs.

« At that time, there was a gap between the very small organisms the cytometer could detect and the big ones seen by the recorder » notes our ingenious researcher.  These organisms are mainly protists, unicellular organisms with a nucleus. Some get their energy from photosynthesis, some feed on tiny particles, and some do both. They can be chubby, elongated, shaped like a leaf, studded with small tips or look like horned tripods…the diversity of forms among protists is amazing.

So Mike imagined a machine that could take a picture and measure the size of small planktonic creatures in real-time. A 200 ml seawater sample is poured into a funnel and sucked down by a pump. The FlowCAM’s main attribute is a laser used to detect two pigments: chlorophyll and phycoerythrin which are present in red algae and some cyanobacteria. When an organism containing those pigments crosses the laser beam, it triggers a flash and the machine instantaneously takes a picture.

FlowCAM can distinguish and sort individuals and on the basis of their size and their aspect : large or small, more round or more elongated. In 200 ml of water there can be 1 to 10 thousands cells. Mike selects an area on the screen: « small and plump for example »… an image of black and white portraits appear: « mainly diatoms… ». When the picture is good it’s even possible to see the very refined silicate structures that microscopic protists produce.

 150 Flowcams have been sold worldwide, to Spain, South Korea, Norway, England… Tara purchased one of them. « It’s an automated instrument well adapted for the boat because vibrations don’t bother its operation: no need to mobilize a scientist»

Sacha Bollet