Phycocyanin measurement instruments

Cyanobacteria (or blue-green algae) are photosynthetic bacteria that occur naturally in surface waters. Under certain conditions (high light, nutrient levels (N and P), warmer temperatures) cyanobacteria can multiply rapidly forming a bloom. Some Cyanobacteria are toxin-producing and the term harmful algal bloom (HAB) applies. The cyanotoxins (e.g. microcystins) produced by the algae can pose health risks to humans and animals.

Some cyanobacteria use gas-filled cavities to float to the surface (where they may be visible as blue-green “scum”) or to different levels below it. Others are benthic – living on bottom sediments, and others may be dispersed through the water column. Turbulence is capable of mixing the three types.  Although not all cyanobacteria produce cyanotoxins, these may be present both before and after cyanobacteria are observed.

The EU Bathing Waters Directive requires monitoring for blue-green algae blooms. Surface waters used for drinking water or recreation should therefore be monitored to permit detection of blooms before they become visible or dangerous, and monitoring at various depths or via profiling is therefore desirable.

Testing for the actual toxins is possible, though requires discrete sampling and expensive laboratory equipment and cannot provide real-time data. Phycocyanin fluorescence can be used for real-time, sample-free monitoring of cyanobacteria to indicate trends. However some caveats should be born in mind: the fluorometer output is only a proxy for HAB concentration, very different results can be returned from fluorometers made by different manufacturers in the same location (optics/filters), phycocyanin production rates are strain-specific, light intensity and nitrogen availability also have a significant impact on phycocyanin content, and turbidity can affect the readings.