Insight into red-pigmented algal bloom by CytoSense

17.04.2020  by  Tina Silovic


Figure 1: Sample of water taken at Geestmerambacht

Figure 2: Cytogram showing P.rubescens cluster, together with a collection of images of the defined cluster

Figure 3: Sample length of defined cluster of P. rubescens

Figure 4: Pulse shape profile and corresponding photo of P. rubescens

Following the recent news about an early harmful algal bloom (HAB)* in a lake in the recreational park Geestmerambacht we decided to pick up a sample and analyse it with our CytoSense. The sample we took from the dense surface layer had nice purple colour (Fig. 1), from the red-pigmented algae (Planktothrix rubescens** as confirmed on Twitter by Rijkswaterstaat’s taxonomist), known as the "Burgundy-blood phenomenon."The CytoSense analysis showed a huge amount of filaments (trichomes) of the blooming cells,  forming one cluster (Fig. 2). The sample contained 6.5*10^4 of such trichomes per milliliter, with an average length of 315 µm (Fig. 3).

Aside from images and counts of the blooming algae, the CytoSense analysis provides a scan of optical properties for each particle.

This scan (Fig. 4) presented above the corresponding photo, shows light scattering and fluorescence measured along the length of each particle.  In this case the filaments all have a large, similar amount of yellow and orange fluorescence, associated with the accessory pigments Phycoerythrin (PE) and Phycocyanins (PC).  Some Planktothrix types can be classified separately from each other according to the PE:PC ratio, Komarek & Komarkova, 2004), in terms of values (Fig. 4) or ratios.


Planktothrix species have no heterocyst and no akinetes, but are unique because they are planktonic, solitary trichomes and have gas vacuoles.  Most trichomes showed gas vacuoles over their whole length. In Fig. 4 we show a peculiar one, where you can clearly see parts of the cells having internal gas vacuoles (middle section). Gas vacuoles caused strong sideward light scatter (SWS)(proxy for a cell structure) peeking up at parts where gas vacuoles are present. The particle scan also shows there is an equal distribution of pigments over the length of the trichome, unaffected by the gas vacuoles.  The photo clearly shows the presence of the gas vacuoles within the cell: black with gas, white without gas.    

Since these algae can produce toxins, it is important to monitor such waters and alert the community in order to prevent animals or people having health issues. The CytoSense is a great tool to monitor such waters giving all the information it produces. Moreover, it has a great ability to run autonomously, analyzing samples and provide online alerts on changes in the algal community.


*An algal overgrowth is referred to as an "algal bloom." Harmful algal blooms (HABs) refer to blooms with the potential to harm human health or aquatic ecosystems.
**Planktothrix is a genus of filamentous cyanobacteria (often called blue-green algae).