Phormidium is typically dark green, dark brown and sometimes even black. It captures and produces little bubbles of air by photosynthesis. Patches feel oil-like and filthy at the same time. Phormidium is a benthic cyanobacterium. This means that it often sticks to rocks or attaches itself to in-stream debris and weeds. It mainly forms microbial mats, sticking together. When the habitat is stirred by streams, wind, oxygen production, fishes foraging on the sand and plants, or feet from swimming people, patches of the microbial mats can come loose and float seperately.
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| Stereo photograph of a loose patch of Phormidium |
Phormidium is found in a wide range of water quality conditions, including relatively clean waters. It occurs naturally in waterways and is more likely to be present during the early spring and summer, than at any other time of the year. Phormidium typically forms thick scums on the surface, and may also develop foams at the water's edge.
The absence of signs in the field does not necessarily mean that the waters are safe to swim in as blooms can occur very rapidly. Phormidium can produce toxins which may prove fatal to dogs and people can become quite ill: asthma, eye irritations, rashes, blistering around the mouth and nose, and gastro-intestinal disorders, including abdominal pain, cramps, and diarrhoea.
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| Seperate filaments of Phormidium sp |
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| Extensive bloom of Phormidium sp and Oscillatoria sp Both photographs taken with Olympus IX70 cellSens Dimension 600x and 200x immersion oil. Photographs: Marta Demarteau/Aquon |
Some Phormidium species are known to produce neurotoxins, while other species are believed to be quite harmless. Due to the lack of knowledge about benthic cyanobacteria and toxin production, it's very difficult to determine toxicity of particular species.
However, the potential of toxin-producing cyanobacteria does mean: the higher the concentration of cyanobacteria toxins and the longer the contact with the water, the more severe the symptoms are likely to be. This may sound very alarming, though it's not sure yet that all Phormidium species produce toxins, and it depends on the conditions at stake. Only tests of samples can conclude if toxins are produced. Swimming waters are therefore monitored by (1) taking samples, (2) screening the samples to conclude if Phormidium is present, and (3) if needed, a toxin analysis.
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| Working in the field... Photograph: Henri Rovers/Aquon |
Baker PD, Steffensen DA, Humpage AR, Nicholson BC, Falconer IR, Lanthois B, Fergusson KM & Saint CP (2001), Preliminary evidence of toxicity associated with the benthic cyanobacterium Phormidium in South Australia, Environ Toxicol 16: 506–511.
Environment Canterbury Regional Council, Dangers of toxic algae, August 2009, updated October 2009, For the link to this news article, click here.
Komarek J (2006), Cyanobacterial Taxonomy: Current Problems and Prospects for the Integration of Traditional and Molecular Approaches, Algae Volume 21(4): 349-375.
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Otago Daily Times, Toxic algae blamed for death of two dogs, feb. 2010 For the link to this news article, click here.
Rijkswaterstaat, Ministerie van Infrastructuur en Milieu (2011), Handreiking blauwwiermatten, internal newsletter Rijkswaterdienst Lelystad 1-7 (only used for background information, not for publication as promised).
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