Algal Identification

Harmful Algal Blooms

​​Harmful Algal Blooms in Maryland

Anabaena and Aphanizomenon

Among Maryland’s tidal waters, Anabaena species and Aphanizomenon flos-aquae are frequently found in freshwaters of the Potomac River and the upper Chesapeake Bay. Their greatest abundances are usually observed during the summer. These are filamentous cyanobacteria, capable of nitrogen fixation. Anabaena is one of four genera of bluegreen algae capable of producing neurotoxins along with Oscillatoria, Lyngbya and Aphanizomenon. Anabaena flos-aqua is a major producer of neurotoxins (Carmichael 1997 Advances in Botanical Research Vol 27:211-256). The best way to minimize animal poisonings by these species that produce cyanotoxins is to recognize you are in the area of a bloom and keep animals away from the waters that may be toxic. No human deaths have been directly associated with these cyanotoxins; however, they may cause skin irritations or nausea.

Farm animals and pets have been killed by the toxins when the animals ingested waters containing toxic blooms of one or a combination of these algal species. Such poisonings typically occur when heavy surface growths or scums of the cyanobacteria have accumulated near the shoreline and animals have easy access to toxic levels of cells (W.W. Carmichael). This type of toxin has been shown to persist in water for a week or more after the bloom has disappeared. Not all cyanobacteria blooms are toxic and even blooms caused by known toxin producers may not produce toxins or may produce toxins at undetectable levels.

It is not know what triggers toxin production. Recent studies have shown the probability that an individual bloom containing Anabaena, Microcystis, and/or Aphanizomenon will be toxic could be between 45 and 75% (Toxic Cyanobacteria Blooms; A Field/Laboratory Guide, Dr. M. A. Crayton). The presence of Anabaena in a water body can contribute to poor water quality because it can impart noxious odors and disagreeable tastes to the water.