(BV / 05-10-09) A microscopic diatomea, Didymosphenia geminata has become a headache for those responsible for the recently colonized rivers. Very difficult to eradicate, as all invasive species, it causes serious changes in the river ecosystem and can clog pipes and hydraulic installations.

There is growing concern about the spread and adverse environmental effects of the algae Didymosphenia geminata, commonly known as “didymo”, or “rock snot”.

Worldwide considered as one of the most disturbing freshwater invasive species, D. geminata is a microscopic organism belonging to the class of Diatoms, unicellular algae bearing a siliceous shell, which forms colonies that attach to any hard substrate in rivers, lakes and reservoirs.

Although it is native to the circumboreal region, there have been massive growths of this species in rivers throughout North America, Europe and New Zealand, where it currently continues to extend its range. The situation is particularly critical in New Zealand and the Pacific Northwest, with much of its river channel affected by massive infestations.

Until recent years, the literature related to D. geminata as a species restricted to pristine habitats, poor in nutrients and low temperatures, but it is currently in lower latitudes and altitudes, where it has adopted a more aggressive ecological behaviour.

There are evidences that the ecological profile of this species has changed over recent decades. Numerous studies suggest that their environmental range might be much broader than considered until now, particularly its tolerance of nutrient concentration and temperature, since it is lately appearing in entropic rivers of warm climate.

It has also been found that this diatom thrives especially in regulated channels and, in fact, it can support varying flow much stronger than other algae. Worse, during the rise in river level some colonies come off and contribute to the dispersion of the species.

In any case, it is still very little what is known about the ecological preferences of this species and the factors that triggered the massive growth. It has been suggested that increased UV radiation may promote their growth, but other authors point to a genetic variant which broader ecological range is responsible for the current infestations.