A recent study suggests that glacier reatreat may contribute to spread of a noxious invasive algae species in Chile. The particular species is a kind of algae, Didymosphenia geminata, commonly called “didymo.” Since this microscopic organism, a kind of planktom, forms thick dense mats that coat rocks, it is also known as “rock snot.”

Vivián Montecino and her co-authors report on the spread of this species in a paper published earlier this year in the journal Science of The Total Environment. They discuss a recent bloom of this species that occurred in 13 river basins in Chile between 2010 to 2015, extending over 1800 kilometers in central and southern Chile. Didymo has been found around the world. The dense algae mats are a problem because they are unpleasant, creating problems for tourism and sport fishing. Moreover, they interfere with local ecology, since they cover rocks that are the habitat for larve of aquatic insects, disrupting aquatic food webs.

Didymo is native to the northern hemisphere, but recently has extended its range to the southern hemisphere, including Australia, New Zealand, Argentina and, as this study shows, Chile. It spreads rapidly and has proved very difficult to eradicate.

The researchers gathered water samples at over 300 sites between 2010 and 2015 in 13 river basins, assessing physical and chemical characteristics of the samples and checking for the presence of didymo. They found that in Chile, as in other regions, it is concentrated at site with low water temperatures and in streams that have low concentrations of phosphorus. They noted the presence in didymo in nearly all the rivers in Chile with these characteristics, suggesting that it may not continue to spread in the future. They note that didymo took a similar amount of time, about 6 years, to spread across the South Island of New Zealand, reaching its full extent in that time.

The authors note that the spread of didymo to the south may be associated with glacier retreat. They comment that glacier retreat in the watershed of the Baker River is associated with increased stream flow in the summer, leading to a lowering of phosphorus concentrations which favor the species. The Baker River drains the rapidly shrinking Northern Patagonian Icefield.

This research demonstrates the complex consequences of glacier retreat. It seems paradoxical that the dilution of nutrients such as phosphorus associated with increased stream flow could favor invasive species, but dense mats of rock snot that cover the rocks along stretches of the Baker River demonstrate this association. As glaciers change, the ecosystems in the rivers fed by their meltwater also change, often for the worse.