Didymo is a thick, slippery algae nicknamed "rock snot" for reasons obvious to anyone who has seen or touched it. The algae is a concern for fish populations such as Atlantic salmon, as it lines river bottoms, hiding food and making it more difficult for some species to forage.
"It's like a really bad seventies shag carpet," said University of New Brunswick graduate student Michelle Lavery, the lead author on a report done in collaboration with researchers at Queens University, Brock University, and l'Institut national de la recherche scientifique (INRS). The study was published in the Canadian Journal of Fisheries and Aquatic Sciences.
Didymo was not known in eastern Canada until it suddenly appeared in New Brunswick and Quebec rivers and lakes in 2006, leading many to think it had been introduced from somewhere else. It has also been observed east of the Rockies in Alberta and in British Columbia, where its appearance was thought to be linked to the use of felt-soled fishing boots. Such boots have been banned in some U.S. states over concerns that they might be transferring didymo.
The new research reveals the slimy, porous algae that has been reshaping eastern Canadian rivers is not the new kid on the block everyone thought it was.
"We found it in dated sediments from 1970," says Lavery. "And it's also been reported in historical reports from 1910 to 1896 even."
Researchers believe warming temperatures brought didymo back to prominence in recent years. Some of the evidence for this comes from layers of sediment from the bottom of a lake in the region that provided information about how the populations of different kinds of algae changed over time.
"We've seen a trend in the fossilized algae community from that lake that shows a very strong trend towards increased temperatures and the associated lake effects that come with increased temperatures," said Lavery.
People are still being advised to make efforts to keep didymo from spreading by washing waders and fishing gear when moving from river to river.
The study was funded by the Atlantic Salmon Conservation Foundation and the Natural Sciences and Engineering Research Council of Canada.