Thick, wooly carpets of "rock snot" algae proliferating across eastern Canada may be driven by climate change, according to a new study.

Previously, many water managers in the region had believed that the algae blooms of the diatom Didymosphenia geminata -- which resemble blobs of wet toilet paper or shag rugs -- resulted from an invasive species problem starting in the mid-2000s that could be fixed by regular washing of fishing gear and other sanitation measures.

But in the new study, a team of scientists found that the diatom, informally known as didymo or rock snot because of its globular appearance, dwelled in eastern Canada in the 1970s, even though it was not detected then.

Since the algal species is native to eastern Canada, its recent blooms and rapid proliferation in rivers since 2006 -- which have angered anglers looking for pristine waters -- have been caused by an environmental trigger, with climate change a likely culprit, said Michelle Lavery, a master's degree student at the Canadian Rivers Institute and lead author of the research, published in theCanadian Journal of Fisheries and Aquatic Sciences.

The spongy algae has always been there, just in unnoticeable numbers, she said. The study corroborates historical reports of didymo's presence as far back as the 1800s, she said.

"We suspect that climate change is favoring this species in several ways," Lavery said. The climate link is a hypothesis, and much more research is needed to determine a cause, but the effects of warming seem to favor the species, she said.

For one, didymo likes stable river flows, so it is not scoured from its rocky home at river bottoms.

With documented warmer air temperatures in eastern Canada since the 1970s, there has been a trend of earlier ice melting and less ice in general, explained Lavery. That, in turn, lessens the surge of ice into the river and prevents water surges from ripping the algae off their foundations. It creates a more stable thaw season, she said.

"Instead of having to start over every summer, they can build on themselves and get bigger and bigger," she said.

The research team -- which included scientists from Queen's University, Brock University and Institut National de la Recherche Scientifique -- examined meterlong sediment cores from two Quebec lakes near affected rivers. They also examined air temperature and ice records going back more than a century. The temperature records showed a warming spike after the 1970s, and the ice records documented that river ice is breaking up about nine days earlier now than last century.

One of the cores showed the appearance of didymo in the 1970s, before its later blooming growth. The second core showed a shift in other diatoms in the second lake around the same time in favor of species that thrive in warming temperatures. "The second core puts didymo in a climate context," Lavery said.

Also, the 2006 blooms occurred during the "decade with the warmest mean annual temperatures and the earliest ice-off dates," the study said.

The algal blooms were first reported officially in eastern Canada in the Gaspesie region of Quebec in 2006 and later appeared in more than 25 nearby river ecosystems, according to the study. The diatoms also have proliferated in places like New Zealand and the Delaware River. Vermont, Maryland and other states banned felt-soled waders in 2011 out of fear of spread.

Fishermen unhappy, scientists baffled
The algal blooms are despised by many anglers in eastern Canada, and many have poured money into research. The new study, for example, was partially funded by the Atlantic Salmon Conservation Foundation, along with the Natural Sciences and Engineering Research Council of Canada.

In addition to being unattractive and disruptive to the pristine river fishing experience, the algal blooms could affect salmon, said Lavery. With more algae, there are more bugs available for salmon to eat, allowing the fish to forage more on the bottom.

"It could be good for them, or it could be bad for them, or anywhere in between," said Lavery of the fish.

Three didymo experts not involved in the study agreed that climate change possibly is playing a role with didymo, although the degree of the link is uncertain.

"There's still a lot of mystery," said Robert Pillsbury, an associate professor at the University of Wisconsin, Oshkosh.

An alternative theory is that increases in abundance of nitrogen in river water -- perhaps from carried dust from farming or industrial operations -- are also driving the blooms, said Pillsbury. Unlike other types of algae, didymo does not thrive with high levels of phosphorus or nutrients from fertilizer runoff, but it does prefer higher amounts of relative nitrogen.

In an upcoming paper, Max Bothwell, a scientist at Environment Canada, proposed that climate change is one of four factors -- along with atmospheric deposition of nitrogen from fossil fuel burning -- boosting the blooms. He said in an email that he has been presenting the likely climate connection to dozens of universities in Canada and the United States before the paper's publication.

P.V. Sundareshwar, an associate professor at South Dakota School of Mines and Technology, said he also suspects that nitrogen is at play, even though there also may be a climate change contribution. In earlier studies, some didymo blooms were associated with drought, for example. But the climate factors likely were working in tandem with something else, like nitrogen, he said.

"I'm not convinced climate change is the main sole driver," said Sundareshwar.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500