RMBL researcher’s local work cracks code on didymo outbreaks

Phosphorous, not felt, responsible

For seven years he has sought the cause of widespread blooms of an algae known as didymo, or rock snot.
Now longtime Rocky Mountain Biological Laboratory researcher and Dartmouth College professor Brad Taylor finally has his culprit.

And the invasive outbreaks might have an origin closer to home than once believed, taking the unaware angler off the hook and placing the blame for the suffocating algae blooms on bigger environmental changes, according to a paper Taylor published in the journal BioScience.
Taylor reports the algae Didymosphenia geminata was likely always present in even our most pristine streams and rivers, turning from an insignificant diatom into an asphyxiating blanket of goop as a result of changing water chemistry and a changing climate.
Taylor started looking into the occurrence of large and unprecedented didymo blooms while at RMBL in the summer of 2007, a year after the blooms were first documented.
“The work at RMBL figured prominently in the BioScience paper,” Taylor says. Didymo cells are in many rivers around Crested Butte and Gunnison and have been for more than 50 years, based on the research at the RMBL.
According to Taylor, didymo blooms have been observed in the Taylor River, West Brush Creek, Cement Creek, East River, Oh-Be-Joyful below and above the wilderness area and Coal Creek, as well as some unnamed creeks and more.
But such large blooms are a new phenomenon, Taylor says. And for reasons still being researched, the didymo cells in Poverty, Slate, Rustlers, East Fork Crystal, and some other rivers don’t bloom in the way didymo has come to be known.
In his research plan on the RMBL website, Taylor says the second of two rounds of research, started in 2012, set out to answer four questions related to the didymo outbreaks.
First, he hoped to answer the question of whether or not timing and magnitude of runoff correlated with didymo outbreaks.
He wondered if the outbreaks could be related to the presence of beaver dams or occurred more in lake-fed streams.
What he found was an affirmative answer to his final question about the relationship between an outbreak and phosphorus levels in the water. Instead of the algae blooming in response to an abundance of nutrients in the water, didymo was extending its reach to gather what few nutrients were left.
Taylor doesn’t see any direct connection between low levels of phosphorous in the water and the abandoned mines in the area, since didymo occurs naturally in almost all streams, and blooms are being documented around the world. However, he said, the mats of didymo are trapping heavy metals that would otherwise flow freely downstream.
And while that might sound like a good thing, the heavy-metal-laden didymo will eventually flow downstream, Taylor says, potentially depositing the heavy metals en masse.
The mats also blanket brooding grounds for aquatic insects that provide the foundation of the food chain in small mountain streams and sustain fish populations.
“The blooms in rivers around Crested Butte can be substantial, though not as severe as I have seen in eastern U.S. rivers, or in Chile,” Taylor says. “The higher gradient limits the amount of biomass that can occur. Nonetheless, the amount of biomass is sufficient to change the invertebrate communities that the fish depend on for food.”
For most of the macro invertebrates in the affected streams, the didymo is a cloak of death, filling the voids in the streambed they exploit. But for a couple species of insects, the didymo is a boon.
One of those species benefiting from the didymo is the tubificid worm, which is a host for the parasite responsible for whirling disease, which also occurs naturally in fish populations throughout the United States.
But a greater abundance of tubificid worms could lead to more whirling disease and Taylor says the surrounding environment hasn’t been able to adapt to the rapid advance of didymo blooms.
“If the cause was simply introducing it, then we know the issues with that. However, didymo is the largest freshwater diatom and is likely a sentinel or canary in the coalmine of changes to our rivers,” Taylor says. “Concerted efforts that reduce human-induced changes to climate (e.g., earlier snowmelt and growing season) will probably attack the root cause of the didymo problem. Trying to kill it will have unintended consequences to fish and other algae. New Zealand has already tried this unsuccessfully.”
Taylor is currently working on another paper dealing with the impacts didymo is having on the food web in streams and the effect that is having on fish.