|Didymo found beside the Mararoa River in New Zealand.|
(Lyngbye) M. Schmidt, 1899
Didymosphenia geminata, commonly known as didymo or rock snot, is a species of diatom that produces nuisance growths in freshwater rivers and streams with consistently cold water temperatures and low nutrient levels. It is native to the northern hemisphere, and considered an invasive species in Australia, Argentina, New Zealand, and Chile. Even within its native range, it has taken on invasive characteristics since the 1980s. It is not considered a significant human health risk, but it can affect stream habitats and sources of food for fish and make recreational activities unpleasant. This microscopic alga can be spread in a single drop of water.
Didymosphenia geminata is a diatom, which is a type of single-celled organism unique for their silica (SiO2) cell walls. The life history of diatoms includes both vegetative and sexual reproduction, though the sexual stage is not yet documented in this species. Although it is symmetric only along the apical axis, typical of gomphonemoid diatoms, it is a cymbelloid, which are typically symmetric along both primary axes. Cells contain a raphe, which allows them to move on surfaces, and an apical porefield, through which a mucopolysaccharide stalk is secreted.
The stalk can attach to rocks, plants, or other submerged surfaces. When the diatom cell divides, through vegetative reproduction, the stalk divides too, eventually forming a mass of branching stalks. The nuisance build-up is not the cell itself, but their massive production of extracellular stalks. Extracellular polymeric substances (EPS) that form the stalks are made primarily of polysaccharides and protein, forming complex, multi-layered structures that are resistant to degradation.
The native distribution of D. geminata is the cool temperate regions of the Northern Hemisphere, including the rivers of northern forests and alpine regions of Europe, Asia and parts of North America. Until its recent discovery in New Zealand, where it was introduced, it was never previously found in the Southern Hemisphere. The distribution of didymo in the last two decades appears to be gradually expanding outside its native range. Even within its native range, there have been reports of excessive growths in areas where it previously existed only in low concentrations.
Buryatia Widespread across large areas of Russia. Occurrence, ecology, water quality, and scanning electron micrography of D. geminata from Irokinda Mine Site, Buryatia, John G. Aronson, North American Diatom Symposium, Sept, 2011.
Alberta: Earliest anecdotal reports of D. geminata blooms in Alberta rivers occurred as early as the mid-1990s (e.g. the upper Bow River in Banff National Park). Reports of Didymo presence and bloom formation have been documented for most rivers in the South Saskatchewan River Basin in recent years (2005 to present).
British Columbia: D. geminata was first reported as a nuisance species in the late 1980s on Vancouver Island. Since that time, outbreaks of Didymo have been reported on the island and on the mainland.
New-Brunswick: D. geminata was first reported in 2007.
Arkansas: In late spring / early summer of 2005, didymo was found directly below Bull Shoals Dam on the White River. The Arkansas Department of Environmental Quality has found a 13-mile reach of the river to be affected.
Arizona. Found in Oak Creek just above the Pine Flat Campground in late August 2015
California: Rock snot has been around in Northern California for quite some time, and is commonly found on the North and South Fork of the Yuba River. It can also be found in reservoirs such as Lake Shasta, Bullard's Bar Reservoir, and Scotts Flat Lake.
Colorado: The range of Didymosphenia geminata was extended into Colorado by limnologist John G. Aronson, who collected it in 1976 from upper Fish Creek, near Steamboat Springs, Colorado.
Connecticut: In 2011 anglers reported blooms of didymo in the West Branch of the Farmington River to the Connecticut Department of Energy and Environmental Protection.
Idaho: According to the Idaho Department of Fish and Game, didymo has been identified along the South Fork of the Boise River for a number of years. Biologists cannot say for sure if it is native to the drainage, or has appeared in the last 10 to 15 years.
Kentucky: Didymo was found in the Cumberland River below Wolf Creek Dam in the Crocus Creek area 2008. The State of Kentucky has banned felt-soled waders in the river to prevent spread of the organism.
Maryland: In May 2008, didymo was found in the Gunpowder River in Baltimore County. In December 2009, it was found in the Savage River in western Maryland. In May 2012, its presence was confirmed in Big Hunting Creek in Frederick County.
New York: In August 2007, didymo was first discovered in New York State in a section of the Batten Kill, a Hudson River tributary, in Washington County. It has also been found in Esopus Creek in the Catskills. Black Creek Washington County
North Carolina: A slithery, mucous-like algae known as “rock snot” is the latest in a long line of invasive species haranguing Western North Carolina’s famous trout waters. The N.C. Wildlife Resources Commission is advising anglers to use extra caution when cleaning their equipment to prevent the spread of didymo (short for Didymosphenia geminate), a nuisance algae, which was recently found in the Tuckasegee River in Jackson County]].
Pennsylvania: Didymo has been confirmed in the Delaware River. In 2012, its presence was confirmed in the Youghiogheny River. In 2013, PA Department of Environmental Protection put out an alert that it has now been discovered in Pine Creek, Lycoming County.
South Dakota: Didymo has been present in Rapid Creek in South Dakota since at least 2005, and is blamed for a significant decline in the brown trout population there. It is also present to lesser extents in other nearby locations.
Vermont: In June 2007, didymo was discovered in the Connecticut River near Bloomfield, Vermont, its first recorded discovery in the northeastern United States. The sighting was reported by a fishing guide and confirmed by Dr. Sarah Spaulding, a didymo expert from Denver, Colorado.
West Virginia: In 2008, didymo was found in West Virginia in the Elk River in Webster County near Webster Springs and in Glady Fork and Gandy Creek, both in Randolph County. The alga was found in Seneca Creek in Pendleton County in 2009.
Chile: In 2010, the United States Geological Survey (USGS) and a Chilean laboratory, Centro de Investigacion en Ecosistemas de la Patagonia (CIEP), confirmed the identification of the diatom D. geminata (didymo) as forming extensive blooms in Chilean rivers in Chile's Los Lagos Region (X Región de Los Lagos) in the Andes west of Esquel, a town in the Chubut Province of Argentina, with reports from the Espolon River and the Futaleufú River for a total of more than 56 river kilometers affected.
D. geminata was discovered in New Zealand in 2004, the first time it was found in the southern hemisphere. To restrict its spread, the whole of New Zealand's South Island was declared a controlled area in December 2005. Extensive publicity was carried out to limit the spread, but it has subsequently been found in an increasing number of rivers there.
Preventing further spread
The following methods have been recommended to prevent the spread of didymo in New Zealand:
Check: Before leaving the river, remove all obvious clumps of algae and look for hidden clumps. Leave them at the site. If you find clumps later don't wash them down the drain, treat them with the approved methods below, dry them and soak them in bleach for at least 4 hours.
Clean: Soak and scrub all items for at least one minute in either hot (60 °C) water, a 2% solution of household bleach, antiseptic hand cleaner, or dishwashing detergent.
Dry: If cleaning is not practical (e.g. livestock, pets), after the item is completely dry wait an additional 48 hours before contact or use in any other waterway.
New Zealand and the U.S. states of Alaska, Maryland, South Dakota and Vermont have banned anglers from wearing felt-soled boots. Orvis, a leading U.S. manufacturer of fly-fishing equipment, has started selling more rubber-soled boots than felt-soled.
Theory on the Didymo Problem
New research says the green slime is not an invasive species wreaking havoc across Canada and around the world, as once believed. The study by Environment Canada and Dartmouth College in New Hampshire found that Didymosphenia geminata may already pervasively exist around the world, simply responding to changing environmental conditions. Dr. Max Bothwell at Environment Canada claims that phosphorus poor streams create blooms of the algae. The research paper, "Blooms of benthic diatoms in phosphorus‐poor streams" was first published in March 2017.
From Vancouver Island University News:
"I started questioning if introduction by anglers could be causing all of this and decided it couldn't be. I began thinking of the Heber River as the smoking gun," said Bothwell. "Blooms were occurring all over the world now, but why did this start happening on Vancouver Island over 10 years previously? What was so special about this place?"
The forestry reports they uncovered showed that in the 1980s the British Columbia government in Canada started one of the largest forest fertilization programs in the world. They used helicopters to drop more than 1 million kilograms of urea fertilizer on forests to increase tree production. The data showed some of the first drops occurred in the Heber River watershed.
Bothwell now had a solid event he could focus on. After running experiments and looking at water quality data from that time Bothwell focused in on phosphorus levels in the Heber and was shocked by what he found. Instead of phosphorus levels rising in the rivers due to the fertilizer drops, it actually dropped to next to nothing.
"When they started fertilizing the forests it stimulated not just tree growth but all soil microbial activity. The forest floor is a huge network of microorganisms and it was taking up the phosphorus that would usually run into the river," said Bothwell. "We could finally show that the aggressive growth of rock snot is caused by ultra-low phosphorus conditions, something that was very hard to accept. We all knew that adding more nutrients, especially phosphorus, to a river system always equals more algae and here I came face-to-face with the exact opposite of that. It was unbelievable."
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- Barringer, Felicity (August 15, 2010). "Fly Fishers Serving as Transports for Noxious Little Invaders". The New York Times. Retrieved August 17, 2010.
- Bothwell, Max L.; Taylor, Brad W. (2017). "Blooms of benthic diatoms in phosphorus‐poor streams". Blooms of Benthic Diatoms in Phosphorus‐poor Streams (2 March 2017). 15 (2): 110–111. doi:10.1002/fee.1466.
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- AlgaeBase - taxonomic and nomenclatural information
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- River Mystery Solved Scientists discover how “Didymo” algae bloom in pristine waters with few nutrients. Redorbit.com
- Species Profile- Didymo (Didymosphenia geminata ), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Didymo.