Didymosphenia geminata

Didymosphenia geminata
Didymo found beside the Mararoa River in New Zealand.
Scientific classification
Domain:	Eukaryota
Kingdom:	Chromalveolata
Phylum:	Heterokontophyta
Class:	Bacillariophyceae
Order:	Cymbellales
Family:	Gomphonemataceae
Genus:	Didymosphenia
Species:	D. geminata
Binomial name
Didymosphenia geminata (Lyngbye) M. Schmidt, 1899
Synonyms
Echinella geminata Lyngbye, 1819 Gomphonema geminatum (Lyngbye) C. Agardh, 1824

Didymosphenia geminata, commonly known as didymo or rock snot, is a species of diatom that grows in warm and shallow water. If it overgrows, it can form large mats on the bottom of lakes, rivers and streams. 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. It is considered a nuisance organism or invasive species. The microscopic algae can be spread in a single drop of water.

Cell biology

Scanning electron micrograph of the silica cell wall of D. geminata. Scale bar is 50 μm. Image by Sarah Spaulding, USGS.

Didymosphenia geminata is a diatom, which is a type of single-celled algae 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.

Native range

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.

Regions

South America

Chile: The United States Geological Survey [USGS] confirmed the identification of the diatom Didymosphenia geminata ("Didymo") as forming extensive blooms in Chilean rivers near Esquel, in the Chubut Province of Argentina. The bloom was reported on Espolon River and Futaleufú River, for a total of more than 56 river kilometers affected. These two rivers are located in the Los Lagos Region, Region X of Chile, Chiloe District. The result was confirmed by a Chilean laboratory, Centro de Investigacion en Ecosistemas de la Patagonia (CIEP) on 28 May, 2010.

New Zealand

Signs posted by Biosecurity NZ to warn of didymo threat in Waiau River.

Main article: Didymo in New Zealand

In 2004 D. geminata was discovered in New Zealand, the first time it was found in the southern hemisphere. To restrict its spread, the whole of the South Island of New Zealand was declared a controlled area in December 2005. Extensive publicity was carried out to limit the spread but it was found in an increasing number of rivers.

North America

Distribution map - Confirmed presence of Didymosphenia geminata in the United States and Canada. Source: EPA 2007

Sign on New York's Esopus Creek advising anglers about didymo

British Columbia: Didymosphenia 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.

Alberta: Earliest anecdotal reports of Didymosphenia 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 current).

South Dakota: It 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. It is also present to lesser extents in other nearby locations.

Tennessee: Didymo was found in the tailwaters of the Norris, Cherokee, Wilbur and South Holston hydroelectric dams in 2005. It is the first U.S. finding east of the Mississippi River.

Virginia: Didymo was identified in western Virginia in the summer of 2006 in the Smith River, the Jackson River, and the Pound River.

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.

New Hampshire: Also during the summer of 2007, didymo was discovered for the first time in New Hampshire in the Connecticut River near Pittsburg.

New York: In August 2007, didymo was first discovered in New York State in a section of the Batten Kill in Washington County. It has also been found in Esopus Creek in the Catskills.

Maryland: In May 2008, didymo was found in the Gunpowder River in Baltimore County.

Preventing the 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 put them in a rubbish bin.

Clean: Soak and scrub all items for at least one minute in either hot (60°C) water, a 2% solution of household bleach or a 5% solution of salt, 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 and Vermont have banned anglers from wearing felt-soled boots. Maryland is considering doing so as well. Orvis, a leading U.S. manufacturer of fly-fishing equipment, has started selling more rubber-soled boots than felt-soled.

External links

• AlgaeBase - taxonomic and nomenclatural information
• "Didymosphenia geminata". Integrated Taxonomic Information System. Retrieved 17 July 2007.
• CISR: Rock Snot - information on Didymosphenia geminata from the Center for Invasive Species Research
• Species Profile- Didymo (Didymosphenia geminata ), National Invasive Species Information Center, United States National Agricultural Library. Lists general information and resources for Didymo.