Didymo

Scientific name: Didymosphenia geminata (Lyngb.) M. Schmidt

Synonym: Gomphonema geminata (Lyngb.) C. Agardh

Common names: Didymo, Rock snot

Native To: Northern Europe and northern North America (Spaulding and Elwell 2007)

Date of U.S. Introduction: Was present in Canada in the late 1800s, but did not begin to cause problems until the early 1990s. It was first discovered east of the Mississippi River in 2005 in Tennessee. (Bergey et al. 2009; Schroeder 2005)

Images: Google and Biosecurity New Zealand

Videos: Introduction to Didymosphenia geminata (Didymo)
(or click Play button below)

Means of Introduction: Exact pathway unknown, but it spreads easily through contaminated fishing gear, particularly felt-soled waders (Kilroy and Unwin 2011)

Impact: Alters stream ecology by forming dense algal blooms that can cover up to 100 percent of stream bottoms (Spaulding and Elwell 2007)

Current U.S. Distribution: Scattered populations exist throughout the United States, including New England, the Mid-Atlantic Region, and the Western U.S.

• Didymo Map - North America (Jul 21, 2008; PDF | 240 KB)
• Didymo Map - New Hampshire and Vermont (PDF | 1.8 MB)

Management Plans: Aquatic Species

Selected Internet Resources:

• Federal Government
• State Government
• University/Academic
• International
• Organizations

Federal Government

Didymosphenia geminata
Integrated Taxonomic Information System.
Taxonomy

Didymosphenia geminata Article Citation Search - AGRICOLA Database
USDA. National Agricultural Library.
Research

Didymosphenia geminata: A nuisance freshwater alga
Environmental Protection Agency.
Photographs; Impacts; Controls

Didymosphenia geminata, "Didymo" or "Rock Snot"
DOI. FWS. Connecticut River Coordinator's Office.
Photographs; Introduction History; Habitat; Distribution

Increase in nuisance blooms and geographic expansion of the freshwater diatom Didymosphenia geminata (PDF | 1.1 MB)
DOI. United States Geological Survey.
Identification/Description; Photographs; Introduction History; Impacts; Life Cycle; Habitat; Distribution; Dispersion; Controls

Invasive algae show up in some TVA tailwaters (Aug 2005)
Tennessee Valley Authority.
Identification/Description; Photographs; Impacts; Habitat; Distribution; Controls

State Government

New Aquatic Nuisance Species Threatens Maine streams and Rivers: Didymo or "Rock Snot"
Maine Department of Environmental Protection. Bureau of Land and Water Quality.
Photographs; Distribution; Controls

Didymo (a.k.a. rock snot) found in Vermont and New Hampshire
New Hampshire Department of Environmental Services.
Identification/Description; Photographs; Impacts; Habitat; Distribution; Dispersion; Controls

Didymo Alert
New York Department of Environmental Conservation.
Identification/Description; Photographs; Impacts; Habitat; Distribution; Dispersion

Do you know about Didymo?
Pennsylvania Fish and Boat Commission.
Identification/Description; Photographs; Distribution; Dispersion; Controls

Nuisance Algae: Didymosphenia geminata ("Didymo")
South Dakota Department of Environment & Natural Resources.
Identification/Description; Photographs; Impacts

Didymo or Rock Snot (Didymosphenia geminata) in Vermont and the Northeast
Vermont Agency of Natural Resources. Department of Environmental Conservation. Water Quality Division.
Identification/Description; Photographs; Introduction History; Impacts; Distribution; Controls

Didymo (Invasive Freshwater Algae) in Virginia
Virginia Department of Game and Inland Fisheries.
Introduction History; Impacts; Controls

Didymo (Rock Snot) Fact Sheet
West Virginia Department of Natural Resources.
Identification/Description; Photographs; Distribution; Controls

University/Academic

Didymo (or Rock Snot)
University of California, Riverside. Center for Invasive Species Research.
Photographs; Impacts; Distribution; Dispersion; Controls

How Didymo Became Rock Snot (Dec 2009)
University of Minnesota. Minnesota Sea Grant.
Photographs; Introduction History; Habitat; Dispersion

Didymo: Didymosphenia geminata (PDF | 267 KB)
Pennsylvania Sea Grant.
Identification/Description; Photographs; Introduction History; Impacts; Habitat; Distribution; Dispersion; Controls

International

Are you putting Australia's future on the line? (PDF | 832 KB)
Australian Department of Agriculture, Fisheries and Forestry. Australian Quarantine and Inspection Service.
Impacts; Distribution; Controls

Didymosphenia geminata in British Columbia Streams
British Columbia Ministry of Environment (Canada).
Identification/Description; Photographs; Impacts; Habitat

Didymosphenia geminata - Invasive Species Compendium
Centre for Agricultural Bioscience International (CABI).
Taxonomy; Identification/Description; Photographs; Impacts; Life Cycle; Habitat; Distribution; Controls

Didymo
Environment Bay of Plenty Regional Council (New Zealand).
Identification/Description; Photographs; Impacts; Controls

Didymo
New Zealand Ministry of Agriculture and Forestry. Biosecurity New Zealand.
Identification/Description; Photographs; Introduction History; Impacts; Distribution; Controls; Legal Aspects

Didymo
Otago Regional Council (New Zealand).
Identification/Description; Photographs; Introduction History; Controls

What Is Didymo and How Can We Prevent It From Spreading In Our Rivers? (Mar 2007; PDF | 332 KB)
Quebec Ministry of Sustainable Development, Environment, and Parks; Quebec Ministry of Natural Resources and Wildlife (Canada).
Identification/Description; Photographs; Impacts; Distribution; Dispersion; Controls

Didymosphenia geminata (algae) - ISSG Global Invasive Species Database
World Conservation Union. Invasive Species Specialist Group.
Taxonomy; Identification/Description; Photographs; Impacts; Life Cycle; Habitat; Distribution; Dispersion; Controls

Organizations

Don't Let Adirondack Rivers Get Slimed! (PDF | 90 KB)
Au Sable River Association (New York).
Identification/Description; Photographs; Impacts; Dispersion; Controls

Didymosphenia geminata
Federation of Fly Fishers.
Identification/Description; Photographs; Impacts; Habitat

Didymo - Lake George Fact Sheet No. 23 (Jan 2010; PDF | 151 KB)
Fund for Lake George (New York).
Photographs; Impacts; Habitat; Distribution; Controls

Didymo (Didymosphenia geminata)
Maryland Invasive Species Council.
Identification/Description; Photographs; Introduction History; Distribution; Controls

Citations

Bergey, E.A., J.T. Cooper, and C.R. Tackett. 2009. Occurrence of the invasive diatom Didymosphenia geminata in southeast Oklahoma (PDF | 79 KB) Publications of the Oklahoma Biological Survey, 2nd Series 9:13-15.

Kilroy, C. and M. Unwin. 2011. The arrival and spread of the bloom-forming, freshwater diatom, Didymosphenia geminata, in New Zealand. Aquatic Invasions 6(3):249-262.

Schroeder, O. 2005. Invasive algae 'Didymo' found in Tennessee River. Tennessee Wildlife Resources Agency.

Spaulding, S.A. and L. Elwell. 2007. Increase in nuisance blooms and geographic expansion of the freshwater diatom Didymosphenia geminata (PDF | 1.08 MB) U.S. Geological Survey. Open-File Report 2007–1425.