Didymo | National Invasive Species Information Center

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National Invasive Species Information Center

U.S. Department of Agriculture

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Rock snot (didymo) - Photo by T. Thorney

Scientific Name:

Didymosphenia geminata (Lyngb.) M. Schmidt (ITIS)

Synonym:

Gomphonema geminata (Lyngb.) C. Agardh (ITIS)

Common Name:

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; Spaulding and Elwell 2007)

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.

Images

Google Images - Didymo

Google.

Videos

YouTube - Didymo, Shedding Light on a Mysterious Algae

Google. YouTube; Montana Fish, Wildlife, and Parks.

Selected Resources

The section below contains highly relevant resources for this species, organized by source. Or, to display all related content view all resources for Didymo.

Partnership

Global Invasive Species Database - Didymosphenia geminata (algae)

IUCN. Species Survival Commission. Invasive Species Specialist Group.

Invasive Species Compendium - Didymosphenia geminata

CAB International.

NEANS Panel Online Guide - Didymo (a.k.a. rock snot)

Northeast Aquatic Nuisance Species Panel.

New York Invasive Species Information - Rock Snot, Didymo

New York Invasive Species Clearinghouse.

Federal Government

GLANSIS - Rock Snot

DOC. NOAA. Great Lakes Environmental Research Laboratory; DOI. USGS. Wetland and Aquatic Research Center.

Yosemite National Park - Invasive Species: Didymo a.k.a. "Rock Snot"

DOI. National Park Service.

See also: Environmental Factors - Invasive Species for more information

International Government

Biodiversity and Pest Control - Didymo

Otago Regional Council (New Zealand).

State and Local Government

Freshwater Aquatic Invasive Species Threatening Rhode Island: Didymo (Sep 2017) (PDF | 682 KB)

Rhode Island Department of Environmental Management. Office of Water Resources.

See also: Aquatic Invasive Plants for species of concern

AIS Action Plan: Didymo (Jun 2011) (PDF | 193 KB)

Pennsylvania Fish and Boat Commission.

See also: Aquatic Invasive Species for more action plans

Animals, Plants, Aquatic Life - Didymo (Rock Snot)

New York Department of Environmental Conservation.

Didymo (Invasive Freshwater Algae) in Virginia

Virginia Department of Wildlife Resources.

Didymo (Rock Snot) Fact Sheet

West Virginia Department of Natural Resources.

Invasive Plants in Pennsylvania: Didymo (PDF | 153 KB)

Pennsylvania Department of Conservation and Natural Resources.

See also: Invasive Plant Fact Sheets for plant species (trees, shrubs, vines, herbs and aquatic plants) that have impacted the state's natural lands

Invasive Species: Didymo (PDF | 341 KB)

Missouri Department of Conservation.

See also: Don't Spread Didymo for more information

Maryland's Invasive and Exotic Species - Didymo: Invasive Algae

Maryland Department of Natural Resources.

New Aquatic Nuisance Species Threatens Maine Streams and Rivers: Didymo or "Rock Snot"

Maine Department of Environmental Protection.

Academic

Didymo (or Rock Snot)

University of California - Riverside. Center for Invasive Species Research.

Factsheet: Didymo

Pennsylvania State University. Pennsylvania Sea Grant.

See also: Aquatic Invasive Species: Resources for additional species information

National Invasive Species Awareness Week: Didymo

Michigan State University Extension.

Citations

Bergey, E.A., J.T. Cooper, and C.R. Tackett. 2009. Occurrence of the invasive diatom Didymosphenia geminata in southeast Oklahoma. Publications of the Oklahoma Biological Survey, 2nd Series 9:13-15.
Integrated Taxonomic Information System. Didymosphenia geminata. [Accessed Sep 10, 2014].
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.
Spaulding, S.A. and L. Elwell. 2007. Increase in nuisance blooms and geographic expansion of the freshwater diatom Didymosphenia geminata (PDF | 1.08 MB) (Open-File Report 2007-1425) Reston, Va.: U.S. Geological Survey.