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| Didymosphenia geminata cell, 400x magnification; VT DEC |
Didymo stalk material on Connecticut River rock; VT DEC |
Didymo stalk material on Connecticut River bottom; NH DES |
Didymosphenia geminata, also known as didymo or rock snot , is a freshwater diatom (a type of algae) that has been producing nuisance blooms in rivers of the northeastern U.S. and Canada since 2006. Until 2006 didymo was unheard of in the northeastern U.S. Though originally native to far northern latitudes of Europe, Asia, and North America, it has undergone a recent large range expansion. Didymo is now found in many western U.S. and Canadian rivers, some tailwater rivers in the southern United States and, more recently, in some northeastern provinces and states, as well as other locations around the world (for a complete listing of known locations in the northeast, see below).
Individual didymo cells can t be seen without a microscope but they can produce a fibrous stalk that can develop into visible mats sometimes as much as several inches thick that carpet a stream bottom. Presence of these mats has been shown to alter the composition of aquatic insect communities reducing the relative abundance of mayflies, caddisflies, and stoneflies while increasing the relative abundance of midges and worms. These changes could, in turn, negatively impact fish communities. Although to date there is no conclusive evidence linking fish declines to didymo blooms, studies are ongoing. Since we don t know what the long-term impact of didymo nuisance blooms will be, all recreationists and professionals are strongly urged to incorporate spread prevention practices for didymo into their activities, to minimize further spread of this species to new waters.
For information:
- For NEANS panel spread prevention recommendations click here State and Province specific didymo information:
- Additional national and international didymo information
Didymo distribution in the Northeast as of August 2008:
Connecticut
- No didymo has been reported
Maine
- No didymo has been reported
Massachusetts
- No didymo has been reported
New Brunswick
Restigouche River and tributaries (Kedgwick, Patapedia, Upsalquitch, Matapedia), New Brunswick
- First documented early fall 2007
- Nuisance blooms 2007
Shikatehawk Stream (Upper St. John River drainage), New Brunswick
- First documented October 2007
- Nuisance blooms 2007
New Hampshire
Connecticut River
- First documented July 2007
- Nuisance blooms in 2007 and 2008
Mohawk River (a tributary of the Connecticut)
- First documented June 2008
- Nuisance bloom in 2008
New York
Batten Kill
- Anecdotally observed summer 2006; first documented July 2007
- Nuisance blooms 2006; nuisance level blooms were not observed in 2007 or 2008
Delaware River
- First documented fall 2007
- Nuisance blooms 2007 and 2008
Nova Scotia
- No didymo has been reported
Quebec
Matane river
- First documented 2006
- No known nuisance bloom (cells were detected in 2006 but nuisance level blooms were not observed)
Sainte-Anne river, Quebec
- First documented 2006
- No known nuisance bloom (cells were detected in 2006 but nuisance level blooms were not observed)
Bonaventure river, Quebec
- First documented 2007
- No known nuisance bloom (cells were detected in 2006 but nuisance level blooms were not observed)
Humqui river, Quebec
- First documented 2007
- Nuisance blooms 2007
Nouvelle river, Quebec
- First documented 2006
- Nuisance blooms 2007
Petite Cascapadia river, Quebec
- First documented 2006
- Nuisance blooms 2007
Cascapadia river, Quebec
- First documented 2006
- Nuisance blooms 2007
Rhode Island
- No didymo has been confirmed (but see also notable , below)
Vermont
White River, Vermont (Connecticut River drainage)
- First documented July 2007
- Nuisance blooms 2007, 2008
Batten Kill, Vermont section
- First documented July 2007
- No known nuisance blooms (cells were detected in 2007 but nuisance level blooms were not observed)
Mad River
- First documented July 2008
- Nuisance blooms 2008
Also notable:
- Uncomfirmed 1988 report of didymo at several locations in Rhode Island in Freshwater and marine plants of Rhode Island by Robert G. Sheath and Marilyn M. Harlin
- Didymo (recorded as Gomphonema geminatum ) documented in blue clay deposits near Philadelphia by Charles S. Boyer, 1916
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