Don't Spread Didymo !
Please help to do your part to stop the
spreading of this highly invasive algae that has
already gained a foothold in the Connecticut
River and highly suspect in the White River...
Didymo - aka "Rock Snot" |
Didymo Frequently Asked Questions
Q: What is Didymo?
Didymosphenia geminata also known as
“Rock Snot” or more commonly “Didymo” is a
single-celled, freshwater alga or diatom. While
the individual cells are invisible to the naked
eye, Didymo can form large colonies or mats that
attach via a stalk to rocks and plants
smothering the bottoms of streams and rivers
with a thick yellow/brown layer of growth. The
massive blooms can form distinctive flowing
‘rats tails’ that turn white at their ends and
look similar to tissue paper. Since the 1980s,
this once rare species has been expanding its
geographic range and forming excessive growths
covering miles of stream reaches
Q: Why is Didymo a problem?
These massive nuisance growths may impact
freshwater fish, aquatic plants, and important
aquatic insects. Didymo blooms can reduce the
amount and availability of suitable habitats
(Biosecurity NZ, 2005). When large mats are
present impacts can include: reduced size and
density of some larval aquatic insects
(caddisflies, stoneflies, and mayflies),
increased populations of invertebrates typically
associated with degraded stream habitat (midge
larvae, oligochaete worms), a reduction of clean
substrate for fish nesting and egg laying, and a
decline in large, adult fish (EPA, 2006)
Economic impacts include fouling of water
intakes and, in heavily infested areas, Didymo
may be linked to a decline in freshwater angling
and related tourism. Impacts to aesthetics are
common, with reports of unsightly masses that
appear like strands of toilet paper leading to
concerns about sanitation and sewer
malfunctions. The heavy, slippery brownish mats
degrade swimming areas and also foul fishing
gear.
Direct human impacts may be limited to swimmers
complaining of eye irritation after swimming in
affected areas (Kilroy, 2004).
Q: Is Didymo an invasive species?
Although considered to be native to the northern
boreal regions of the Northern Hemisphere, its
biological status in the United States remains
uncertain (ISSG, 2005). The recent range
expansion and appearance of excessive Didymo
growths in North America (defined by the EPA as
being those that cover more than 1 mile of
stream reach and persist for more than a few
weeks) suggest a precautionary management
approach is advisable. In order to increase
awareness of the problems posed by Didymo and to
reduce the risk of an unwanted introduction the
Oregon Invasive Species Council added Didymo to
the state’s 2006 100 Least Wanted Species list.
Scientists do not know what has changed to allow
Didymo to take on the characteristics of an
invasive species. It has been postulated that
the emerging invasive populations are the result
of a new genetic variant or strain of Didymo
that has broader environmental tolerances than
the original. It has also been suggested that
increased exposure to ultraviolet (UV) radiation
may favor Didymo growth by either reducing the
grazer population or limiting populations of
other algal species that might outcompete or
repress Didymo growth (Kilroy, 2004).
Q: How does Didymo spread?
Human-assisted movement of Didymo is the most
likely culprit in many introductions, including
long-distance dispersal such as the recent
discovery of Didymo in New Zealand. Clumps of
Didymo as well as single microscopic cells can
be moved around by boaters, anglers, hunters and
other aquatic recreationists. Didymo, like other
aquatic invasders of concern such as the New
Zealand mudsnail and whirling disease, can be
transported on wet felted soles and boots, damp
wading gear, and in any standing water
associated with boats or other types of gear.
It is possible that animals could spread Didymo
locally e.g., on the damp feet or feathers/fur
of birds or other organisms. Short-distance wind
aided dispersal has also been postulated (Kilroy
2004).
Q: What habitats are at risk?
Didymosphenia geminata tends to form excessive
mats in (EPA 2006):
* Low, stable flow
* Water 3 inches to 6 feet deep
* Moderate to high current
* Below outlets of lakes and reservoirs
* Sunny, open streams
Q: Can Didymo be eradicated?
No, that’s why it is so important to prevent the
spread of Didymo through clean boating, fishing
and other aquatic recreation practices.
Eradicating any microscopic organism from a
natural environment is difficult, especially in
an aquatic environment. To date there are no
known systematic attempts to eradicate invasive
blooms of Didymo.
Q: How can I tell if an algal growth is actually
Didymo?
Mats of Didymo are much more likely to be found
in a stream or river rather than a reservoir or
lake and should not be confused with blue/green
algal blooms. Didymo has a distinctive
appearance but tufts and mats can be thick
white, light gray, pale yellow-brown, or beige
(not green) masses. An excessive infestation may
cover over 90 percent of the river bottom in
many reaches and these masses may form ratty or
fringed tails that turn white and closely
resemble streaming toilet paper (EPA 2006).
Other times, these mats may resemble a
brownish/yellow shag carpet. Although Didymo
looks slimy, it’s actually spongy and sort of
scratchy rather like wet cotton wool (Kilroy
2004).
Q: Can I help slow the spread of Didymo?
You can help slow or even prevent the spread of
Didymo by taking these precautions:
Be aware of posted notices warning of aquatic
invasive species. These signs should give you
specific guidelines on how best to clean or
decontaminate all gear that comes into contact
with the infested waters.
Before leaving any river, check your shoes,
waders, life vest, boat hull, anchor, trailer.
tires, and other equipment for clumps of algae,
mud and plant fragments
Clean your gear thoroughly taking care to scrub
creases and compartments and empty any standing
water at the ramp or down a treated sewer
system. Equipment can be treated with a 5 min
soak in a 50% solution of Formula 409
Disinfectant or a 10 min soak in 6% solution of
Sparquat 256. Equipment can also be treated by
drying completely for at least two days.
Dedicated equipment is recommended for people
commonly using infested sites. Alternate
equipment should then be used when visiting
uninfested areas.
Under no circumstances should live fish, plants,
or other items be moved between waterways.
Q: If Didymo can be spread by birds and animals,
will it really make a difference if I clean my
gear?
Yes it will. Not only can you help slow the
spread of Didymo to locations where animal
assisted dispersal could be unlikely but also
clean gear habits can prevent the spread of
other invasive species of concern such as mud
snails, aquatic weeds, zebra mussels and
whirling disease, as well as prevent the
introduction of some invaders we might not yet
be aware of.
Didymo mat |
Cleaning Methods for Freshwater Activities
If you are moving items between waterways,
you must Check, Clean, Dry....
CHECK: Before you leave a river or lake,
check items and leave debris at site. If you
find any later, treat and put in rubbish.
Do not wash down drains.
CLEAN: There are several ways to kill
didymo. Choose the most practical treatment for
your situation which will not adversely affect
your gear.
Non-absorbent items...
Detergent:
soak or spray all surfaces for at least one
minute in 5% dishwashing detergent or nappy
cleaner (two large cups or 500 mls with water
added to make 10 litres); OR
Bleach:
soak or spray all surfaces for at least one
minute in 2% household bleach (one small cup or
200 mls with water added to make 10 litres); OR
Hot water:
soak for at least one minute in very hot water
kept above 60 °C (hotter than most tap water) or
for at least 20 minutes in hot water kept above
45 °C (uncomfortable to touch).
*Absorbent items require longer soaking times to
allow thorough saturation.
For example, felt-soled waders require:
Hot water:
soak for at least 40 minutes in hot water kept
above 45 °C; OR
Hot water plus detergent:
soak for 30 minutes in hot water kept above 45
°C containing 5% dishwashing detergent or nappy
cleaner; OR
*Freezing any item until solid will also kill
didymo.
DRY: Drying will kill didymo, but
slightly moist didymo can survive for months. To
ensure didymo cells are dead by drying, the item
must be completely dry to the touch, inside and
out, then left dry for at least another 48 hours
before use.
*If cleaning or drying is not practical,
restrict equipment to a single waterway.
*NOTE: The thicker and denser the absorbent
material, the better it will be at holding
moisture (and live cells), the slower it will be
to dry out and the more difficult it will be to
soak completely with cleaning solutions.
When cleaning gear, we recommend that you:
- Soak absorbent items for longer than specified
to ensure thorough saturation of the material
with the cleaning agent
- Follow manufacturer’s safety instructions when
using cleaning products
- Dispose of cleaning waste well away from
waterways
Quick Links...
Distribution map - Confirmed presence of D.
geminata in the United States and Canada
Biosecurity New Zealand
A rough field guide for identification of D.
geminata
Didymo called dire threat - Rutland Herald
7/11/07
Vermont Agency of Natural Resources - Press
Release 7/6/07
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