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Today I want to talk to you about an
invasive aquatic species with the potential to cause enormous economic and
ecosystem damage to the Western states and about a program for early detection
and detection that can help counter the threat.
The species I’m talking about is the
zebra mussel, Dreissena polymorpha. I’m sure you’re all familiar with
zebra mussels, so I’m going to move quickly through information about its
basic biology, spread, and current distribution in North America. After that,
I’ll discuss some of the ecosystem and economic impacts, and then talk about
the Zebra Mussel Monitoring Program.
mussels are a freshwater bivalve, which means they have two shells. The alternating light and dark
bands or stripes on their shells give them the name zebra mussels, of course.
Their average shell length is
about ¾”, although they come in a range of sizes from much smaller up to about
zebra mussels unique is their ability to attach to hard surfaces. They do this by means of byssal
threads. The ends of these threads are sticky, which allows zebra mussels to attach to a variety of
surfaces – rock, wood, rubber,
plastic, metal – almost anything that’s not toxic.
One reason zebra mussels are so prolific is their reproductive
cycle. A mature female can produce up to 1 million eggs per year, although the
average is probably closer to 300,000. The eggs are fertilized outside the
body and spawning peaks at a water temperature of around 68 degrees
Fahrenheit. During spawning, the water may be so thick with microscopic
larvae that a coffee cup scoop of water contains more than 100 larvae.
Each of the
microscopic larvae, called a veliger, is about the same diameter as a human hair. (You can see the veligers at the left side
of the top photo.) Veligers live in the open water and move about with the water
Two to four weeks after hatching, the free-swimming veligers need
to settle. These juveniles have latched on to a beer can, but any solid
object will do, including other zebra mussels. Zebra mussels can colonize soft,
when hard objects deposited in or on the mud – such as pieces of native mussel
shells or grains of sand – serve as a substrate.
normally find zebra mussel adults growing in colonies in water about 1 to 30
meters deep. Their cousins, the invasive species known as the quagga mussel, are
very similar but are more often found in deeper and colder conditions.
So where do they come from? The zebra
mussel was originally described by the famous Russian scientist and explorer
Pyotr Simon Pallas from a population in a tributary of the Ural River in the
Caspian Sea Basin (Pallas 1771). Aided by the expansion of commercial boat
traffic through newly constructed canals, this species spread west from Russia
into most of Europe during the 1800s.
It’s believed that they were
transported to North America in the ballast water of a large cargo vessel,
which is used to keep the vessel in trim when it’s not fully loaded.
Zebra mussels were found for the first
time in North America in 1988 in Lake St. Clair, which is part of the Great
Lakes system. Lake St. Clair is the small, heart-shaped lake between Lakes
Huron and Erie. The large red dot to the left of Lake St. Clair is the city of
Detroit, and zebra mussels quickly spread away from there.
How did they
spread? The larvae can spread on water currents, of course, but most zebra
mussels probably dispersed by attaching to solid objects, particularly boat
hulls, motors, and anchors. Latching onto barges may be an effective way for
zebra mussels to spread through river systems. In addition, zebra mussels may
colonize aquatic plants, for example, if boaters fail to clean the plants off
their boats and trailers when they pull their boats out of the water.
mussels can survive a long time out of water, depending on the temperature
(they like it cool), the humidity (more humid is better), wind (less wind is
preferable), and sunlight (they like shade). On average, adults can survive
about 10 days out of water and juveniles about 3 days, but they’ve been known
to survive as long as 21 days out of water in cool, moist conditions.
Here’s the current distribution of zebra
mussels in North America. As you can see, they’ve spread throughout the Great
Lakes and into the St. Lawrence Seaway, and also through the Mississippi,
Ohio, Illinois, Hudson, Tennessee and Arkansas River systems. They’re
currently found in 21 states and 2 provinces of Canada.
Note the red dot
on the Missouri River, east of Nebraska and just north of the Platte River.
That’s the population closest to the West Coast at the present time. Several
years ago, a group of state, provincial, and federal agencies looked at the
map of zebra mussel distribution and decided they didn’t want zebra mussels or
any other invasive species to come any closer to the West. The group is called
because their goal is to keep invasive species out of the 100th
meridian jurisdictions. (The 100th
meridian runs right through the middle of
North and South Dakota, Nebraska, and on down through Texas.)
program includes a number of components, including monitoring, which I’ll talk
about later. But first, it’s important to note that the timing of the 100th
Meridian Initiative was important too,
especially when you realize that the western states are expecting a lot of
tourism beginning in 2004 – especially along the route that might be the worst
choice if you want to prevent the spread of zebra mussels and other invasive
Of course, the tourists will be coming to
celebrate the bicentennial of the Lewis & Clark expedition. The sojourn
out follows the route from St. Louis on the Missouri River on over the
Continental Divide and eventually to the Snake and Columbia Rivers. It’s
expected that many tourists will be trailering boats as they make the trek
from the zebra mussel-infested waters of the east to the uninfested waters of
the west. Of course, zebra mussels latch onto boats, trailers, and aquatic
plants, so this is an effective way to introduce zebra mussels into the west.
The 100th Meridian Initiative
definitely wants to prevent this from occurring.
Even before the Lewis & Clark
Bicentennial, boat traffic into the Northwest from points east of the 100th meridian was noteworthy. On just one Web site
of boats that needed to be shipped around the country between May 21 and June 21,
2001, we found 21 boats destined for Washington, Oregon, and British Columbia.
Five of those boats were coming from Michigan, where zebra mussels infest many
Obviously, reservoirs, lakes, rivers, and other water
bodies in the West, including those along the Missouri River basin, attract
many boaters. This pathway is of particular concern, because many states have
no inspection programs in place to determine if travelers are transporting
zebra mussels. Only astute observation by an inspector from Washington
intercepted a boat from the Great Lakes that entered the state with live zebra
mussels aboard several years ago.
Obviously states such as South Dakota,
North Dakota, and Nebraska, which are within a day’s drive of zebra-mussel
infested waters, are at much greater risk.
Predicting which lakes and rivers are at greatest risk from zebra
mussels is difficult. However, there
are some important factors that determine where, and in what
quantity, the mussels are and could be found.
temperature. Although zebra mussels can exist in water temperatures that range from as
cool as 32 degrees Fahrenheit to as warm as 86 degrees Fahrenheit, they
generally prefer temperatures in the range from 54 to 68 degrees.
They also require
more calcium than many mussel species in North America. Typically, calcium
levels must be greater than 20 mg/l for zebra mussels to occur in a water
They prefer that water pH be only slightly basic, but can also
occur in water with higher pH.
They also prefer a fairly high dissolved
oxygen, so this is a limiting factor in some water bodies. Some mixing in a water body
to bring in dissolved oxygen is good, but zebra mussels don’t do well in a rapid current.
And finally, zebra
mussels prefer to live at a depth less than 30 meters and usually less than
10 meters. On the other hand, their cousin the quagga mussel does well in deeper
waters and at colder temperatures.
Why should we be concerned about zebra mussels? Because zebra
mussels can cause severe impacts to the ecosystem and to the economy.
First, zebra mussels are filter feeders.
They filter suspended material out of the water column and transfer it to the
benthos or bottom of water bodies. This can result in a decrease in the amount
of chlorophyll, phytoplankton, and primary production in a water body.
mussels can also suppress zooplankton populations by filtering water. In areas
of eastern Europe, the biomass of phytoplankton and zooplannkton decreased
more than 10-fold following the introduction of zebra mussels (Karatayev et
In addition, the decline in zooplankton populations due to
zebra mussel filtration can also affect fish community structure. In
particular, reducing the amount of zooplankton available can affect the growth
of fish that are planktivorous at some point in their development (MacIsaac
The aquatic food web can be like a house of cards, with a
precarious balance from phytoplankton to zooplankton to planktivorous fish to
piscivorous fish. If zebra mussels wipe out the lower trophic levels, the
entire food web can collapse.
course, zebra mussel filtering can improve water clarity, making the water nicer to look at. But as I
said, filtering can also change plant and animal communities. Each adult zebra
mussel can filter about one liter of water per day – but based on zebra mussel densities in the western
basin of Lake Erie, experts
calculate that zebra mussels filter all of the water in the basin once every three days.
In some ways that can be good. For example, in
lakes Erie and St. Clair, rooted aquatic plants have become established in areas
where they have been absent for a long time. In other
areas, aquatic plants are more dense than normal, and have extended into
deeper waters because the decrease in turbidity allows increased light
penetration. But increased clarity also open the door for invasive aquatic
species, resulting in lakes that look like the one in this photo.
Zebra mussels have
contributed to the increase in Lake Erie’s water clarity, which began with
the initiation of the phosphorus abatement programs in the 1970s. According to
Dr. Ruth Holland Beeton, who conducted research near Stone Laboratory on
Lake Erie in the 1970s before phosporus abatement programs, water
clarity was approximately 3 feet, improved to 6 to 10 feet in the 1980s after a
decade of reduced phosphorus inputs, and improved again to 10 to 17 feet in
the early 1990s, after zebra mussels colonized the area.
The prodigious filtering of water by
zebra mussels may also increase human and wildlife exposure to organic
pollutants (such as PCBs and PAHs). Early studies have shown that zebra
mussels can rapidly accumulate organic pollutants within their tissues to
levels more than 300,000 times greater than concentrations in the environment.
They also deposit these pollutants in their pseudofeces.
These persistent contaminants can be passed up the food chain so that any fish
or waterfowl consuming zebra mussels may also accumulate these organic pollutants.
Likewise, human consumption of these same fish and waterfowl could result in
further risk of exposure. The implications for human health, however, remain
Zebra mussels also compete with native organisms, particularly
other mussels. They
readily encrust native North American mussels (family
Unionidae). In Lakes St. Clair and Erie, heavy fouling by zebra mussels has
severely reduced populations of native mussels. Some native mussel species are
more tolerant to fouling than others, but even for those resistant species,
zebra mussel encrustation leads to reduced energy reserves and vulnerability
to other environmental stressors, such as extreme water temperatures, lack of
food, or parasites and disease. As zebra mussels spread, biologists are
concerned that populations of native mussels will decline, and perhaps some of
the rarer species may be completely eliminated.
Zebra mussels do have predators. In the Great Lakes, diving
ducks, such as goldeneyes, bluebills, and scaup feed on zebra mussels. In fact,
zebra mussels are such a great resource that the population of these waterfowl
is increasing and they are changing their overwintering and migration patterns
to take advantage
of the readily available food. Unfortunately these birds can’t consume enough
zebra mussels to control their populations.
Some fish species also prey on zebra mussels. Examples include
the freshwater drum, a fish that’s frequently called sheepshead, plus the common
carp, yellow perch, and round goby, another invasive species that’s made its
way into the Great Lakes. Again, these fish can’t consume enough zebra mussels
to keep their
populations in check.
mussels even cause ecosystem impacts out of the water. When they’re washed up onshore and die,
their decaying flesh gives off an unpleasant odor.
Also, their sharp shells make
swimming and wading and just walking on the beach extremely uncomfortable.
mussels can also impact boaters and shore land property owners. They can attach to boat hulls, clog boat engine cooling systems,
and clog water intakes. Scraping off the zebra mussels from an
encrusted hull can damage the boat’s
paint or gel coat. By growing in an
engine cooling system, they can block
water flow, which can cause the engine to overheat.
Shoreline property owners who
draw water from an infested lake or river can also find that their pumps and hoses are clogged, making
them inoperative. Of course,
the cost for these repairs are borne by only a few people, but everyone pays when zebra mussels impact
large utility systems.
In the West, zebra mussels pose a threat to
farm and orchard irrigation systems by choking off the flow in canals. From
the irrigation pump, the mussels could spread to the irrigation system and
totally block off the pipe, even those as large as 4 inches in diameter.
mussels affect industries and cities that draw water from the Great Lakes. Although utilities can
control zebra mussels using several different techniques, doing so has a high price tag. The cost is
passed along to customers
and taxpayers, of course.
example, from 1989 to 1994, zebra mussel control costs for industries and municipalities around the Great
Lakes were an estimated $120 million. An individual, medium-size city can spend $360,000 dollars a
year, a smaller city $20,000,
and a nuclear power plant up to $2 million annually.
Dense growths of zebra mussels on
breakwalls, locks and dams, and control structures are also of concern. Once
they colonize the interiors of turbines, pumps, and associated equipment,
removing them can be a costly proposition. They are also known to increase the
rate of corrosion of iron and steel structures at the point of attachment
mussels can also attach to fish ladders, fish diversion screens, and other pipes
and conduits that sensitive fish species use to make their way around dams.
Their shells are sharp and could injure passing fish; they could build up and
disrupt water flow; and ultimately, they could threaten other species, including
centuries, Europeans have not found a satisfactory control method for zebra
mussels. In the Great Lakes, no
technique has been developed that is both feasible for widespread use and not
harmful to other aquatic species.
Lake- or river-wide control of zebra mussels is simply not possible at this
A number of methods have been
tried, however. Proactive treatments include the following:
Coatings – The Corps of Engineers
has evaluated a variety of coatings, include some containing copper or zinc products, which are toxic to zebra mussels;
silicone-based systems that provide a low-tension, nonadherent surface; and thermal sprayed metallic coatings.
Chemical treatment involves use of oxidizing chemicals, nonoxidizing chemicals
and molluscides. When used,
chlorination involves injecting chlorine through a facility and then
dechlorination before the water is returned to the waterbody. The EPA requires that the discharge be
analyzed and monitored to demonstrate that the system works properly and meets EPA limits.
Temperatures above 95-100°F for several hours are lethal to zebra mussels, so
it’s possible to prevent zebra
mussels from colonizing structures by injecting steam or hot water and
circulating them through a facility periodically.
Filtration – In line filters with extremely small
mesh sizes can be used to filter the troublesome veligers, but backwashing can be a problem at high flow rates.
Reactive treatments include a few
Mechanical and high-pressure
water – Mechanical cutting devices and high-pressure water treatments
manual labor and hand tools. These can be used to dislodge zebra mussels from
large surface areas, such as those
found in power plants.
CO2 pellet blasting – Blasting
can also be an effective mechanical means of removing zebra mussels.
Freezing/dessication – Freezing
during the winter or desiccation at high summer temperatures can be effective
in killing a large portion of the
zebra mussel population. Where feasible, the population can be exposed by
levels, since the mussels are usually restricted to shallow areas above the
Radiation -- UV light (wavelengths between 40° and
4,000°) is a prospective zebra mussel control method. Researchers found that not only are zebra mussel
veligers sensitive to UV-B radiation (2800° - 3200°), but also adult zebra mussels were sensitive, provided that
the radiation was applied constantly. Veliger mortality was 42-percent after 1 hr, 85-percent after 2 hr, and
100-percent after 4 hr exposure to UV-B radiation.
So how do we combat the challenge of
zebra mussels and other invasive species? In the conclusion of their 2001
Management Plan, the National Invasive Species Council had this to say:
“Ultimately the greatest asset in meeting the invasive species challenge is an
informed and involved public.” In other words, the public needs to know about
invasive species and how they can help prevent their introduction and spread.
Meridian Initiative includes a number of
elements to inform people about invasive species and get them engaged in
activities to stop their introduction and spread. The Zap the Zebra brochure
explains the steps that boaters can take to stop the spread of zebra mussels
and other invasive species, including plants.
Voluntary boat inspections
and boater surveys will be conducted on major highways entering the 100th
meridian jurisdictions and at key lakes in
the west. Inspections will target boats, trailers, and potentially
contaminated equipment. Boaters will also be asked to participate in a survey
to find out their origin and destination. They’ll also be given a copy of the
Zap the Zebra brochure.
Education activities include presentations that
tell the public about the biology, impact and pathways for spreading zebra
mussels and what they can do to prevent it. Boat launch signs and
identification cards also tell the public how to identify zebra mussels, clean
boats and trailers to stop their spread, and contact the appropriate
authorities if they believe a water body contains zebra mussels.
Information Systems are the low-power radio stations that provide information
in national parks and other places of interest. Those along the Lewis &
Clark Trail will provide information about zebra mussels. Web sites also offer
relevant information on zebra mussels and how to stop their spread.
monitoring is a key activity for education and early detection of invasive
The Zebra Mussel Volunteer Monitoring
program uses sampling substrates for early detection of zebra mussels. The
substrates are simply a piece of PVC pipe with holes drilled in it, mesh
inside attached with a cable tie, two washers to weigh down the pipe in the
water, and a rope to attach to a dock.
We also provide monitoring
protocols that tell the volunteer how best to attach the substrate to their
dock, how to check the substrate, and what to do if they find a
suspicious-looking critter. We ask volunteers to check the substrate once each
month. In general, monitoring takes about 20 minutes a month, depending on
The substrate is actually one of the key elements of our
education program. We ask volunteers to talk to others about their monitoring
activities and the need to protect water bodies from invasive species like
To provide us with their monitoring
results, volunteers either send in a response card each month or answer
similar questions in an e-mail message. They fill in information including
their name, location, and date, and then answer questions such as Do you still
have the trap? Did you see anything in the mesh? Do you need a new mesh? Do
you need educational materials?
Probably the most important question is
How many people have you talked to this month about zebra mussels? Remember,
we consider this an educational activity first and foremost, so we want our
volunteers to talk to their family, friends, neighbors, and colleagues about
sampling and invasive species.
Once every three months, we try to send out
additional information that volunteers might find useful, including an update
on zebra mussel distribution, any new sightings, and descriptions of other
invasive species. Here’s the newsletter we sent out in January 2003.
Right now, we have 182 substrates
located in 8 western states. In many places, individual volunteers monitor for
zebra mussels, but in some places a coordinator either handles the monitoring
or collects results from other individuals and reports to the Zebra Mussel
Volunteer Monitoring Coordinator. For example, Lynn Schlueter in North Dakota
is in charge of nine substrates, including six at Lake Sakakawea. Another
resource manager, Don Archer, coordinates all of the sampling in Utah.
love to enlist more volunteer monitors, of course, especially in the Missouri
River Valley. This area may be at particular risk for zebra mussel infestation,
because many sites are within a day’s drive of infested waters.
The Zebra Mussel Volunteer Monitoring
program was in effect for many months and no one reported seeing an invasive
species. Then in July 2002, a volunteer at Garrison Lake on the southeast
Oregon Coast noted an unusual snail in her sampling substrate. This picture
shows the substrate hanging off the dock in Garrison Lake – and if you look
closely, you’ll see black clumps in the water.
Those black clumps are New
Zealand mud snails. The snails were first found in the Snake River in the late
1980s and now occur in densities as high as 300,000 to 500,000 per square
meter in some rivers in the West, including the Madison and Yellowstone.
Biologists are concerned that they could negatively impact trout and salmon
populations by outcompeting native snails and insects.
Here’s Alice Pfand,
the volunteer who found the New Zealand mud snails. In January, the Oregon
Invasive Species Council honored Alice with their Eagle Eye Award for
detecting the mud snails. Alice received some publicity for the award, which
was great: The press recognized her contribution and also helped spread the
invasive species message.
So what can you do to prevent the
introduction and spread of zebra mussels and other invasive species?
of course, don’t spread them yourself! If you have a boat, make sure you inspect
it and remove all plants and animals every time you pull it out of the water.
Drain all water from your boat and equipment, including bilges, live wells,
bait buckets, and coolers. Power washing your boat or washing it with water
more than 110 degrees Fahrenheit and then letting it dry is another way to
make sure no critters survive.
Even if you just work around water, you
need to check your clothing, boots, and gear every time you leave a water
body. Small invasive species like New Zealand mud snails can easily get inside
your wading boots and hide there until you move to another water body.
fall 2002, zebra mussels were found for the first time in the state of Virginia.
An astute observer identified them in a quarry that’s popular with divers.
It’s very likely that they were transported there by an individual who had
been diving in infested waters – and who had no idea that zebra mussels had
latched onto his or her equipment. That’s why you have to be vigilant!
you see a species that looks suspicious, contact the invasive species
toll-free hotline at 800-437-2744. This
number is good anywhere in the west.
you can become a volunteer monitor for invasive species. Monitoring water bodies for zebra mussels
provides an enormous service to the
western United States.
If you’re interested in becoming a
volunteer monitor, you can contact the coordinator for the Zebra Mussel
Volunteer Monitoring Program in Portland, Oregon, at 503-725-9075. You can
also send an e-mail to email@example.com. And finally, I brought with me
the forms you need to fill out to become a volunteer monitor. You can send
these directly to the monitoring coordinator and receive a substrate and
protocols so that you can start monitoring right away.
preventing the spread of invasive species like zebra mussels can be done! With
your help, we can keep zebra mussels out of the West.
Thanks for your attention. I’d be happy to answer questions now …