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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.
Zebra 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 2”. What makes 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 currents. 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, muddy bottoms when hard objects deposited in or on the mud – such as pieces of native mussel shells or grains of sand – serve as a substrate. Finally, you 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. Zebra 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 the 100th Meridian Initiative, 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.) Their 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 species.
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 water bodies. 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. First is 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 body. 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. Zebra 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 al. 1997). 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 1996). 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.
Of 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 unclear.
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.
Zebra 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.
Zebra 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.
Zebra 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. For 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 Zebra 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 endangered salmon.
After two 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 time.
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. Chemicals – 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. Thermal – 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 other possibilities:
Mechanical and high-pressure water – Mechanical cutting devices and high-pressure water treatments typically involve 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 lowering water levels, since the mussels are usually restricted to shallow areas above the thermocline. 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.
The 100th 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. Traveler 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. Finally, monitoring is a key activity for education and early detection of invasive species.
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 travel time. 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 zebra mussels.
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. We’d 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? First, 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. In 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! If 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. Finally, 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 invasivespecies@pdx.edu. 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. Remember, 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 …