Aquatic invasive species (AIS)—which include plants, animals, and viruses—are a serious challenge for our lakes. Lake associations, lake districts, and individual waterfront property owners are rightfully concerned about the potential impact that invasive species can have on lake ecosystems and recreation. Many groups are investing private (and state) dollars into treating waters for invasives like Eurasian water milfoil, curly leaf pondweed, and carp. Many lake groups are participating in public education campaigns (like Clean Boats, Clean Waters) to encourage boaters to take simple to prevent the spread of AIS. Others are organizing volunteers to conduct AIS monitoring.

Introduction non-native species are not a new phenomenon. Some non-native species—like Eurasian water milfoil and carp—become invasive in new environments. But the introduction of AIS into a lake does not necessarily mean the destruction of the lake. Wisconsin has many invasive species at different stages of colonization. And more invasive species are on the horizon. Our scientific understanding of strategies for prevention, containment, and management is still evolving. A strategic combination over time of volunteer effort, continuing scientific research, legislation, funding, administrative rules, county ordinances, prevention programs, and educational efforts are all necessary to make progress on AIS.

More people, more places, more vectors for invaders

Not all non-native species become invasive

Disturbance and possible invasions

Prevention, containment, management

Using lake classification for AIS work

Introduction of non-native species has a long history 

More People, More Places, More Vectors For Invaders

As human populations have become more mobile, and movement has become more global, so have the species we move around with us. Unwanted hitchhikers can be speedily transported on planes, boats, and cars across town or across the ocean. Transfer of water between water bodies can introduce pieces of invasive plants, organisms, and pathogens into unaffected waters. Boaters can take simple steps to prevent transportation of AIS from lake to lake by:

• Inspecting and remove aquatic plants, animals, and mud from boat, trailer, and equipment before leaving the landing.
• Draining all water from boat, motor, live wells, bilge, bait buckets and other containers before leaving the landing.
• Icing your catch; don’t leave landing with any live fish, bait, or fish eggs.
• Disposing of unused bait in trash, not in the water or on land.
• Rinsing boat and equipment with hot or high pressure water OR Dry boat for at least five days.

When ocean going ships—called “salties”—flush their ballast water tanks, they can deposit exotic stowaways directly into the Great Lakes. Some of these hitchhikers—zebra mussels, sea lampreys, viral hemorrhagic septicemia, and the New Zealand mud snail—have thrived in their new habitats, becoming invasive species that are causing big ecological and economic damage. Most recent invasive species have entered the Great Lakes via saltie ballast water. The Great Lakes are currently home to 185 invasive species, with a new invasive being discovered every six months. Some of these Great Lakes Invaders have moved to inland lakes.

Not all non-native species become invasive

Humans play a big role in introducing new species (some of which will become invasive) into new habitats. But unlike more traditional notions of pollution, species can transport and reproduce themselves. Animals and plants move around and find places to live, independently of humans. It not like regulating industrial or municipal sources, where there’s a regulatory shut off valve on a waste pipe that can stop a given pollutant from entering the water. With invasives, ultimately–unless we discover and shut off that valve at exactly the right time–we have limited control over species that are doing a fine job with the business of survival.


But, of the large number of species that are introduced into new habitats, few are successful as invaders. Traits that can make an invasive “invasive” include:

Ability to reproduce quickly and/or in great quantity

• Efficiency in getting themselves (or spores, eggs, seeds) distributed
• Growth patterns that enable invaders to out-compete or circumvent native species’ life cycles

Ability to persist in environments because of broad physiological tolerance or quick adaptation

Not all lakes are equally susceptible to invasion by a given species. And the same invasive may not have the same effect on all lakes. Each lake possesses its own unique characteristics—water chemistry, undisturbed shorelines, low nutrient loading—that may lower the risk of potential invasions. Lake Nancy (pictured below left) has had Eurasian water milfoil for years, with minimal impact on the lake ecosystem and recreation. In contrast, Eurasian water milfoil has become a problem for the lake on the bottom right.

Ongoing research is exploring what lake characteristics may make some lakes more habitable to certain species of invasives. This type of research may lead to smart prevention strategies that allow lake managers to assess which invasives may or may not be problematic for a given lake. The best approaches to prevent, contain, manage, or prevent certain species may be yet to be discovered.

Disturbance and Possible Invasions
Many non-native species that become invasive benefit from disturbed habitats. Disturbance simply means an alteration of a habitat's normal state. Some disturbances are natural—flooding, drought, fires, and other changes which may be part of a natural cycle or an extreme event. Some disturbances may be man-made—clearing of shoreland plants, more nutrients entering the lake, scouring or changing of the lake bottom, and increased turbidity (murky water conditions).

Whenever a disturbance occurs, open habitat is created and something will come in to fill the void. More extreme disturbances like flooding or a increase in nutrients over time may change what species can live in the lake and tolerate the new conditions.

Disturbance can create conditions that give an advantage to invasives and suppress natives. When there is a disturbance there is open habitat and a “race” to see what gets there first and grows the most quickly and successfully—this is winner of the invasion.

Invasive populations tend to arise from habitats that are prone to ecological disturbance. Often these invasives thrive in habitats that are in a constant state of disturbance or are able to adapt and tolerate a broad range of environmental conditions (like high pollutants) that natives cannot withstand. While the same native shoreland plants may recover and reclaim their old space, many invasive species possess "weedy" traits that enable them to quickly take advantage of new territory and out compete natives. Our modern day practices of mowing our lawns is a example of keeping an ecosystem in a constant state of disturbance—to the benefit of invasive species no less (grass, dandelions, and clover are all native to Europe)!

Troublesome invasives like Eurasian water milfoil and curly leaf pondweed benefit from nutrient rich waters, and many of our lakes have become watershed collection ponds for fertilizers and sediments. Carp—a hearty invasive deliberately introduced in the 1880's—is tolerant of murky water conditions which frequently accompany algae dominant eutrophic lakes. Carp continue to stir up bottom sediments, which perpetuates disturbance and sends more phosphorus into the water, which in turn feeds more algae blooms. Disturbance benefits these invasives at the expense of natives. 

The results of disturbance are unpredictable. The resulting lake community can be dominated by:

• Species not present prior to the disturbance (an invasion, note this does not necessarily mean a non-native species),
• Species that were dominant before the disturbance,
• Or it might become dominated by species that were present before the disturbance but not dominant

If disturbance brings invasives, equilibrium can be achieved in a variety of ways:

• The invasive can "take over" and establish a new invasive monoculture,
• The system can re-balance as part of a native/invasive system,
• The invasive can exist as marginalized part of the native system

Keeping your shoreline intact is a good way to minimize disturbance and minimize opportunities for invasive species to gain a foothold.
 

Prevention, Containment, Management
Prevention

Prevention is the most cost effective and “easiest” way to deal with AIS. Constant vigilance by citizen volunteers, training on identification of invasive species, and education campaigns can be effective over time. The dedication of citizen volunteers conducting boater education programs like Clean Boats, Clean Waters has led to many citizens taking simple preventative steps when boating and fishing. AIS monitoring and aquatic plant management surveys—often commissioned by lake groups and funded by DNR lake grants—has greatly increased local knowledge about the presence/absence of AIS in lakes. This is critical information to have in the event that an invasive species is discovered in the lake, as it can help quickly assess the extent of the problem and guide lake managers on treatment options.

But no matter how good, prevention is like a sieve. You may keep a lot of stuff out, but eventually something gets through.

Containment

Some invasive species are in the pioneering stage. That is there are a few individuals that have been dropped into a new habitat and are surviving. There may not be enough individuals to have a reproducing population that can be sustained over time. This can mean that the invasive individuals simply die out (the population is self-limiting). It also means small numbers of an invasive over a large area can be hard to discover.

The more established an invasive species gets—the more successfully reproducing populations sustain themselves and then spread to additional territory—the harder it becomes to eradicate an invasive from the landscape. Eventually the line between hard to eradicate and impossible to eradicate gets crossed, and then the option becomes management of the species.

Management

Management can mean a lot of things. It can mean you are managing to prevent further spread to additional water bodies, preserve native habitat, contain an invasive population to a restricted area, or perhaps manage so certain uses (recreational) of the lake are preserved. There may eventually be a decision not to manage. Either the problem caused by the invasive is not severe, or a cost/benefit analysis leads lake decision makers to abandon management. Many groups are investing private (and state) dollars into treating waters for invasives like Eurasian water milfoil, curly leaf pondweed, and carp.
 

Using lake classification for AIS work

Lake classification is a flexible lake management tool that counties may use to organize lakes into similar groups and tailor management approaches to meet the needs of lakes within each class. Traditionally, lake classification has been used primarily to set up different shoreland development standards for different classes of lakes, but it can also be used set up recreational use classes, and potentially AIS management. The lake classification process allows counties to gather data about their lakes’ physical features—such as lake type, size, watershed area, aquatic plant surveys, sensitivity to pollution and other development.

With regard to AIS, basic data gathering like aquatic plant surveys can be valuable to assess the presence/absence of AIS species, ecological susceptibility of certain lakes to invasion by given AIS species, and vectors for the movement of AIS within and into the county. This could result in classifying county lakes in terms of priority lakes to focus AIS prevention resources and targeting resources aimed at managing established populations of invasives.
 

Introduction of non-native species has a long history

North America has been receiving successive waves of non-native species (some of which became invasive) since 1492, when the "old World" of Europe first made contact with the "New World." Colonists brought many familiar species with them (including many domesticated crops and animals). Some non-native species were deliberately brought (horses, cows, cats, honeybees, oats, clover, peach trees, Kentucky bluegrass, etc.), some inadvertently (rats, nettles, dandelions, smallpox, typhoid, etc.). Many species that we may think of as natives, may in fact be old non-natives/invasives that have become an established part of the ecosystem!

Would you recognize the following as non-native species?
   

Old World species were primed to succeed in new habitats. For thousands of years, European agricultural practices helped evolve weeds, sturdy crops, domesticated animals, and the pests and pathogens that co-exist with them. Tilling, animal hooves scratching the earth, growing of food in one place (often in a monoculture), and concentrating people and domestic animals into population centers, provided a constant state of disturbed habitat, and helped evolve organisms that were used to co-existing with each other. When colonists made changes in land use and landscape—such as clearing of forests for crop land—this favored some invasive species over natives.

New World species were less equipped to compete with new invaders and less able to exhibit invasive behaviors themselves when introduced into Old World environments. Unlike many of the Old World plants and animals that established themselves in the New World, not as many New World species were able to compete when they were introduced in Europe. For example turkeys survived, but as a novelty, not as an indistinguishable addition to the European ecosystem, compared to the English song sparrow which now thrives in the U.S. The American Gray squirrel and muskrat stand out as exceptions to this rule. Some items, like sugar from sugar cane, became an important export from the New World, even if they could not survive in the old. Many of North America’s most aggressive weeds could not even get started in Europe.
 

New World species that went to the Old World

More Information:

Link to Aquatic Invasive Species AIS Policy Work Page
University of Wisconsin Sea Grant Institute
Wisconsin DNR Invasives Page
PDF: Disturbances and Invasions
PDF: Watch Your Water Gardens!

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