Lesson 1: Ripple Effects, Invader Species of the Great Lakes

Background

An invasive plant or animal is one that has moved and established outside of its native range and causes harm to the environment, economy, or human health. Invasive species arrive through intentional or accidental human actions. Biologists usually judge the consequences of these impacts based on how much they add to, or detract from, some important human endeavors. They also attempt to examine the effects upon other plant or animal species. Invasive species sometimes have no natural predators in their new locations, and this may allow them to overpopulate an area and reduce native species.

Since the early 1800s, over 180 species of aquatic plants, algae, fish, worms, mollusks, other organisms, and diseases have been introduced into the Great Lakes. It is estimated that about 20% of the 170 or so species of Great Lakes fish are non-native species that were introduced accidentally or intentionally.

A few aquatic invasive species have had very substantial impacts. One such invader to the Great Lakes is the sea lamprey. Common to the ocean waters from Florida to Labrador, sea lamprey swim inland into fresh waters to spawn. Natural barriers, like Niagara Falls, previously prevented them from reaching the rest of the Great Lakes. However, once shipping routes like the Erie and Welland canals were opened up, sea lamprey easily found their way to the Great Lakes, where it decimated populations of native and
stocked fish species.

Many AIS hitched a ride to the Great Lakes region in the ballast of ships. When ships are not loaded with cargo, they take on ballast for better balance, stability, and safety. The use of water as a ballast has replaced the use of sand and stones over the past 100 years or so. Scientists think many of today’s invasive species, such as quagga mussels, round goby, Eurasian ruffe, and spiny waterflea, were sucked up from foreign harbors by powerful water pumps. Ballast tanks are filled with water from the harbors wherever ships are loaded, and then the water is dumped, along with any aquatic organisms present, when ships reach their destination. It is estimated that in the history of the Great Lakes, over 30% of the invader species entered in solid ballast and over 50% through ballast water.

The United States and Canada now require that all ships entering the Great Lakes to discharge their freshwater ballast while still in the ocean, replacing it with saltwater ballast to reduce the introduction of new aquatic invasive species.

There are always trade-offs involved with the accidental or intentional introduction of a species into an ecosystem. Sometimes the impacts are difficult to judge ahead of time. Laws and regulations are intended to force a careful review of pros and cons before the intentional introduction of a new species is allowed. The introduction of a species that will have mostly detrimental impacts is not allowed.

People can help to avoid the spread of AIS by taking precautions. For example, boaters should be careful to rinse the bottoms of boats, bilge pumps, and live wells with clean, heated tap water before leaving lake or river areas. And they should remove aquatic plants that cling to boats and hulls. Ships should always release foreign ballast before entering their destination.