The Great Lakes are constantly invaded by non-native species. What are the worst of these invasive attackers and what can be done to stop them?
Invasive species have lived among us since European people first came to the Great Lakes region and we are still discovering new invasive species and combatting their effects on our native species today.
The Great Lakes saw a surge in invasive species when commercial passage from the Atlantic Ocean to the Great Lakes, via the St. Lawrence Seaway, opened up in the 1950s. Incoming ocean-going vessels, and an increase in human activity, brought in many exotic organisms from fish, mollusks, algae, and plants. Now, more than 140 invasive species inhabit the Great Lakes. Many state and local agencies are working to discover new invasive species, stop the spread of those currently in the region, and prevent new invasions in the future.
Zebra mussels are one of the most detrimental and damaging of the Great Lakes invasive species. These small mussels illustrate how easily invasive species can enter our Great Lakes. Zebra mussels were first discovered in Lake St. Clair in 1988 after being brought over in the ballast tank water of a transoceanic vessel coming from the Caspian region to the Detroit area. Very quickly, the zebra mussel established itself throughout all of the Great Lakes and many of the river systems in the surrounding regions.
Now, zebra mussels wreak havoc throughout most of the Upper Midwest. They gather in dense colonies completely covering surfaces, clogging pipes, and damaging boat engines. The mussels also filter water at an extreme rate, with each mussel able to filter up to a quart of water each day. This filtered water is devoid of the nutrients that other species depend on.
Finally, the zebra mussels literally smother native mussel species (like the northern riffleshell) to death by attaching to them until they starve. As the zebra mussels continue to spread, efforts to repel them have seen moderate success in the Great Lakes region -- encouraging residents and environmental agencies alike.
Non-native phragmites, also known as common reed, is an invasive grass species brought over from Europe to the Midwest in the 19th century. Although native phragmites live in the Great Lakes region, the non-native variety grows much faster and more aggressively, both above and below ground, than the original inhabitants.
This accelerated growth creates such dense areas of phragmites that native species and wildlife habitat is crowded out. Rapid growing, non-native phragmites are particularly tough on wetlands. Invasive phragmites also cause economic impacts as property values, views, and shorelines are reduced due to their rapid expansion.
These phragmites are now found throughout the Great Lakes region. Removal of invasive phragmites can be difficult as native phragmites often grow among them and removing them can be detrimental to the ecosystem. Typically, invasive phragmites removal is a process that requires several treatment steps over the course of a few years. Currently in Michigan it is illegal to posses live invasive phragmites unless it is for specimen identification or lawful removal.
The Asian carp has gained notoriety for its aggressive invasion of the Mississippi River system. Asian carp consist of five subspecies which are all extremely voracious, can grow up to 100 pounds, and are very prolific reproducers which allows them to rapidly take over any habitat it establishes itself in.
Asian carp are believed to have entered the Mississippi River system in the early 1990s. Although Asian carp have not yet invaded the Great Lakes, they are very close. Their main entryway into the Great Lakes would likely be through the Illinois River and the Chicago Sanitary and Ship Canal (CSSC) into Lake Michigan.
Should they become established in the Great Lakes, the environmental and economic loss would be heavily felt throughout the entire region. Asian carp have incredible appetites and are nonselective feeders -- able to consume a wide variety of food at a rate of two to three times their body weight. This feeding frenzy would certainly out-compete the native fishes of the Great Lakes.
The competition could potentially wipe out many native fish, plants, and mollusk species. The resulting economic impact could affect fisheries and industries throughout the Great Lakes. Current measures to stop the Asian carp from getting into the Great Lakes include, but are not limited to, an electric dispersal barrier system in the CSSC, an Asian Carp Regional Coordinating Committee (ACRCC) that brings groups together for effective monitoring and removal of Asian carp, research of sound barriers, and campaigns encouraging local harvesting. For now, the carp are being kept at bay.
The Great Lakes are five interconnected lakes that account for 21 percent of the world's surface freshwater. They are a national treasure and, like all treasures, need to be cared for and protected. Through increased awareness and proactive measures, invasive species can be repelled so we can all enjoy great times on the Great Lakes for many years to come.