The following article was written by Jim Grazio, Ph.D., Great Lakes Biologist with the Pennsylvania Department of Environmental Protection and was originally included in the Summer/Fall 2020 edition of the "Tracking Invasive Species with Pennsylvania iMapInvasives" newsletter.
View of the Great Lakes. Credit: Pixabay
The Laurentian or North American Great Lakes have been described as one of the most heavily invaded ecosystems in the world. Sturtevant et al. (2019) provided a recent and comprehensive review of over 180 non-native aquatic species which have become established into the Great Lakes. While most of these species are harmless, a subset of these nonindigenous species cause environmental and/or economic harm - these are aquatic invasive species (AIS). Some, like the sea lamprey (Petromyzon marinus) and zebra/quagga mussels (Dreissena polymorpha & D. bugensis) have had truly extraordinary impacts since their introduction - dramatically altering food webs, contributing to the collapse of important fisheries, and causing total economic impacts estimated to exceed $1 billion each year.
Tens of millions of dollars are spent annually to suppress sea lamprey populations and prevent zebra mussels from clogging water pipes. However, for virtually all AIS, there is no way to eliminate these highly destructive species from the lakes, and their impacts continue to this day.
Photos in slideshow: Quagga mussels, zebra mussels, round goby, and sea lamprey. Photo credits at the bottom of this blog post.
INVASION PATHWAYS
There are many ways that nonindigenous species are spread from their donor to recipient regions. Two of the most important path of entry into the Great Lakes have been the discharge of ballast water (and the aquatic organisms it contains) from trans-oceanic shipping and the construction of man-made interconnections and canals.
Zebra mussels and a small, yet aggressive, fish known as the round goby (Neogobius melanostomus) are examples of highly destructive AIS that were introduced into the Great Lakes through ballast water releases in the 1980s and 1990s. The rate of AIS introduction via this pathway into the Great Lakes has slowed since the implementation of mandatory open-ocean ballast water exchange rules in 2006. However, the risk of further introductions via ballast water discharges still exists since ballast water exchange isn't 100% effective at removing organisms from a ship's tanks.
Canals and waterway interconnections were among the first pathways for the spread of AIS. The installation of locks and dams on the St. Lawrence River, designed to allow for the passage of oceanic freighters, also allowed for the entry of coastal fishes like the parasitic sea lamprey from the Atlantic Ocean. Since the Chicago Sanitary and Ship Canal was built, the Great Lakes are hydrologically connected to the Mississippi River basin, allowing for the passage of AIS between these two waterways.
(Top): Unionid mussel covered in invasive zebra mussels. (Bottom): Round gobies. Credit (both): PA DEP
FUTURE THREATS
As long as hydrologic interconnections remain and people continue to move vessels and equipment between bodies of water, the risk for further introduction of AIS will continue to persist. Even today, the "near perfect" aquatic weed hydrilla (Hydrilla verticillata) and invasive Asian carp species are poised to invade the Great Lakes through existing canals and interconnections.
Some researchers fear an "invasional meltdown", whereby each successive invasion further destabilizes an ecosystem that has already been highly altered by AIS. Since there is no practical way to eliminate biological organisms from an interconnected Great Lakes system containing 20% of the world's surface freshwater, the prevention of further introductions and spread of AIS into and within the Great Lakes is essential to preserve both the natural heritage and economic vitality of the Great Lakes region.
ADDITIONAL RESOURCES
Jim Grazio. Credit: PA DEP
ABOUT THE AUTHOR
Jim Grazio is the Supervisory Great Lakes Biologist for the Pennsylvania Department of Environmental Protection. He is the agency's lead scientist on Great Lakes issues and is a past Chair of the Great Lakes Panel on Aquatic Nuisance Species.
Jim holds a Ph.D. in Wildlife and Fisheries Science from Penn State University and is an adjunct faculty member with Penn State Behrend's School of Science.
Jim can be reached via email at jagrazio.pa.gov.
Photo Credits in Slideshow:
Quagga mussels in a laboratory setting. Credit: Rebekah D. Wallace, University of Georgia, Bugwood.org (link)
Zebra mussel. Credit: Amy Benson, USGS, Bugwood.org (link)
Zebra mussels. Credit: Julie Mida Hinderer, Bugwood.org (link)
Round goby. Credit: Eric Engbretson, USFWS, Bugwood.org (link)
Round goby. Credit: USGS, Bugwood.org (link)
Sea lamprey. Credit: USFWS, Bugwood.org (link)
Sea lamprey. Credit: Great Lakes Fishery Commission (link)