Macroinvertebrates in the Mississippi River Basin

A NWNL NextGen Blog by Johanna Mitra, Stony Brook University.

This is the latest post to our NWNL NEXTGEN BLOG series. Since 2007, NWNL has supported watershed education with college internships and blogging opportunities. Our NWNL NEXTGEN BLOG series posts only student essays; sponsors a forum for its student contributors; and invites student proposals to write on watershed values, threats and solutions.

Johanna Mitra lives in New York City and is an undergraduate student at Stony Brook University. She is majoring in Ecosystems and Human Impact, with a focus on wildlife conservation, and minoring in geospatial science. This is the first in her NWNL Nest-Gen Blog series on the importance of macroinvertebrates in aquatic ecosystems.

A few weeks into one of my freshman-year environmental labs, our professor loaded the entire class onto a bus along with a collection of nets and waders. In twenty minutes, we arrived at a nearby stream, where our professor revealed our mission: we would be assessing the water quality by collecting macroinvertebrates.

While this term itself was new to me then, I’d seen macroinvertebrates before in the form of dragonflies, crayfish and mussels, to name a few. We suited up in our waders; armed ourselves with nets; and headed out into the stream. After a half an hour of turning over rocks and stirring up silt in the stream bed, our nets revealed the incredibly diverse, but mostly hidden, world of these freshwater creatures.

“Students stir up rocks to knock stream insects into the net.” USFWS/Southeast. This work is licensed under a Creative Commons Attribution 4.0 International License.

What are Macroinvertebrates?

Almost every stream, river, pond, lake or other freshwater body of water is home to macroinvertebrates. Some, like crayfish, mussels and clams consider aquatic ecosystems home for their entire lives. Others more commonly seen on the ground such as dragonflies, mayflies and beetles actually begin their life cycles as aquatic larvae, living among the rocks and vegetation in the water.[mfn]U.S. EPA[/mfn] These animals are big enough to be seen without the help of a microscope, hence “macro”, and also don’t have a backbone, classifying them as invertebrates.

A small sampling of the diversity to be found within macroinvertebrates.[mfn]West Virginia Department of Environmental Protection[/mfn]

Although relatively small, their importance to aquatic ecosystems is massive. While not only serving as a major food source for the fish, bird, and amphibian species sharing their habitat, macroinvertebrates play an integral role in nutrient cycling through their feeding behaviors.[mfn]U.S. National Park Service[/mfn] Their ability to consume both living and decaying plant or animal material, such as algae or fallen leaves helps to maintain healthy levels of nutrients in the water, which other species rely on as well.[mfn]West Virginia Department of Environmental Protection[/mfn] In fact, their sensitivity to the chemical, physical and biological composition of their habitat makes them incredibly useful as indicators of water quality. Their abundance, or lack thereof, in a stream or lake can suggest changes in levels of pollution, temperature, heavy metal accumulation and other variables affected by human activity that can sometimes go undetected in routine water quality checks.[mfn]Wallace, J. Bruce, and Jackson R. Webster[/mfn]

Mayflies in the Mississippi

One of the characteristic macroinvertebrates of the Mississippi River is the mayfly. Every summer, massive swarms of mayflies take to the air from the water, where they have spent about a year maturing as mayfly nymphs. Their presence year after year has served as both a strong indicator of the Mississippi’s health and an important food source for other species in the river.

“Mayfly Swarm” by forstwalkr. This work is licensed under a Creative Commons Attribution 4.0 International License.

However, in recent years the size of mayfly swarms has been decreasing indicating that the Mississippi’s quality has degraded significantly. A study from the Proceedings of the National Academy of Sciences revealed that since 2012, the northern Mississippi mayfly population has decreased by as much as 50%.[mfn]Main, Douglas[/mfn] What is the suspected culprit of their decline? An increase in synthetic chemicals use namely, pesticides, insecticides and fertilizers by the agricultural industry in areas within the Mississippi River basin. Runoff of these chemicals from farmland into tributaries significantly alters the water’s composition and triggers an increase in harmful algae blooms (HABs), both of which creates unsuitable habitat for macroinvertebrates due to their sensitivity to such changes.A decline in the mayfly population can potentially translate to a decline in other insect-eating species, as they are a significant energy source for those species higher up on the food chain.[mfn]Katz, Brigit[/mfn]

“Lake Erie HABs Aug 2017” by NOAA Great Lakes Environmental Research Laboratory. This work is licensed under a Creative Commons Attribution 4.0 International License.

Conservation Efforts

While it can be difficult to pinpoint the exact sources of the influx of synthetic chemicals into the Mississippi River, efforts can still be taken to mitigate their effects and to restore the water quality. Years ago, the EPA set in motion a plan to reduce nitrate levels—an increase of which is behind the rise in algal blooms and other water pollution—by 45% in the Mississippi River Basin. These efforts led by state and local governments, coupled with a tightening of restrictions on the labeling of pesticides and fertilizers, raising awareness of the environmental impact of runoff pollution and shifts to more sustainable agricultural practices will lead the way for water quality improvement and the return of healthy mayfly and other macroinvertebrate populations to the Mississippi River Basin.[mfn]Howard, Brian Clark[/mfn]


“Aquatic Macroinvertebrates – Ecological Role.” U.S. National Park Service, n.d. Accessed on May 29th, 2020 by JM.

“Biological Monitoring.” West Virginia Department of Environmental Protection, n.d. Accessessed on May 30th, 2020 by JM.,Biological%20Monitoring,the%20State’s%20streams%20and%20lakes.&text=Fish%20community%20sampling%20in%20streams,WAB%20biological%20monitoring%20since%202006.

Howard, Brian Clark. “Mississippi Basin Water Quality Declining Despite Conservation Efforts.” National Geographic, April 12, 2014. Accessed on June 1, 2020 by JM.

Katz, Brigit. “Massive Mayfly Swarms are Getting Smaller – and That’s Bad News for Aquatic Ecosystems.” Smithsonian Magazine, January 23, 2020. Accessed on June 1, 2020 by JM.

Main, Douglas. “Mayfly numbers drop by half since 2012, threatening food chain.” National Geographic, January 20, 2020. Accessed on May 30, 2020 by JM.

Wallace, J. Bruce, and Jackson R. Webster. 1996. “The Role of Macroinvertebrates in Stream and Ecosystem Function.” Annual Review of Entymology 41(1): 115-39. Accessed on May 31, 2020 by JM.

2 thoughts on “Macroinvertebrates in the Mississippi River Basin

  1. Wonderful blog, and beautifully written, Thank you! One question: how was the health of the local stream, which the class visited? And the quality of water? Sincerely – S

    1. Thank you for your kind comment! We ended up collecting quite a diverse array of macroinvertebrates from that stream, which was our first indicator of good water quality. In taking various other measurements like the pH of the water, the temperature, and dissolved oxygen levels, we were able to confirm that the stream was a healthy aquatic ecosystem!

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