Imagine what a scoop of river water might contain. It might look clear at first glance, but upon closer inspection, you may find some tiny, wiggly creatures that look like insects or worms, known as aquatic macroinvertebrates. These organisms are:
Aquatic – live in water for part of all of their life.
Macro – Small, but large enough to be visible to the naked eye.
Invertebrates – have no backbone.
Mayfly Nymph-Photo by Phil Rowley
Aquatic macroinvertebrates are most well-known for being the main source of food for many different species of fish, as well as many wetland birds. However, these little critters also play a vital role in aquatic ecosystems by managing the distribution and abundance of algae and breaking down waste and plant matter in a waterbody. To understand how aquatic invertebrates can do this, we can split them into groups based on what and how they eat.
These groups are known as functional feeding groups, and there are four main groups:
Grazers
Shredders
Collectors
Predators
Have you ever seen an algae-covered rock with strange, squiggly tracks where the algae has been cleaned off? These tracks were created by grazers—aquatic invertebrates that eat algae and microorganisms like bacteria by scraping them off of rocks and vegetation. Grazers are great at keeping algae in check.
Cased Caddis-Photo by Phil Rowley
Shredders eat large pieces of living or dead plant material by ripping them up with their sharp mouthparts. If you’ve ever wondered what happens to leaves that fall into the river in the fall, look no further; shredders start the first stage of decomposition for these leaves by physically breaking them down into smaller particles that can be consumed by other aquatic invertebrates.
Collectors live by the saying, “One man’s trash is another man’s treasure.” These aquatic invertebrates eat small particles of dead organic matter, or detritus, which include the smaller particles of plant material left behind by shredders, as well as the feces and other waste products from larger animals, like fish and birds. There are two types of collectors: gatherers scavenge for detritus on the bottom of a waterbody, while filterers eat detritus, algae, or other tiny invertebrates that are suspended in the water.
Predators eat other living animals, such as other aquatic invertebrates, small fish, and even tadpoles. Some predators have large jaws to capture and eat their prey. Others use a tubular, sucking mouthpart called a proboscis to pierce the skin of their prey and consume their bodily fluids—they’re like the vampires of the stream!
In aquatic ecosystems, fish tend to steal the limelight, but aquatic macroinvertebrates are interesting and diverse, too! If this quick introduction hasn’t convinced you of how cool these critters are, don’t give up on them yet!
Stonefly Nymph-Photo by Phil Rowley
TUC will be publishing a series of articles highlighting aquatic macroinvertebrates over the next couple of months. Stay tuned!
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