What Are Macroinvertebrates?

Freshwater benthic macroinvertebrates, usually simply called macroinvertebrates, are small animals that live in the water. They have three parts to their name: “Benthic” refers to the bottom part of a body of water, “macro” means that we can see it with our naked eye, and “invertebrate” means that it has no spine, or vertebrae. So, a benthic macroinvertebrate is an organism that lives at the bottom of streams, rivers, lakes, and ponds for part of its life, can be seen with the unaided eye, and has no backbone. Some macroinvertebrates have three life stages, while others have four. If the life cycle has four stages, it is called complete metamorphosis. If it only has three stages, the life cycle is called incomplete metamorphosis. The stages of complete metamorphosis are egg, larva, pupa, and winged or aquatic adult. The stages of incomplete metamorphosis are egg, nymph, and flying adult. Adult macroinvertebrates sometimes leave the water but live near it, and others continue to live in the water. Macroinvertebrates are a vital food source for fish, turtles, wading birds, and small mammals.

They are well suited to live in water, and many have interesting adaptations that allow them to thrive underwater. Caddisfly larvae build mobile protective cases out of stones, leaves, and small sticks to keep themselves safe. Mayfly nymphs have large gill areas to help them breathe. Predaceous diving beetles carry small bubbles of oxygen at the ends of their abdomens from the surface to use to breathe while underwater.

Another interesting thing about macroinvertebrates is that they can be used as an indicator of health for a body of water. This is because some species of macroinvertebrates are more sensitive to environmental stressors than others. Rivers, streams, and ponds with a variety of macroinvertebrates are considered healthy.

photo by Ian Alexander: https://upload.wikimedia.org/wikipedia/commons/5/50/Mayfly_nymph_dorsal_view_wing_buds_paired_gills.JPG

photo by Michael Palmer: http://www.photorasa.com

A mayfly nymph on the left; a mayfly adult on the right. Notice the gills along the back end of the nymph, this is how the animal gets oxygen from the water, similar to a fish.

Macroinvertebrates need dissolved oxygen in order to breathe in the water, just like fish. Dissolved oxygen references the microscopic bubbles of oxygen gas that are mixed with the water for aquatic creatures to breathe. Dissolved oxygen is sometimes measured in parts per million (ppm). Most fish do well in water with 5ppm of dissolved oxygen or higher. Pollution can cause water temperatures to rise, which reduces the amount of dissolved oxygen in the water.  So, pollution decreases dissolved oxygen levels, making it hard for macroinvertebrates to breathe. A healthy body of water will have dissolved oxygen levels that are at or above 5ppm.

Macroinvertebrates as Indicators of Water Quality

There are many different types of macroinvertebrates, all with different sensitivities to temperatures, the amount of dissolved oxygen in the water, and pollution levels. Macroinvertebrates require similar dissolved oxygen levels as fish, but some species, such as mayflies, caddisflies, and stoneflies, need low temperatures and high levels of dissolved oxygen to survive. If you look for macroinvertebrates and find mayfly and stonefly nymphs in a stream, you can conclude that the stream is fairly healthy because those organisms could not survive otherwise. Those species are considered to be sensitive to pollution.

There are also species that are somewhat tolerant of pollution, like dragonflies, damselflies, and crayfish. These organisms do not need as much dissolved oxygen or as cool of temperatures as those that are sensitive to pollution and can stand a small amount of pollution in the water. If one were to find dragonfly nymphs in a stream but no mayfly, caddisfly, or stonefly nymphs, that could be an indicator that the stream has some pollution.

Finally, there are species that are tolerant of pollution. Some of these species are midges, backswimmers, and aquatic worms. These organisms can withstand a moderate amount of pollution, can live in warmer water, and do not need as much dissolved oxygen to survive. So, if one were to find many midge larvae and aquatic worms in a stream and little else, this would indicate that the water there is fairly polluted. Sometimes, tolerant macroinvertebrates can be abundant in degraded waters since they are not competing with others for resources like food and shelter.

Below is a list of several species of macroinvertebrates with their varying tolerances of pollution.

Pond Investigators Program

Clay Pit Ponds State Park Preserve’s education team has done several surveys of the ponds within the park to get an idea of the water’s health. Clay Pit Ponds is the only NY state park on Staten Island; the park contains 265 acres of forest, fields, wetlands, and five ponds. The park offers an educational program all about macroinvertebrates called Pond Investigators.  In this program, students learn to identify macroinvertebrates, understand them as an indicator of water quality, and conduct a survey of one of the ponds. The most recent survey was conducted in Goode’s Pond, which is located along the Clay Pit Pond trail (orange markers). To survey for macroinvertebrates, the students and the Clay Pit Ponds education team scraped the bottom substrate of the pond, including some aquatic vegetation, with a dip net. Off to the side, a tub was partially filled with pond water. The collections from the dip net were transferred into the tub, and any macroinvertebrates found were placed into separate cups. This was repeated three times, and then the students recorded their findings.

Goode’s Pond is very close to the West Shore Expressway, which makes it an interesting pond to study due to the likely presence of runoff pollution from the highway. These surveys were completed along with water quality tests to check pH, dissolved oxygen, water temperature, and salinity. During these surveys, the Clay Pit Ponds education team and students found damselfly nymphs, dragonfly nymphs, backswimmers, midge larvae, crane fly larvae, black fly larvae, mosquito larvae, aquatic beetles, snails, and aquatic worms. While no pollution sensitive species have been found, which would indicate cleaner water, the samples did include many species that do not tolerate heavily polluted water. From this study we learned that the water in the ponds is in fair to moderately good condition at this time. With continued efforts to clean up in and around the ponds, we can keep this important habitat clean and preserve opportunities to see a diversity of wildlife, from dragonflies to great blue herons.

If you would like to help Clay Pit Ponds State Park Preserve improve the health of its ponds, join in for the National Public Lands Day Clean-Up on Saturday, September 24^th from 10:00AM to 1:00PM! Participants will clear litter from the highways that border the park to prevent it from being washed into the ponds. The clean-up will start at the Nature Interpretive Center located at 2351 Veterans Road West, Staten Island, NY. All ages are welcome! Please RSVP by contacting Emily Becker at emily.becker@parks.ny.gov or (718) 605-3970 x201.

Post by Mikey Bard, SCA/Americorps Member serving as Assistant Environmental Educator at Clay Pit Ponds State Park Preserve