Marvelous Macroinvertebrates

What is it that is so mesmerizing about water? Watching a stream flow by or the ripples on a pond seems to take us to a place of peace. But, what if we look closer, look down into the water? Perhaps we can see the substrate below. There is a whole world under the water's surface. What creatures might inhabit this mysterious realm? Pick up a rock from the streambed or a clump of leaves pressed together by the current, and you are likely to find some aquatic macroinvertebrates clinging or crawling on the objects in your hand.

What are aquatic macroinvertebrates, and why are they important? An aquatic organism is one that lives in or around water. The word macro refers to an item that is large enough to be visible to the naked eye. Invertebrates are organisms that do not have a backbone or spinal column - no internal skeleton here. There are many types or, taxa, of aquatic macroinvertebrates from mollusks to worms to crustaceans to insects. Each type has specific conditions under which it will be able to thrive and reproduce. That is what makes these sentinels crucial to the efforts to protect our water resources. They can give us an indication of the health of the body of water we are observing. Aquatic macroinvertebrates are like the canary in the coalmine, warning us of troubled waters.

According to the US Environmental Protection Agency, aquatic macroinvertebrates are good indicators of stream quality because:

• They are affected by the physical, chemical, and biological conditions of the stream.
• They can't escape pollution and show the effects of short- and long-term pollution events.
• They may show the cumulative impacts of pollution.
• They may show the impacts from habitat loss not detected by traditional water quality assessments.
• They are a critical part of the stream's food web.
• Some are very intolerant of pollution.
• They are relatively easy to sample and identify.

One of the reasons for their status as indicators of water quality is the length of time some aquatic macroinvertebrates spend in the water. Some are life-long residents, such as crayfish and mussels. Others, such as many in the insect group, live in the water during their immature stages. Certain insects live in the water only a few weeks as larvae. Others make their home there for several years before becoming adults and joining the terrestrial world. Whereas testing of physical and chemical parameters gives us a snapshot of a moment in time for that body of water, collecting data on macroinvertebrates gives us a long-term view of the health of the water.

Macroinvertebrates have been divided into several groups based on their pollution tolerance. The best water quality is often indicated by the presence of EPT -Ephemeroptera (mayflies), Plecoptera (stoneflies), and Tricoptera (caddisflies). There are other macroinvertebrates that fall into this intolerant category, but if the "big three" are present, it is a good sign of clean water.

The next group is moderately tolerant of pollutants. Included in this group are dragonfly and damselfly nymphs, scuds, and cranefly larvae, among others.

Macroinvertebrates that are fairly tolerant of pollution include midge larvae, leeches, planaria, and blackfly larvae.

Two macroinvertebrates that can tolerate a significant amount of pollution are aquatic worms and blood midge larvae.

The presence of macroinvertebrates that are more pollution tolerant among a population of those that are less tolerant does not indicate poor water quality, but just that the more tolerant species are able to live under a broader range of conditions. Scientists, including citizen scientists, look for changes in the composition of populations of macroinvertebrates over time. If changes seem persistent, analysis may reveal changes in environmental conditions, either positive or negative. Ongoing monitoring of aquatic populations is very valuable not only to gain a clearer picture of water quality, but also in overall environmental oversight.

Since 2017, the Berks County Master Watershed Stewards have been collecting chemical, physical, and biological data at Nolde Forest Environmental Education Center. Data is reported to DCNR as well as being uploaded to the GLOBE system. Various other sites are being monitored as well.

Note: The Pennsylvania Fish and Boat Commission consider Macroinvertebrates fish bait. A valid fishing license is required for anyone age 16 or older to collect macroinvertebrates, even if they are returned to the water alive (which they should be).

References

University of Notre Dame: Bios 21202. Pollution tolerance index. Retrieved April 15, 2020

PA SeaGrant. Identification of freshwater invertebrates. Retrieved April 15, 2020

US EPA, O. (2013, January 29). About the office of water [Overviews and Factsheets]. US EPA.

Voshell, J. R. (2002). A guide to common freshwater invertebrates of North America. Newark, OH: McDonald & Woodward Pub.