Water: Masterbug Theatre
NPS Kids Pages
There is a whole world of life in rivers and lakes. Some of the tiny animals living in the water are benthic, meaning they live in the bottom of the waterbody. Some are macroinvertebrates because they are large and easy to see (macro) and because they have no backbone (invertebrate). The most common of these creatures include insects, clams, snails, crayfish, and worms. Some live their whole lives in the water, and others leave the water as adults to feed and reproduce.
Macroinvertebrates are important as food to all the creatures living in the water. Some are considered by scientists to be indicator species and are a way of telling whether or not a river or lake is polluted. In rivers, macroinvertebrates live attached to rocks and plants where there is fast-flowing water. They are good indicators of water quality because they do not move around and are easy to collect. The moving water gives them food and oxygen. If the water is polluted, there is less food and oxygen for the aquatic macroinvertebrates. If the water has pollutant-intolerant macroinvertebrate species in it, that is a good indication that the water is clean and of high quality. If there are mostly pollutant-tolerant macroinvertebrates in the water, there is a chance that the water is polluted and only those types of species can survive.
In lakes, where there is not fast-flowing water, the dynamics are slightly different. Indicator species in rivers are not necessarily as "telling" in lakes where the waters are relatively still.