A macroinvertebrate is a living organism that can be seen by the naked eye (macro), and doesn’t have a backbone (invertebrate). The presence or absence of these macroinvertebrates in freshwater ecosystems give us a good indication of water quality.
This Stonefly nymph, found in the Kawharawhara Steam within the bounds of Otari-Wilton’s Bush is missing it’s second cerci (tail) and has gills between.
Some macroinvertebrates are very tolerant of pollutants, while others are extremely sensitive. Therefore macroinvertebrates such as mayflies, stoneflies and caddisfly nymphs can be used as biotic (living) indicators for stream health. An index, called the Macroinvertebrate Community Index (MCI), has been developed for this purpose.
In a healthy stream, it is best to find a diverse range of macroinvertebrates with a high numerical value. Mayfly larvae (pictured below) and stonefly larvae (pictured above) are very sensitive to pollution with a high number they are what we hope to find in a stream to indicate a good water quality. Please view “A user guide for Macroinvertebrate Community Index” to gain an in depth understanding of the MCI and its applications.
These two photos are both of mayfly nymphs taken during the pop up Open Lab session at Zealandia. Notice their cerci (tails) count three. There are four types of nymphs we can classify them by how they mobilize themselves. The first photos is of a crawler and the second a swimmer.