 Freshwater macroinvertebrates include many tiny animals that live on and under the rocks, on the water plants or on bits of wood lying in a stream, and they also include large species like freshwater crayfish and freshwater mussels. These animals belong to a wide range of groups including insects, crustaceans, molluscs, worms, leeches and anemone-like hydroids. The name macroinvertebrates is used to describe animals without backbones, which can be seen without the help of a magnifying glass or microscope. Many macroinvertebrates are the juvenile life stage of terrestrial flying insects (such as the larvae of mosquitoes and caddis flies, and the nymphs of mayflies, stoneflies and dragonflies). New Zealand’s macroinvertebrate communities differ from those of other countries. There is poor representation or absence of some invertebrate groups, a high degree of speciation in other groups, a large number of primitive species and a high level of endemicity. New Zealand streams have a unique composition of macroinvertebrates with many endemic species and genera. All Ephemeroptera (mayfly) genera and three genera of Plecoptera (stoneflies) are found only in New Zealand. Diptera (true fly) and Trichoptera (caddisfly) faunas are diverse in New Zealand compared with the Northern Hemisphere.
Macroinvertebrates in our streams are an important part of the food web, being a major food for our native fish. They also provide us with an idea of the quality of water and habitat of the stream. Lots of stream invertebrates have specific habitat requirements. We know which species require cool water and high dissolved oxygen levels, and which species are resistant to road runoff. Generally, an abundance of mayfly and stonefly larvae is a good sign. This is because most of these species require cool water and high dissolved oxygen levels (conditions usually found in relatively natural streams). Animals such as snails, worms and midges are much more tolerant of poor water quality, and will be found in most streams.
The MCI (Macroinvertebrate Community Index) is a tool that freshwater ecologists use to rate “health” of a stream.
For further information regarding the Macroinvertebrate Community Index see: http://www.qp.org.nz/uploads/best_practice/pubs/ministry_for_the_environment/3250.pdf
 Identification and taxonomy
Living organisms are classified according to their taxonomy. At present most authorities classify all living and extinct organisms into either a five-kingdom system - Animalia, Plantae, Monera, Fungi, and Protista. Macroinvertebrates are all animals, in the Animalia Kingdom. This is then divided into further groups – Phylum, sub-phylum, class, order, family, genus and species. The following table is a summary of the main groups of invertebrates found in freshwater streams.
|
Macroinvertebrate Group |
Phylum |
Subphylum |
Class |
Order |
|
Mayfly |
Arthropoda |
|
Insecta |
Ephemeroptera |
|
Stonefly |
Arthropoda |
|
Insecta |
Plecoptera |
|
Caddisfly |
Arthropoda |
|
Insecta |
Trichoptera |
|
Dobsonfly |
Arthropoda |
|
Insecta |
Megaloptera |
|
True fly |
Arthropoda |
|
Insecta |
Diptera |
|
Dragonfly (and Damselfly) |
Arthropoda |
|
Insecta |
Odonata |
|
Beetle |
Arthropoda |
|
Insecta |
Coleoptera |
|
Bug |
Arthropoda |
|
Insecta |
Hemiptera |
|
Shrimps, crayfish, crabs, amphipods, isopods, water fleas, copepods and others |
Arthropoda |
Crustacea |
|
|
|
Snails |
Mollusca |
|
Gastropoda |
|
|
Bivalves |
Mollusca |
|
Bivalvia |
|
|
Leeches |
Annelida |
|
Hirudinea |
|
|
Worms |
Annelida |
|
0 |
|
|