Macroinvertebrates are good indicators of biological quality, as they are easy to sample and require only relatively simple taxonomic identification. They are also widespread in most areas where water is present.
These creatures are used as quality indicators in the majority of rivers in the world, as they respond to environmental changes in a very direct manner and they facilitate the assessment of any disturbances or modifications in rivers and wetland areas.
If water quality is good, there are a lot of species, however, if it is bad, there may be a lot of individual animals, but only a few species.
Aquatic macroinvertebrates are large animals (over 500 micrometres and without an internal skeleton) that live in continental aquatic ecosystems (rivers, ponds, lakes and estuaries, etc.).
They are distributed throughout different environments in bodies of water: under stones, in calm waters, in rapids, and waterfalls, among underwater plant life, etc.
They include aquatic and semi-aquatic organisms as well. One example of semi-aquatic organisms are heteropterae – more commonly known as pond skaters; these creatures walk, slide and jump on the water’s surface. There are in fact very few macroinvertebrates that are truly aquatic throughout their entire lives, such as sponges, molluscs and crabs.
Most, especially insects, caddis-fly larvae and dragonflies, live in the water only during their larval or nymphal phase.
Freshwater jawless leech
Ostracod or seed shrimp
Small squaregill mayfly
Lesser water boatman
Skimmer or percher
Predaceous diving beetle
Long-toed water beetle
Long-horned caddis fly
Net-spinning caddis fly
Free-living caddis fly
Finger-net caddis fly
Illustrations: © Toni Llobet