Macroinvertebrate

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The term macroinvertebrates is traditionally used to refer to aquatic invertebrates including insects (e.g. larval Ephemeroptera and Trichoptera), crustaceans (e.g. amphipods), molluscs (e.g. aquatic snails) and worms (e.g. Platyhelminthes), which inhabit a river channel, pond, lake, wetland or ocean. Historically, their abundance and diversity have been used as an indicator of ecosystem health and of local biodiversity. They are a key component of the food chain.

Most indices that are used to determine water quality rank the various forms of benthic macroinvertebrates with respect to pollution sensitivity. The presence of pollution sensitive macroinvertebrates indicates that the body of water is healthy. Alternatively, the excessive presence of pollution tolerant macroinvertebrates indicates poor water quality. Ideally, a healthy body of water will hold an abundant and diverse macroinvertebrate population.

The macroinvertebrates traditionally seen as being pollution sensitive include: mayflies (Ephemeroptera), caddisflies (trichoptera), and stoneflies (Plecoptera). The macroinvertebrates that have been traditionally considered pollution tolerant include: aquatic worms (Oligocheata), leeches (Hirudinea) and blood worms (Chironomidae). Flow, food, habitat and water quality are the primary determinants of macroinvertebrate abundance and diversity. Food sources include phytoplankton, biofilms (i.e. the layers of bacteria or other micro-organisms that cover submerged surfaces) and terrestrial organic material (e.g. leaves) that enter the water from the riparian vegetation. Major predation occurs from other macroinvertebrates and fish. Key habitats for macroinvertebrates are the benthic sediments, aquatic vegetation and woody debris. Salinity, temperature, dissolved oxygen, and turbidity have a significant impact.