Benthic macroinvertebrates

Benthic macroinvertebrates are organisms without backbones that inhabit the bottom substrates (for example, sediments, debris, logs, macrophytes, and filamentous algae) of their habitats, for at least part of their life cycle (Rosenberg and Resh 1993). Macroinvertebrates are visible to the naked eye and are retained by mesh sizes greater than or equal to 200 to 500 micrometers. Benthic macroinvertebrates include insect larvae, annelids (leeches), oligochaetes (worms), crustaceans (crayfish and shrimp), mollusks (clams and mussels), and gastropods (snails). Insect larvae tend to be the most abundant benthic macroinvertebrates in freshwater aquatic ecosystems.

As benthic macroinvertebrates tend to remain in their original habitat, they are affected by local changes in water quality. Some are capable of tolerating higher loads of pollution than others. Thus if the pollution is severe, or is moderate but sustained over time, the whole community structure may simplify in favor of tolerant species. Although the abundance of certain species may increase, the diversity, and species richness (the number of different species in a given area) decreases. By assessing indicator species, diversity, and functional groups ofof the benthic macroinvertebrate community, it is possible to determine water quality.

There are four feeding groups of macroinvertebrates: shredders, filter-collectors, grazers, and predators (KY, 1995). Shredders such as stoneflies (plecoptera) feed on plant material and some animal material, which is generally dead, and break it into smaller particles through their feeding and digestive process. Collectors, such as caddisflies (trichoptera) and blackflies (diptera), feed on this fine particle material which they filter from the water. Grazers, such as snails and beetles, feed on algae and other plant material living on rocks and on plant surfaces. Predators such as dobsonflies (magaloptera) or dragonflies (odonata) feed on other macroinvertebrates. Individual species may be generalists, and fit into more than one of these groups (as opposed to specialists).

Note: except where otherwise indicated, the source is (De Lange 1994).

Macroinvertebrates dominant in clean waters

Although water resources with high water quality generally have diverse and rich macroinvertebrate fauna, certain pristine environments have low diversity of macroinvertebrate fauna because of the cold temperature and/or relatively low nutrient levels (Peckarsky et al. 1990). Headwaters and headwater streams may have only two dominant species. Although all classes of invertebrates may be found in headwater streams, crustaceans, caddisflies, leeches, mollusks, flatworms and blackflies tend to be found in such environments (De Lange 1994; Peckarsky et al. 1990).

The majority of macroinvertebrates are found in the riffles of streams. (KY, 1995). Riffles range from uneven bedrock to cobbles to boulders. The optimum riffle area is caused by gravel (1 inch) to cobbles (10 inches). The flow of water over these areas provides plentiful oxygen and food particles. Riffle-dwelling communities are made up of macroinvertebrates that generally require high dissolved oxygen levels and clean water. Most are intolerant of pollution.

Insects (Insecta) Stonefly larvae (Plecoptera) Stoneflies require high dissolved oxygen concentrations and tend to be found in cold, flowing water with a gravel or stone bottom. Some species may be found along lake shores with wave action (Peckarsky et al. 1990). Stonefly nymph groups may be shredders or predators. They may be specialists or generalists (Peckarsky et al. 1990). Dobsonfly larvae (Megaloptera) Generally found in the mud (unconsolidated bottoms) of lakes and wetlands but they can be found in any water type. With the exception of the wetland species, dobsonflies are generally found in well-oxygenated lakes and streams (Peckarsky et al. 1990). Dobsonflies are predators, feeding on other aquatic insects, annelid worms (oligochaetes), crustaceans, and mollusks (Peckarsky et al. 1990). Snipe fly larvae (Diptera Athericidae) Snipeflies will only inhabit the bottoms of very clean, flowing water types. Water spider (Argyroneta aquatica) Water spiders require waters with high oxygen levels lacking pollution. Mayflies (Ephemeroptera) Mayflies are most abundant in cool, unpolluted, headwater streams but they may be found in standing (lentic) water as well. They prefer clean water and an average oxygen supply, but some species can tolerate low dissolved-oxygen levels (e.g. Callibaetis spp.) (Peckarsky et al. 1990). Mayfly nymphs tend to be grazers, feeding on algae or detritus (Peckarsky et al. 1990). Caddisfly larvae (Trichoptera) Generally caddisfly larvae are found in clear flowing water and are sensitive to pollution and oxygen depletion. Caddisflies are found across a range of habitats from cool streams to warm streams, lakes, marshes, and ponds (Peckarsky et al. 1990). Caddisflies found in standing water can tolerate some pollution. Crustacea Scuds (Amphipoda) Freshwater scuds are found in unpolluted lakes, ponds, streams, springs, and subterranean waters (Pennak 1989). They require abundant dissolved oxygen and many species only inhabit cold waters.

Macroinvertebrates dominant in moderately polluted waters

For drawings of moderately tolerant organisms, click here. Slow flow areas are made up of decomposer communities that tolerate lower dissolved oxygen levels and higher organic matter and sedimentation. Riffle-dwelling communities are more sensitive to increasing pollution than communities in the pools or slow flowing areas in the same stream. Insecta Mayflies (Ephemeroptera) Mayflies are most abundant in cool, unpolluted, headwater streams but they may be found in standing (lentic) water as well. They prefer clean water and an average oxygen supply, but some species can tolerate low dissolved-oxygen levels (e.g. Callibaetis spp.) (Peckarsky et al. 1990). Mayfly nymphs tend to be grazers, feeding on algae or detritus (Peckarsky et al. 1990). Caddisfly larvae (Trichoptera) Generally caddisfly larvae are found in clear flowing water and are sensitive to pollution and oxygen depletion. Caddisflies are found across a range of habitats from cool streams to warm streams, lakes, marshes, and ponds (Peckarsky et al. 1990). Caddisflies found in standing water can tolerate some pollution. Caddisfly species are found in every functional feeding group (Peckarsky et al. 1990). Beetle larvae and adults (Coleoptera) Adults are more tolerant of low-oxygen conditions and low pH by living at the land water interface. Larvae are more sensitive, prefering, clean waters but may be found in either flowing or standing waters. There are two major groups of Coleoptera, those whose species are found in ponds or lentic areas of streams (e.g., Dytiscidae, Haliplidae, Hydrophilidae), and those that live only in fast flowing (lotic) streams (e.g., Elmidae, Dryopidae, Psephenidae) (Peckarsky et al. 1990). Dragonfly nymphs and damselfly nymphs (Odonata) Odonata nymphs prefer slow-moving or standing (lentic) water. They are able to withstand low oxygen levels and are thus more tolerant of organic matter enrichment (Hawkes 1985) Odonata are predators (Peckarsky et al. 1990). Cranefly larvae (Diptera Tipulidae) Cranefly larvae are found in moss, silt, and leaves at the bottom of either standing or flowing waters. Water boatman (Hemiptera Notonectidae) Water boatmen are found in shallow slow-moving streams and rivers as well as in ponds and lakes. They are somewhat tolerant of pollution. Flat worms (Turbellaria-Platyhelminthes) Turbellaria are found beneath rocks, logs, or dead leaves in springs, spring brooks, ditches, wetlands, streams, and lakes (Peckarsky et al. 1990). They are sensitive to organic pollution but prefer moderate nutrient levels (De Lange 1994). Some (nontriclads) can tolerate low oxygen levels and can even survive where the water is only 5% oxygen saturated (Peckarsky et al. 1990). Flatworms tend to be found in cold water environments although some species (nontriclads) will be found across all temperatures. Turbellaria may eat other living, as well as dead, invertebrates, detritus or decaying organic matter, and some prefer diatoms (Pennak 1989). Crustacea Crayfish (Decapoda-Astacidea) Crayfish are relatively pollution tolerant and can be found in standing and flowing waters. They may be found in a variety of environments, from streams and lakes to wetlands, including wet meadows which have no open water (Pennak 1989). Crayfish may have ecological requirements particular to their habitat. Stream species tend to be less tolerant of changes in temperature, pH, and dissolved oxygen than lake and pond species. Mollusca Mussels and clams (Bivalvia) Most bivalves can not tolerate high turbidity (De Lange 1994; Pennak 1989). As filter-feeders, sediments and organic matter prevent them from feeding. Although clams are generally tolerant of siltation, sand clams are extremely sensitive to severe siltation (De Lange 1994; Pennak 1989).


Macroinvertebrates dominant in fairly polluted waters.

Turbidity reduces light penetration and submersed aquatic plant productivity. Thus turbidity will affect those macroinvertebrates depending on plant matter for food and predator macroinvertebrates that rely heavily on visual location of prey. Filter feeders' filtering mechanisms may be blocked by sediment. As sedimentation increases, rock dwelling or attaching macroinvertebrates such as mayflies, stoneflies, and caddisflies, will be replaced by silt-tolerant oligochaetes, chironomids, and lunged snails. Insecta Black fly larvae (Diptera Simuliidae) Simuliidae are filter feeders that can filter very fine particles (Peckarsky et al. 1990). Midge larvae (Diptera-Chironomidae) Midges are found in all water types, including salt water. They live in the silt bottom, on solid substrates, or on aquatic plants. Crustacea Sowbugs/pillbugs (Isopoda-Asellidae) Moderately intolerant of pollution, isopods may be found in streams, headwaters, ponds, or shallow areas of lakes (Peckarsky et al. 1990). Isopods feed on dead animal and plant matter thus, they will increase in number under eutrophic conditions (Peckarsky et al. 1990). Mollusca Snails (Gastropoda) Snails with gills are sensitive to oxygen depletion. However, those with lungs (pulmonate snails) can tolerate water with little or no oxygen. Annelida Leeches (Hirudimea) Leeches are generally pollution tolerant, however, some species of leeches are much less pollution tolerant than others (Pennak 1989; Peckarsky et al. 1990). Leeches are found in warm water of shallow standing water (Peckarsky et al. 1990). They generally can not tolerate very acidic waters. They are also limited by low calcium content (Pennak 1989). Siltation does prevent leeches from attaching to stones or other objects. Leeches feed on dead organic matter, snails, insects, oligochaetes, and other small invertebrates (Pennak 1989).

Macroinvertebrates that can be found in severely polluted waters

Extremely polluted waters, receiving high inputs of organic matter or nutrient enrichment from non point and point sources, tend to have a low diversity of macroinvertebrates. Only those species capable of surviving and thriving under low dissolved oxygen or highly turbid conditions inhabit polluted waters. The species that predominate are species such as tubificid oligochaetes and red chironomid dipteran larvae (Peckarsky et al. 1990). Annelida Aquatic worms (Oligochaeta) Tubifex worms (tubificids) are found in soft sediments rich in organic matter. Some aquatic worm species actively seek habitats with organic pollution and low dissolved oxygen levels (Pennak 1989; Peckarsky et al. 1990). Aquatic worms feed on detritus, algae, and diatoms in the substrate (Pennak, 1989). Leeches (Hirudimea) Leeches are generally pollution tolerant, however, some species of leeches are much less pollution tolerant than others (Pennak 1989; Peckarsky et al. 1990). Leeches are found in warm water of shallow standing water (Peckarsky et al. 1990). They generally can not tolerate very acidic waters. They are also limited by low calcium content (Pennak 1989). Siltation does prevent leeches from attaching to stones or other objects. Leeches feed on dead organic matter, snails, insects, oligochaetes, and other small invertebrates (Pennak 1989). Mollusca Snails (Gastropoda) Snails with lungs (pulmonate, e.g. Physa spp.) can tolerate water with little or no oxygen (Pennak 1989).