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Macroinvertebrates and Rapid Biological Assessments Protocols

Rapid Bioassessment Protocols For Use in Streams and Rivers: Periphyton, Benthic, Macroinvertebrates, and Fish, 2nd Edition

Macroinvertebrates can be seen with the naked eye and these are organisms that lack a backbone. In freshwater rivers and streams, they are typically dominated by larval insects. The community as a whole includes snails, insects, crayfish, worms, and many other related organisms. Because these organisms are near the base of the food chain, they tend to have a limited ability to relocate, and they tend to be very vulnerable to short-term and long-term changes in water quality; they can be used as indicators of in-stream quality and changes in water quality with time. Because of the many thousands of species and because of the complexity of the taxonomic system, we are providing general information on using macroinvertebrates to evaluate and benchmark in-stream water quality.

Table 1 | Definitions of best candidate benthic metrics and predicted direction of metric response to increasing perturbation

Category Metric Definition Predicted population response to increasing perturbation
Richness measures Total Number of taxa Measures of the overall variety of the macroinvertebrate assemblage Decrease
Number of EPT taxa Number of taxa in the insect orders Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies) Decrease
Number of Ephemeroptera Taxa Number of mayfly taxa (usually genus or species level) Decrease
Number of Plecoptera Taxa Number of stonefly taxa (usually genus of species level) Decrease
Number of Trichoptera Taxa Number of caddisfly taxa (usually genus or species level) Decrease
Composition measures % EPT Percent of the composite of mayfly, stonefly, and caddisfly larvae Decrease
% Ephemeroptera Percent of mayfly nymphs Decrease
Tolerance/Intolerance measures Number of Intolerant Taxa Taxa richness of those organisms considered to be sensitive to perturbation Decrease
% Tolerant Organisms Percent of macrobenthos considered to be tolerant of various types of perturbation Increase
% Dominant Taxon Measures the dominance of the single most abundant taxon. Can be calculated as dominant 2, 3, 4, or 5 taxa. Increase
Feeding measures % Filterers Percent of the macrobenthos that filter FPOM (fine particulate organic matter) from either the water column or sediment Variable
% Grazers and Scrapers Percent of the macrobenthos that scrape or graze upon periphyton Decrease
Habit measures Number of Clinger Taxa Number of taxa of insects Decrease
% Clingers Percent of insects having fixed retreats or adaptations for attachment to surfaces in flowing water. Decrease


Composition measures can be characterized by several classes of information, i.e., the identity, key taxa, and relative abundance. Identity is the knowledge of individual taxa, associated ecological patterns, and environmental requirements (Barbour et al. 1995). Key taxa (i.e., those that are of special interest or ecologically important) provide information that is important to the condition of the targeted assemblage. The presence of exotic or nuisance species may be an important aspect of biotic interactions that relate to both identity and sensitivity. Measures of composition (or relative abundance) provide information on the make-up of the assemblage and the relative contribution of the populations to the total fauna (Table 2). Relative, rather than absolute, abundance is used because the relative contribution of individuals to the total fauna (a reflection of interactive principles) is more informative than abundance data on populations without a knowledge of the interaction among taxa (Plafkin et al. 1989, Barbour et al. 1995).

The premise is that a healthy and stable assemblage will be relatively consistent in its proportional representation, though individual abundances may vary in magnitude. Percentage of the dominant taxon is a simple measure of redundancy Plafkin et al. 1989). A high level of redundancy is equated with the dominance of a pollution-tolerant organism and a lowered diversity. Several diversity indices, which are measures of information content and incorporate both richness and evenness in their formulas, may function as viable metrics in some cases, but are usually redundant with taxa richness and % dominance (Barbour et al. 1996b).

Table 2 | Definitions of additional potential benthic metrics and predicted direction of metric response to increasing perturbation.

Category Metric Definition Predicted response to increasing perturbation References
Richness measures Number of Pteronarcys species The presence or absence of a long-lived stonefly genus (2-3 year life cycle) Decrease Fore et al. 1996
Number of Diptera taxa Number of "true" fly taxa, which includes midges Decrease DeShon 1995
Number of Chironomidae taxa Number of taxa of chironomid (midge) larvae Decrease Hayslip 1993, Barbour et al. 1996b
Composition measures % Plecoptera Percent of stonefly nymphs Decrease Barbour et al. 1994
% Trichoptera Percent of caddisfly larvae Decrease DeShon 1995
% Diptera Percent of all "true" fly larvae Increase Barbour et al. 1996b
% Chironomidae Percent of midge larvae Increase Barbour et al. 1994
% Tribe Tanytarsini Percent of Tanytarisinid midges to total fauna Decrease DeShon 1995
% Other Diptera and noninsects Composite of those organisms generally considered to be tolerant to a wide range of environmental conditions Increase DeShon 1995
% Corbicula Percent of Asiatic clam in the benthic (bottom) assemblage Increase Kerans and Karr 1994
% Oligochaeta Percent of aquatic worms Variable Kerans and Karr 1994
Tolerance/Intolerance measures Number of Intolerant Snail and Mussel species Number of species of molluscs generally thought to be pollution intolerant Decrease Kerans and Karr 1994
% Sediment Tolerant organisms Percent of infaunal macrobenthos tolerant of perturbation Increase Fore et al. 1996
Hilsenhoff Biotic Index Uses tolerance values to weight abundance in an estimate of overall pollution. Originally designed to evaluate organic pollution Increase Barbour et al. 1992, Hayslip 1993, Kerans and Karr 1994
Florida Index Weighted sum of intolerant taxa, which are classed as 1 (least tolerant) or 2 (intolerant). Florida Index = 2 X Class 1 taxa + Class 2 taxa Decrease Barbour et al. 1996b
% Hydropsychidae to Trichoptera Relative abundance of pollution tolerant caddisflies (metric could also be regarded as a composition measure) Increase Barbour et al. 1992, Hayslip 1993
Feeding measures % Omnivores and Scavengers Percent of generalists in feeding strategies Increase Kerans and Karr 1994
% Ind. Gatherers and Filterers Percent of collector feeders of CPOM (coarse particulate organic matter) and FPOM (fine particulate organic matter) Variable Kerans and Karr 1994
% Gatherers Percent of the macrobenthos that "gather" Variable Barbour et al. 1996b
% Predators Percent of the predator functional feeding group. Can be made restrictive to exclude omnivores Variable Kerans and Karr 1994
% Shredders Percent of the macrobenthos that "shreds" leaf litter Decrease Barbour et al. 1992, Hayslip 1993
Life cycle measures % Multivoltine Percent of organisms having short (several per year) life cycle Increase Barbour et al. 1994
% Univoltine Percent of organisms relatively long-lived (life cycles of 1 or more years) Decrease Barbour et al. 1994


Related Links

Surface Water Water Quality Guidelines

Macroinvertebrate Field Guide - Biological Indicator Organisms - Kentucky Water Watch

This site has the organisms arranged by their sensitivity to pollution, i.e.,

Group One Taxa - Pollution Sensitive Organisms  (caddisfly larvae, dobson fly, may fly, water penny, riffle beetle, stonefly nymphs and, snails)

Group Two Taxa - Pollution Intermediate Organisms (beetle larvae, Damselfly Nymphs (Order Odonata), Dragonfly Nymphs (Order Odonata), Scuds (Order Amphipoda), Crayfish (Order Decapoda), Sowbugs (Order Isopoda), Clams (Class Bivalvia (aka Pelecypoda)), and Crane Fly Larvae (Family Tipulidae))

Group Three Taxa - Pollution-Tolerant Organisms (Aquatic Worms (Phylum Annelida and others), Pouch Snails (Class Gastropoda), Black Fly Larvae (Family Simuliidae), Leeches (Class Hirudinea), and Midge Larvae (Family Chironomidae))

On-line Macroinvertebrates Key

Macro-invertebrate Data for the Susquehanna River Basin  (Dates range from 1990 to 2017)

Additional Resources

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