Sengupta, M. and Dalwani, R. (Editors). 2008.
Proceedings of Taal2007: The 12th World Lake Conference: 95-98
Benthic Invertebrates  A Crucial Tool in Biomonitoring of Lakes
Diya Bhattacherjee
INTRODUCTION Advantages of Using Benthic Macroinvertebrates:
Bioindicators are organisms whose presence, absence 1. They are good indicators of localized
or condition provides information about the conditions of water quality due to their
environmental quality. Every organism has unique limited mobility. As such, they are well
environmental requirements to be healthy and suited for the assessment of site-specific
reproduce successfully. The presence or absence of pollution impacts.
healthy populations of organisms within their 2. They are sensitive to environmental impacts
habitats is a sign of unique environmental from both point and non-point sources of
characteristics. pollution.
Chemical and physical tests give information 3. They integrate the effects of short-term
that is accurate only for that moment when sample is environmental variations, such as oil spills
taken. The presence of a mixed population of healthy and intermittent discharges.
aquatic insects or fish usually indicates that the water 4. Sampling is relatively easy and inexpensive.
quality has been good for some time 5. They are holistic indicators of overall water
quality, even for substances that may be
What are freshwater macro-invertebrates? present, but at lower than detectable levels.
6. They serve as the primary food source for
Benthic invertebrates represent the larger many species of commercially and
organisms that inhabit the bottom substrates (the recreationally important fishes.
benthos) such as sediments, snags and aquatic plants, 7. Unlike chemical monitoring, where impacts
of aquatic habitats for at least part of their life cycle. to the environment tend to be by inference,
As a general guideline benthic invertebrates include not direct determination, they provide a
those species whose body width exceeds 500 um at direct measure of water quality in a manner
some time during its life cycle, or are visible to the consistent with the goals of the Clean Water
naked eye. Typically this fauna includes aquatic Act.
insects (e.g. stoneflies, mayflies, caddisflies, beetles, 8. They can be used to assess nonchemical
true bugs, true flies), crustaceans (e.g. isopods, impacts to the aquatic habitat, such as by
amphipods, crayfishes), molluscs (e.g. snails, clams, thermal pollution, excessive sediment
mussels), annelids (e.g. leeches, oligochaetes), and a loading (siltation), or eutrophication.
few other groups (e.g. proboscis worms, flatworms 9. To the general public, impacts to resident
benthic macroinvertebrate communities are
more tangible measurements of water
quality than more esoteric listings of
chemical test results.
10. When monitored together with relevant
chemical/physical parameters, benthic
macroinvertebrate communities can be used
to identify sources of impairment.
Benthic Macroinvertebrates Usually Indicative of
Good Water Quality
What is the ecological importance of benthic
macroinvertebrates?
Benthos is an important part of the food chain,
especially for fish. Many invertebrates feed on algae
and bacteria, which are on the lower end of the food
chain. Some shred and eat leaves and other organic
matter that enters the water. Because of their
abundance and position as  middlemen in the
aquatic food chain, benthos plays a critical role in the
Mayfly nymphs are often abundant wherever the
natural flow of energy and nutrients. As benthic
water is clean. They are sensitive to various types of
invertebrates die, they decay, leaving behind
water pollution, including low dissolved oxygen,
nutrients that are reused by aquatic plants and other
ammonia, biocides, and metals.
animals in the food chain
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Stonefly nymphs are usually found only in cool,
well-oxygenated waters free of pollution. Though not Midges (chironomids) are among the most common
usually found in the numbers characteristic of of aquatic invertebrates. They occupy a variety of
mayflies, the presence of even a few stoneflies is aquatic habitats, including lakes, ponds, bogs, rivers,
indicative of good water quality. creeks, and marshes. They even exploit manmade
habitats such as sewage treatment plants, water
treatment plants, fish pools, irrigation ditches, and
birdbaths. Many species are very tolerant of
pollution.
Most caddisfly larvae, many of which build portable
cases of stones, sticks, sand and other detritus, are
intolerant of water pollution.
Aquatic sowbugs, or freshwater isopods, are
abundant in waters enriched with organic nutrients
and low in dissolved oxygen. They are commonly
observed in the recovery areas below sewage
treatment plants.
Aquatic beetles are common in well oxygenated,
swiftly running waters; many species are referred to
as "riffle beetles." They are usually indicative of
clean water since they are sensitive to wetting agents
(soaps and detergents) and other pollutants.
Illustrations modified from W.B. Clapham, Jr.,
"NATURAL ECOSYSTEMS," The Macmillan
Company, New York, 1973.
Black fly larvae are filter feeders, capturing and
Benthic Macroinvertebrates Usually Indicative of
ingesting plankton and bacteria from the surrounding
Poor Water Quality
water with specialized antennae. Some species are
very tolerant of poor water quality and thus can be
used as indicators of pollution.
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Diporeia
Diporeia is sensitive to low oxygen concentrations
and to many toxicants (Nalepa and Landrum, 1988),
and due to its high lipid content and absence of
biotransformation capability, has a high
bioaccumulation potential for organic contaminants
(Landrum and Nalepa, 1998). These characteristics
make it an appropriate organism for biomonitoring,
both for its inherent ecological importance, and for
its potential usefulness as an indicator of overall
Leeches and other segmented worms are very
system health
common in our lakes and streams, though not often
noticed. They are tolerant of poor water quality and
severe pollution.
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