Introduction to Benthic
Macroinvertebrates
Trout In The Classroom
Virginia Council of Trout Unlimited
2009 / 2010
State Water Quality Standards
Standards are based on how we use water:
1.
2.
3.
Standards include a general requirement that
all state waters are free of pollutants harmful to
animal, plant, and aquatic life. This standard
allows the state to consider stream habitat and
aquatic insects as indicators of water quality.
Aquatic Insects as BioIndicators of Water Quality
There are important reasons why
benthic macroinvertebrates are used
to assess water quality:
1) they are found in all streams;
2) there are many different species;
3) they stay in the same spot in a stream;
4) they react to different conditions in the stream
over long periods of time; and
5) they are easy to sample and identify.
Benthic Macroinvertebrates
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•
•
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Benthic = dwelling on stream bottom
Macro = large enough to see with naked eye
Invertebrates = without a backbone
Other benthic aquatic organisms = aquatic
insects that have three body parts (head, thorax,
abdominal segment) and six legs
When you try to identify an organism, these
are some details to notice
Key ID Features -Legs
Six true legs plus
lateral filaments
Six
segmented
legs
More than six
legs
prolegs
Key ID Feature – Tails
Tail-like
projection
Featherlike tails
Two tails
No tail or
tiny tail
Details to notice: gills
Abdominal
gills
Abdominal
filamentous
gills
Internal gills
Practice ID
Wing pads
• Body shape?
• Head? Size relative to
body?
• Legs? Number? Length?
Placement?
• Details? Antennae?
Eyes? Wings? Tail?
Specimen #1
Specimen #2
Specimen #3
Specimen #4
Specimen #5
Specimen #6
Specimen #7
Specimen #8
Specimen #9
Specimen #10
Specimen #11
Specimen #12
Specimen #13
Specimen #14
Specimen #15
Benthic Macroinvertebrates
can be classified according to
their sensitivity to pollutants.
Sensitive
Mayfly larvae
Stone Fly larvae
Most caddisfly larvae
Beetles (adults and larvae)
Somewhat sensitive
Dragonfly and damselfly larvae
Netspinner caddisfly larvae
Crayfish
Gilled snails
Aquatic sowbugs
Scuds
Clams and mussels
True fly larvae
Hellgrammites, Fishfly and Alderfly
larvae
Tolerant
Lunged snails
Black fly larvae
Midge larvae
Aquatic worms
Flatworms
Leeches
Interpreting Benthic Data
Benthic macroinvertebrates can be
classified according to their
sensitivity and tolerance to water
pollution.
Identify and Tally
Individual Species Metric
Tolerance Metric
Compute Mulitmetric Index
Rate the Stream
Credits
Slides and notes used in this presentation were
provided for educational purposes by:
• Virginia Save Our Streams
• Virginia Department of Conservation and
Recreation
• Alice Furguson Foundation – Bridging the
Watershed
• Audubon Naturalist Society
And a very special thanks to Darrell Schwalm of
the Shenandoah Valley TU chapter for putting this
presentation together.