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Studying Macro-invertebrates
Objective: To compare and contrast macro-invertebrates and learn about their living environments by
means of sampling instruments and classification guides. Through this process, participants will discover
the connections between a river’s water quality and the macroinvertebrates that inhabit the river.
Abstract: An invertebrate is an animal without a spinal column or internal skeleton. The word “macro”
means visible to the naked eye. Examples of macro-invertebrates include: insects, worms, snails, shrimp
and crayfish.
Macro-invertebrates can undergo either incomplete or complete metamorphosis, changing from egg to
adult forms. Some species of macro-invertebrates spend part or all of their life cycle in riverbeds.
Dragonflies, for example, inhabit aquatic ecosystems in the larval stages but not as adults, while water
striders spend their entire lives in the water. These are called “benthic” macro-invertebrates because
they spend at least a portion of their life cycles on riverbeds.
Macro-invertebrates are very sensitive to the physical and chemical changes that occur in water. Each
species of macro-invertebrate also has its own preferred conditions, i.e. they have different needs and
are therefore more or less sensitive to changes in their habitat. Therefore, chemical or physical changes
in a river can result in negative changes in the diversity and size of the populations that inhabit the area.
For example, an increase in pollution can lead to a population reduction in less tolerant species, thus
limiting the ecosystem to organisms that can tolerate the new conditions. Like any organism, macro-
invertebrates are an essential component in the food chain. Imbalances in the population caused by the
elimination of certain species can result in less competition for food. These factors create an unstable
ecosystem which can affect organisms that are further up the food chain.
Macro-invertebrates are abundant and relatively easy to capture. They can also be preserved for later
identification. By observing the diversity and the amount of macro-invertebrates, you can assess the
quality of a body of water and its surrounding environment.
Number of Participants: 4 - 10
Total Hours of Planning Time: 2 Hours
Total Hours for Participants: 5 Hours
Appropriate age of Participants: 10+ years
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Materials:
- Clipboards
- Chart to record data
- Nets (D-nets or kick nets)
- Bucket
- Gloves
- Plastic trays and ice cube trays
- Small bottles (to hold macro-invertebrates)
- Tweezers and pipettes (to handle macro-invertebrates)
- Magnifying glasses
- Microscope
- Visual identification key corresponding to the ecosystem under study (provided in links below)
When sampling at a rocky riverbed, use a kick-net and a D-net. For muddy riverbeds, use a D-net.
Kick net: 1-metre-square net with 0.5 mm (500 microns) mesh held between two wooden uprights
D-net: pocket-shaped fishing net attached to a hoop (approximately 30 cm with 0.5 mm mesh) fixed to a
long handle
Action Plan:
1) Before you begin to collect and classify the macro-invertebrates, be sure to educate your group about
them as well as other insects. Familiarize yourselves with the body parts that are essential for
identification as well as the materials that will be used in the activity.
2) Next, you must determine what type of riverbed you will be working on. There are two methods for
taking a benthic macro-invertebrate inventory: one for rocky riverbeds and one for muddy riverbeds.
Rocky Riverbed Method:
a) Observe the river from the shore to determine which spots are the best for sampling. Be sure to
select an area with a swift current and a bottom that is made up of stones that are 5-25 cm in diameter.
b) Wade into the river (downstream from where you plan to collect, so as to not disrupt the sample
area) and choose a spot to set up your net. Make sure the spot is covered with stones on the bottom
and is at least the width of the net that you are using.
c) Using a kick net: There should be four participants. Two team members hold the net, and two team
members wait, ready to dislodge the macro-invertebrates from the net.
- The net should be steady with the ends of the poles placed into the riverbed. It should be held
on a slight angle, facing downstream.
- Ensure that the net is not completely taut across, as small pockets in the net are needed to
capture the macro-invertebrates.
- Have team members lift rocks and brush them off, dislodging any organisms that are on the
rock’s surface.
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- After a few minutes, have two team members carry the net back to shore to transfer the
collection. Return the net back into the river if you have not collected a sufficient amount.
d) Using a D-net: There should be three participants. One team member holds the net, and two team
members are beside the net, ready to dislodge the macro-invertebrates from the net.
- Place the net firmly on the bottom of the riverbed and face the net towards the current.
- After about 30 seconds, bring the net back to shore to empty it. Return to the river as many
times as needed to collect a sufficient amount of macro-invertebrates for your group to study.
e) To dislodge organisms, have team members lift rocks and clean the surface using a brush. After all of
the rocks have been dislodged, participants should dig their hands into the riverbed to dislodge any
organisms living there.
Muddy Riverbed Method:
a) From the shore, figure out what types of habitats are present at your site and which are most
abundant. Marshy shorelines are typically the most productive habitat in a river, followed by snags
(submerged wood in the water), aquatic plants, mud, sand and gravel.
b) Enter the water and move upstream towards the habitat you will be sampling from. Be sure not to
dislodge any of the rocks you will be using on your way to the site.
c) There should be three group members in the river: one holding the net, one dislodging the macro-
invertebrates, and one standing a distance away holding the bucket.
d) There are different procedures for each type of habitat you encounter:
- Marshy shoreline or aquatic plants: Slide the edge of the net over the stems of aquatic plants.
Scrape in an upward motion.
- Snags: One person scrapes the edge of the trunk while a second person holds the net below to
catch the organisms as they fall.
- Mud, sand and gravel: Scrape across the bottom of the riverbed using the edge of the net,
scraping about 5 cm into the surface.
3) Transfer the macro-invertebrates from the net into a tub or tray. If you are using a kick net, splash
water at the net from behind to dislodge the organisms that are caught in the mesh.
4) Next, have your group sort the macro-invertebrates. Have members group the organisms they believe
are similar together. Magnifying glasses may be used to determine the absence or presence of certain
body parts or features.
5) Using the resources below, try to identify which major groups each of the macro-invertebrates belong
to based on distinctive traits. Label the different trays with the names of the groups you have identified.
Place the organisms you are unable to identify in one group.
6) Count the number of organisms in each group.
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Abundant = More than 20 per group
Common = 5-19 per group
Rare = 1-4 per group
7) To help determine the water quality, use the following information that shows the pollution
sensitivity of specific macro-invertebrates:
Tolerance level of 0-3 = sensitive to pollution
Tolerance level of 4-6 = moderately sensitive to pollution
Tolerance Level of 7-10 = tolerant to pollution
Macro-invertebrate order Tolerance level
Plecoptera (Stone Fly) 1
Ephemeroptera (May Fly) 2
Trichoptera (Caddisflies) 3
Hydropsychidae (Caddisflies) 4
Diptera (mosquitoes, black flies, fruit flies, blow flies, midges and house flies) 5
Tipulidae (Crane Flies) 3
Chironomidae (Midges) 8
Odonate (Dragonfly) 5
Odonate (Damselfly) 5
Megaloptera (fish fly) 0
Megaloptera (alder fly) 4
Coleoptera (water beetles) 4
Hemiptera (backswimmers, waterscorpions and water boatmen) -
Lepidoptera (Butterflies and Moths) -
Bivalvia (two shelled molluscs, bivalves) 8
Gasteropoda (snail, limpet) 7
Decapoda (cray fish) 6
Amphipoda (side-swimmer) 7
Isopoda (isopod) 8
Nematode (round worm) 5
Platyhelminthe (flat worm, planarian) 4
Annelids (leeches) 10
Annélide (aquatic earthworm) 8
Tardigrade(Water Bears) -
Nemerta (Ribbon Worms) 6
Hydracarina (Water Mites) 4
Compare the macro-invertebrates you have collected to this chart to help determine the water quality.
(For example, if many of the organisms you found are sensitive to pollution, the water quality is likely
very high).
8) Share your experience by uploading your project report onto the online Project Database at:
http://www.janegoodall.ca/members-project-registry.php
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Resources to get you started
Benthic Macroinvertebrates
http://www.epa.gov/bioindicators/html/benthosclean.html
Macroinvertebrates as Indicators
http://www.epa.gov/bioindicators/html/invertebrate.html
Water Quality and Aquatic Macroinvertebrates
http://www.ncsu.edu/sciencejunction/depot/experiments/water/lessons/macro/
Guide to Equipment used in Biological Water Sampling
http://www.alanaecology.com/acatalog/Guide_to_Equipment_in_Biological_Water_Sampling.html
Macroinvertebrate Identification
http://sftrc.cas.psu.edu/LessonPlans/Water/PDFs/MacroinvertebratesA.pdf
The Jane Goodall Institute is not responsible for the content of external websites.
Contact:
For more information about this project, contact: sophie@janegoodall.ca
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