Macroinvertebrates (required) Print...

Materials
  • Data Collection Student Worksheet (optional)
  • kick seine or dip net: see how to build a kick seine
  • white plastic sheet (if you plan to observe your specimens at the site)
  • wading boots
  • Shallow pans, such as dish pans, for each group
  • Ladles, scoops, spoons, tweezers, and / or eyedroppers to use in transferring samples to smaller containers
  • Small containers to separate the samples for study (e.g. baby food jars, petri dishes, ice cube trays, etc.)
  • Hand / magnifying lenses
  • Rulers
  • Macroinvertebrate identification keys:
    • free downloadable Bug ID charts: front-page - back-page (in Adobe .pdf format - courtesy of Save Our Streams)
    • Internet access to view the recommended interactive Macroinvertebrate Identification Key (optional - courtesy of Save Our Streams)
    • other macroinvertebrate books or resources (available in the Reference Material section of the project web site)
      •
  • If you plan to transport and identify your specimens back in the classroom:
    • plastic buckets with lids: to carry the specimens
    • microscopes and slides (optional)
    •

Background Information
Macroinvertebrates are organisms that do not have a backbone and are visible without a microscope. In most streams, the energy available to organisms is stored in plants and made available to animal life either in the form of leaves and algae that are eaten by macroinvertebrates. In turn, the macroinvertebrates are a source of energy (food) for larger animals such as fish, which are a source of energy (food) for birds, raccoons, and humans.

In this project, macroinvertebrate sampling is coupled with chemical water quality sampling. The reason for this is quite simple.  The process of identifying stream pollution with water analysis alone is time intensive and can only provide limited information from the time of sampling. Even the presence of fish may not provide information about a pollution problem because fish can move away to avoid polluted water and then return when conditions improve. However, most stream-bottom macroinvertebrates cannot move to avoid pollution. Therefore, a macroinvertebrate sample can serve as an indicator of water quality by providing more information about pollution or the overall water quality that is not present at the time the sample is collected.

Some stream-bottom macroinvertebrates cannot survive in polluted water while others can survive or even thrive in polluted water. For example, species commonly found in colder waters (see temperature) that need high levels of dissolved oxygen include pike, trout, bass, salmon, mayfly larvae, stonefly larvae, and caddisfly larvae are indicators of a healthy stream. Species commonly found in warm waters such as sludge worms, black fly larvae, and leeches are more tolerant of low dissolved oxygen levels, indicators of an unhealthy stream. Additionally, useful stream-bottom macroinvertebrate data are easy to collect without expensive equipment.

Finally, a healthy ecosystem supports diversity of organisms, so in a healthy stream, the stream-bottom community will include a variety of ALL of the pollution-sensitive macroinvertebrates. Conversely, an unhealthy stream will support only a few types of non-sensitive macroinvertebrates.

Test Procedure
Collecting the water sample and identifying the macroinvertebrates can either be done as one activity at the sampling site in which case all of the following test procedures can be followed in the order below OR Part B. Identify the Macroinvertebrates can be completed back in the classroom. If you plan to transport and identify your specimens back in the classroom, you can place the contents of the kick seine (including the debris) into a bucket that is partly filled with stream water. If you put a lid on the bucket (recommended), you should leave some air space above the water in the bucket to allow mixing of oxygen.

  1. Collect the Sample
    The two (2) most common methods to sample macroinvertebrates include the kick seine and the dip net methods. The kick seine is most efficient for sampling streams with rocky or gravel stream beds where the velocity of the water will move the dislodged organisms into the net. The dip net method can be used in a variety of habitats and used like the kick seine or used for scooping through the water.
    1. Choose a Sampling Site and Method
      The first step is to choose a sampling site to ensure that the appropriate equipment is obtained (i.e. kick seine or dip net). Find a riffle that is typical of the stream. A good riffle for sampling will have cobble-sized stones, fast-moving water, and a depth of 10 to 20 centimeters. Select a 1 meter by 1 meter area within the riffle for sampling.
       
    2. Position your Kick Seine / Drop Net
      Position your kick seine / drop net at the downstream end of the sampling area and proceed slowly walking upstream. The net should be stretched out to its full meter width with the bottom edge lying firmly against the stream bed. No water should wash under or over the net. If needed, small rocks can be used to weigh down the bottom edge of the net.
      NOTE: To avoid losing macroinvertebrates, do not stand in or disturb the sampling area before the net is in place.
       
    3. Gather the Specimens in the Net
      One meter at a time, gently move or "kick" the substrate by using the toe or heel of a boot and dislodge the upper layer of the stream bed.  If a larger substrate is encountered, such as a large piece of wood, the object should be picked up and rubber by hand or a small brush to dislodge the attached organisms.
       
    4. Collect the Sample
      Slowly lift the kick seine out of the water with a forward scooping motion. The object is to avoid losing any macroinvertebrate specimens while the seine is lifted. This will be easier if one person holds the top of the kick seine handles while the other person holds the bottom of the handles.
       
    5. Remove the Specimens from the Net
      Carry the kick seine to the stream bank and spread it out flat over a white plastic sheet (this will help you see the macroinvertebrates easier). Carefully examine the net and the collected debris for macroinvertebrates. Look carefully as many specimens will be small and hard to see.
      NOTE: If you plan to transport and identify your specimens back in the classroom, you can place the contents of the kick seine (including the debris) into a bucket that is partly filled with stream water (see above).
       
  2. Identify the Macroinvertebrates: NOTE: this can either be done at the site or back in the classroom.
    The identification of macroinvertebrates can be completed by using some very simple keys created for students. For some specimens, magnification with a hand lens will be needed to see the identification characteristics. Most identification keys involve choosing between pairs of opposite choices or descriptive statements. The students will make observations of the organisms and decide which statement best describes the organism. This is repeated until the macroinvertebrate is identified.

    If students reach a point in the selection of descriptive statements at which neither of the statements apply, they can work their way back through the preceding pairs of statements and perhaps reconsider the choices. In some cases, the additional information about the individual macroinvertebrates will be helpful. In others, they will find that they are unable to identify the particular macroinvertebrate and will have to identify it as "unknown" unless contacting an aquatic biologist or more information to help with the identification.

    Some macroinvertebrates (such as some caddisfly larva) might be found in a protective case of sand, small sticks, or other material. It may be necessary to remove these cases in order to make an identification. 

    1. Separate into Small Groups
      Divide the class into groups of 4 - 6 students.
       
    2. Make a "Gross Examination"
      Before the students take their own samples from the collected pond water, gather them around the large sample for an initial "gross examination." Ask them to share their observations. Tell them that it will be possible to identify most of the organisms in the sample using just a hand lens or the eye.
       
    3. Sort the Specimens into Large Containers (1 per group)
      Using tweezers or fingers, place all the specimens into separate containers so that each group will have one. Each group should then take the larger containers making sure that they dip into the container and don't just collect from the surface. They will then have a large sample from which each student can collect smaller samples for study.
       
    4. Sort the Specimens into Small Containers
      After each group has collected a sample in the dish pan, each student should use an eyedropper or spoon to collect samples from the pans and separate them into smaller containers for closer examination.
      IMPORTANT: Students should NOT return their sample to the original dish pan once they have been identified because the macroinvertebrates in it have already been counted.
       
    5. Identify the Specimens
      Using an identification key (below) or guide, students should observe and identify the type and number of visible organisms found in each sample and record their findings on the optional Data Collection Student Worksheet. Student should make notes about organisms that they cannot identify by writing and making pencil sketches. They should make as many observations as they can including color, size, shape, way of moving, number of legs, etc.
      NOTE: If low powered microscopes are available, use the eyedroppers to place a specimen on a depression (concave) slide.
    6. If possible, students can browse through additional resources and see if they can identify specimens that are not on the list.

What to Expect
The presence or absence of certain organisms, or indicator species, reveals much about the quality of the water. Some macroinvertebrates are extremely sensitive to changes in water quality and are found in large amounts, in waters that are generally clean, or unpolluted by organic wastes and have more oxygen. Other macroinvertebrates are not sensitive to pollution; therefore if a large number of these organisms are found in a sample, it would serve as an indicator of poor water quality.

The Guidelines established by the Save Our Streams Program will be followed for this project. Save Our Streams identifies three (3) groups of macroinvertebrates based on their sensitivity to pollution: pollution sensitive, somewhat pollution tolerant and pollution tolerant. The Save Our Streams method involves collecting a sample of macroinvertebrates from the stream, identifying the organisms and rating the water quality.  Water quality ratings of excellent, good, fair, and poor are based on the pollution tolerance levels of the organisms found and the diversity of organisms in the sample.

A stream with excellent water quality should support organisms
from ALL three (3) pollution tolerance groups.

SENSITIVE to pollution SOMEWHAT pollution tolerant TOLERANT to pollution
  • Mayfly larvae
  • Stonefly larvae
  • Caddisfly larvae
  • Dobsonfly (often called hellgrammite)
  • Riffle Beetle (adult)
  • Water Penny larvae
  • Planaria (also called flatworm)
  • Gilled snail
  • Alderfly larvae
  • Crane fly larvae
  • Fishfly larva
  • Watersnipe fly larvae
  • Damselfly larvae
  • Dragonfly larvae
  • Riffle Beetle larvae
  • Whirligig Beetle larvae
  • Clam or Mussel
  • Crayfish
  • Scuds
  • Sowbug
  • Midge fly larvae
  • Black fly larvae
  • Chironomid larvae
  • Aquatic worms
  • Lung snails
  • Leeches

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[Menu: Introduction - Equipment]
[Required Tests: General Observations - Temperature - pH - Dissolved Oxygen - Macroinvertebrates]
[Optional Tests: Nitrates - Phosphates - Biological Oxygen Demand - Turbidity - Coliform Bacteria]
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