Macroinvertebrate M&Ms

Purpose: To learn to describe and identify the quality of a stream site by analyzing its macroinvertebrates using a model.

Summary: Students will learn about water quality indicators using candy to represent a macroinvertebrate sample. Sorting the candy and evaluating what is found will tell students about the quality of the water. This exercise can be used prior to field macroinvertebrate sampling to reinforce concepts.

Background: Itís not always easy to tell if a stream is in trouble. If you see strange colors or dead fish or other wildlife, you might assume the water quality is poor. However, we need to know if water quality is degrading long before such extreme consequences are seen. For this reason, biologists often choose to use macroinvertebrate analyses to monitor water quality. These organisms (commonly called ìbugsî) generally remain within a small range of the stream during their lifetime, and are quick to respond to changes in water aulity.

To determine relative health of a stream, biologists look at the types of macroinvertebrates that live in different reaches. Different species have different tolerance levels to pollution. If many pollution-intolerant species, such as stonefly or caddisfly nymphs, are present, then the water quality is probably quite good. Although the presence of certain species indicates good water quality, the absence of these species does not necessarily indicate bad water quality. Other factors besides pollution may have accounted for their absence. For this reason, scientists generally rely upon a variety of methods for assessing water quality, including water chemistry and stream functioning condition assessments. However, since macroinvertebrates are easy to collect and relatively easy to identify, they can provide a relatively low cost method for assessing trends in water quality.

Sensitive or intolerant species are easily killed, impaired, or driven off by bad water quality. These include:

Stonefly nymph

Dobsonfly nymph

Mayfly nymph

Caddisfly larva

Water penny

Somewhat tolerant species will survive under a variety of conditions, and may be found in both good and bad quality water.
Sowbug

Scuds
Beetle larva

Cranefly larva
Crayfish
Alderfly larva
Dragonfly nymph

Clam

Tolerant species are capable of surviving poor water quality.

Leeches

Aquatic worms
Midge larva

Lunged snail

Materials:

1. M&Ms or Skittles (allow for consumption!)
2. Small plastic bags, one bag per group of students
3. Graph paper
4. Colored pencils

Procedure:

1. Divide the candy randomly into the bags. You may have either one bag per student, or one bag per group of students. There should be about 30 pieces of candy per bag. Each bag represents all the macroinvertebrates collected at a sample site.
2. Have the class assign a macroinvertebrate to each color of candy. For example, red might represent a stonefly nymph, yellow a cranefly larva, green a leech, etc. See example below.

Example:

Color (M&Ms) Macroinvertebrate

Red Stonefly (intolerant)

Orange Caddisfly larva (intolerant)

Yellow Beetles (somewhat tolerant)

Green Cranefly larva (somewhat tolerant)

Blue Midge larva (tolerant)

Dark brown Leeches (tolerant)

3. Distribute a student worksheet and graph paper to each student or group. Have the students create a bar graph for the macroinvertebrates in the sample. Label the x-axis with the names of the macroinvertebrates represented by candy, and the y-axis with the number of individuals in the sample.
4. Give each student or each group a bag of candy. Tell the students to separate and count the number of pieces in each color group, enter the results on the data sheet, and graph the results using the colored pencils or crayons.
5. Using the Beginner's Key to Macroinvertebrate Groups, have students try to determine the water quality based on their sample.

Beginner's Key to Macroinvertebrate Groups

(use handout from Discover Wetlands)

GROUP 1: These organisms are not tolerant of pollution. If your sample consists mostly of these organisms, the water quality is generally good to excellent.

• Stonefly
• Caddisfly
• Water penny
• Riffle beetle
• Mayfly
• Gilled snail

• Dobsonfly

GROUP 2: These organisms will be found in a wide variety of water quality conditions. They are tolerant of some level of pollution.

• Crayfish
• Sowbug
• Scud
• Alderfly larva
• Fishfly larva
• Damselfly
• Watersnipe fly larva
• Cranefly
• Beetle larva
• Dragonfly
• Clam

GROUP 3: These organisms are more tolerant of pollution, and when found to be the largest segment of the population, generally indicate fair to poor water quality.

• Aquatic worms
• Midge fly larva
• Blackfly larva
• Leech
• Pouch snail and pond snails
• Other snails

(Need to add pix of each group)

Macroinvertebrate M&Ms Student Worksheet

Color	Macroinvertebrate	Number counted
Red
Orange
Yellow
Green
Blue
Dark Brown

1. Do you think the water quality at your sample location is excellent, good, fair or poor?

2. Why are the samples different?

3. What might that suggest about the stream water quality and the sampling locations?

4. What pollutants might be responsible?

Resources

Aquatic Macroinvertebrate Identification Key, web-based interactive key, http://www.people.virginia.edu/~sos-iwla/Stream-Study/Key/Key1.HTML

A Community Water Quality Monitoring Manual for Waterwatch Victoria, web resource, www.vic.waterwatch.org.au/fortheteacher/manual/index.htm (see section on macroinvertebrates under ìBiological Surveysî

Field Guide to Aquatic Macroinvertebrates, 2003, Izaak Walton League, www.iwla.org

Fore, L. S. and A. Wildrick. 1998. Guide to Freshwater Invertebrates. http://www.seanet.com/~leska/Online/Guide.html

Lippy, K., Friesem, J., Vanderburg, S., Usher, L., and Lynn, B, 1995, Discover Wetlands, A Curriculum Guide. Washington State Department of Ecology, Publication #88-16-a, http://www.ecy.wa.gov/pubs/8816a.pdf

Macroinvertebrate Key, web resource, www.people.virginia.edu/~sos-iwla/Stream-Study/Key/MacroKeyIntro.HTML

Monitorís Guide to Aquatic Macroinvertebrates, 1992, Loren Larkin Kellog, The Izaak Walton League of America, www.iwla.org

Rivers Curriculum Guide, Biology, 1998, R. Williams (lead author and project director), Dale Seymour Publications, White Plains, NY.

Streamkeeperís Field Guide, 1996, Tom Murdoch and Martha Cheo with Kate OíLaughlin, Adopt-a-Stream Foundation, www.streamkeeper.org

Vocabulary Words

Abdomen	The rear body section of some invertebrates.
Collectors	Animals that feed on dead or decaying organic matter.
Head	The front body section of invertebrates.
Larvae
Macroinvertebrate	Animals that have no backbone and are visible without magnification.
Metamorphosis	A change in body form during growth and development.
Nymph
Predators	An organism that captures and feeds on other organisms.
Scrapers	Animals that remove and eat green plants and algae off the rocks they are growing on, and graze on surface plants.
Shredders	Animals that chew up pieces of dead plants (leaves, grasses, algae, etc.) and reduce the dead material to very fine pieces that are then excreted.
Thorax	The middle body section of some invertebrates.

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