Science Junction

Water What-ifs
Macroinvertebrate Surveys Mini-workshop

Introduction

M acroinvertebrates are invertebrates which can be seen without the aid of a hand lens or microscope and are often used as one of the primary indicators of water quality. Some macroinvertebrates, such as stoneflies, mayflies and water pennies, require a high level of dissolved oxygen and their abundance is an indication of good water quality.

Other macroinvertebrates can survive at a lower dissolved oxygen level because they can come to the surface to get oxygen through a breathing or "snorkel" tube or carry a bubble of air with them around their bodies or under their wings. Several species of macroinvertebrates are indicative of water systems with lower dissolved oxygen levels and include aquatic worms and leeches. Lower dissolved oxygen levels are often associated with polluted waters while higher levels indicate good quality water.

There are several reasons why macroinvertebrates are used as water quality indicators:

  1. They are sensitive to changes in the ecosystem.
  2. Many live in an aquatic ecosystem for over a year.
  3. They cannot escape changes in the water quality.
  4. They can be collected very easily from most aquatic systems with inexpensive or homemade equipment.

The life cycle of a macroinvertebrate goes from egg to adult form and they can undergo either complete or incomplete metamorphosis. Complete metamorphosis has 4 stages: egg, larvae, pupa and adult. Organisms which undergo complete metamorphosis include true flies, beetles and caddisflies. Many of these organisms are aquatic for the egg and larval stages, but not in the adult stage.

Incomplete metamorphosis has 3 stages: egg, nymph and adult. Organisms which undergo incomplete metamorphosis include stoneflies, mayflies, dragonflies and true bugs. Many of these organisms, such as dragonflies, do not live in an aquatic ecosystem as adults. Other species such as true bugs, which include the backswimmers, water scorpions and the water striders, are examples of macroinvertebrates which spend their entire lives in the water.

The length of the life cycle of a macroinvertebrate can vary from less than 2 weeks for some midges and mosquitos and two years or longer for some stoneflies, dragonflies and dobsonflies.

 
Goals and Objectives

Macroinvertebrate Surveys Objectives

A fter completing the tutorial you should be able to

  • explain how the interpretation of a macroinvertebrate survey is related to water quality.
  • interpret a macroinvertebrate survey and determine the water quality of the aquatic ecosystem.

Learn the skills

Macroinvertebrate Survey

A macroinvertebrate survey can be accomplished using many different types of equipment and methods. D-frame nets may be purchased if money is available, but a large aquarium net or a bucket is sufficient to accomplish the collection of a sample.

Waders may be used if the sample is taken away from the shore line. Plastic gloves should be worn while sampling and hands should be washed well with antibacterial soap after the collection is complete.

If you are working in a body of water with a swift moving current, collect your sample downstream. Place the bucket or net down into the water and rake along the bottom. Make sure some of the debris on the bottom is disturbed and collected.

Remove the collected sample to shallow pans and begin the identification process.

Click here for identification charts which will help you to accomplish this objective.


For review, click here

Check yourself

If the primary macroinvertebrate in a body of water is a leech, would you rate the water quality as excellent or poor?

Describe the stages of complete metamorphosis. How is this different from incomplete metamorphosis?

 
Post-test

Workshop Wrap-up

Once you have completed the mini-workshops, test your knowledge with the Water Quality Post-test. Once your completed post-test is submitted, you will receive a password which will give you and your students complete access to all areas of the Water What-ifs web site. Thanks for taking part in this research project on water quality.

 
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Last Modified: 8/15/01

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