Crayfish Corner

Standards: 4.1 Watersheds and Wetlands, 4.3 Environmental Health, 4.7 Threatened, Endangered, and Extinct Species

Duration: 30 to 45 minutes

Setting: Stream, Wetland

Vocabulary: invertebrate, macroinvertebrate, life cycle, wetland, detritus

Summary: Students will search along the edges of streams/wetlands for macroinvertebrates, which will tell students about the health of the stream.

Objectives: Students will gain a deeper understanding of why wetlands and streams are important habitats, and will understand that many small animals live in these areas. These animals need certain things to live, and therefore if you find that animal you know a stream must have those qualities.

Materials: collection trays (anything white in color), white ice cube trays (for separating), plastic spoons or paint brushes (to move invertebrates around), hand nets, invertebrate I.D. cards

Background:

Wetlands and streams are two very important types of habitats. They both give food, water, and shelter to a variety of plants and animals. Some animals just stop by these areas for water or shelter, like a deer coming to a stream to drink, or a migrating bird staying overnight in a wetland as if flies across the world. There are other animals that live in the water. This includes fish, amphibians, and other creatures called “macroinvertebrates. “

The “macro” part of the name means “large” (as opposed to micro which means small), and the “invertebrate” part means something without a spine. A lobster, for example, is a macroinvertebrate because we can see it without a microscope and it has a hard outer shell instead of a skeleton.

Wetlands are very important because they control flooding.  During heavy rains, large amounts of soil get washed into streams. If there are wetlands nearby, though, the wetland can slow down the water and the soil starts to fall out. There are often a lot of nutrients in the soil, though, like pieces of leaves and plant material. Streams that are lined with trees and other plants also get a lot of these nutrients as leaves fall into the stream. The water is moving faster in a stream, though, so it is not as rich as a wetland.

All of the nutrients and plant material that falls in the water become food. Bacteria and fungus arrive first and start to break down the plant material. These little pieces can travel further in the water, and are called “detritus.” After the bacteria, macroinvertebrates come along to eat the dead plant material. These animals, like mayflies, caddis flies, black flies, etc. usually live in the water for only part of their life cycle. Then animals like crayfish, dragonflies, fish, and amphibians (salamanders and frogs) come along to eat the smaller animals. Next, birds, snakes, and mammals like raccoons and otters come along to eat the crayfish, fish, and amphibians. Pretty soon, you have a whole food chain that all started with the plants and nutrients washed into streams and wetlands.

Looking for macroinvertebrates is a good way to tell if streams are healthy. Scientists do this all the time! They go to an area and start to look for all of the macroinvertebrates they can find. The types they find tell them about the stream or wetland habitat. For example, certain macroinvertebrates can only live in areas with lots of oxygen. If you find one of these, you know you are standing in a pretty healthy habitat!

Procedure:

Warm Up:

Ask students to close their eyes and imagine a stream. Now imagine the rocks and plant litter in the water near the edge of the stream. Finally, imagine what is living under those rocks! What do they think calls that habitat home?

Explain the basic properties of the food chain to students if they are unfamiliar with it.

Activity:

Explain to students that they will be interacting with the base of the food chain and doing a collection of the organisms that eat plant matter in the stream, and the ones that eat those. Explain that they want to determine how healthy of an environment the stream or wetland is to live. Therefore, they are going to look for certain “indicator species”—animals that have to live with very specific things (if you find one you know you have a certain quality)—just like scientists do.

Have students take turns collecting water and using nets along the edge of the stream from the bank (or ankle deep in the stream if you allow it) while other students sort and identify the creatures. The most life is found right by the edge of the stream, so students do not need to go far to find them!  Students on the bank can use plastic spoons to scoop up and divide animals, or they can use paintbrushes to gently push them around.

Help students identify the macroinvertebrates they have found. Ask students what they might tell you about the stream. Keep an eye out specifically for the caddis fly larva. The caddis fly is interesting because it is a little like a hermit crab, in that it carries its home around on its back. The difference, though, is that the caddis fly builds its own “shell” by gluing together tiny stones or bits of stick. You can usually find them stuck to the bottom of rocks. Similar to butterflies, caddis fly larvas go through metamorphosis. They hatch from eggs in the water and live there as larva. Eventually, they crawl up a plant growing out of the water and turn into an adult caddis fly. Caddis fly larvas need very oxygenated water to survive, so if you find one you know you have a healthy stream habitat!

Assessment:

Ask students to explain the food chain, and give an example. Ask students how scientists can determine whether or not a stream is healthy.

Enrichment:

Give students scenarios where they find certain macroinvertebrates in a stream and have them determine whether or not it is a good habitat.

Have students draw pictures of the different macroinvertebrates.

Have students each choose a different macroinvertebrate and do a small research paper on it using the Internet.

Pictures/Handouts