Changing With the Tide

In this lesson, students will learn about and act out the functions of the salt marsh habitat. They will learn about the changing nature of salt marshes, and will imitate the actions of the plants and animals that live there in order to understand life in the salt marsh.

Students will:

• describe three different aspects or life forms of the salt marsh;
• compare and contrast the low and high marsh;
• explain what happens in different areas of the marsh at low and high tide; and
• explain the roles different organisms (or other elements) play in the salt marsh by acting out a salt marsh scene.

• Asking Geographic Questions
• Acquiring Geographic Information
• Answering Geographic Questions

Opening:

A salt marsh is a grassy area near the coastline that is greatly affected by the tides. Plants and animals of salt marshes live in different parts of the marsh depending on how tolerant they are to salt, changes in salt concentrations, changes in temperature, and changes in water level. Those with more tolerance to alternately being completely flooded or left "high and dry" at various times, live closer to the ocean. This area closer to the ocean is called low marsh. Those with less tolerance live further inland. They live in what is called the high marsh. The high marsh is flooded only a few hours each day or even just a few hours twice a month. See the descriptions below to find out some interesting adaptations of the different plants and animals that live in the low and high salt marsh.

Tell students that, as a class, they will have the opportunity to act out what happens in a salt marsh. Before they begin this "play," however, they need to understand a few things about salt marshes. Ask them why they think that salt marshes are so salty. (They are near the ocean.) Ask them what they think this means about the water in a salt marsh (other than its being salty). Does it stay the same all the time?

Ask students to briefly look at these Web sites about salt marshes to learn some basic information:

Duck Cove Salt Marsh Project

Dynamics of the Salt Marsh

Canadian Geographic For Kids—CG Kids!

National Geographic Geoaction!—Habitats

Make sure they understand that one of the most important effects the ocean has on salt marshes is the movement of the tides. Ask them the questions below. Write their answers on a chalk or dry-erase board and talk about each one.

• What happens at high tide? (Much of the marsh is under water.)
• What happens to the temperature at high tide on a hot day? (It decreases.) On a cold day? (It is a little warmer.)
• Would a salt marsh be saltier at high tide or at low tide? (High tide, because the ocean is salty, and the creeks that feed the marsh pour in fresh water at low tide.)
• What are three things that plants and animals have to deal with as the tides change? (Changes in water level, changes in temperature, and changes in salinity.)

Detritus—4 copies
A mix of dead plant matter, soil, and small organisms, detritus is washed into the salt marsh by tidal creeks. It is very important to the ecosystem because it feeds nutrients to the plants and important bacteria and other microorganisms that live in the marsh. Many animals feed off of detritus or the organisms that eat it.

Spartina (Pickleweed)—3 copies
Absorbs water through its roots without absorbing much salt. Salt that is absorbed is secreted through its leaves. Its long leaves also get rid of excess heat. Mud in the salt marsh has little oxygen in it, but air tubes connect the surface of the spartina leaves with the roots and bring air down to them. Two major species live in salt marshes. (Pacific marsh plants differ from those in eastern salt marshes. Several kinds of spartina plants grow in western salt marshes, but other plants are often more abundant. Depending on where a marsh is located along the Pacific Coast, there may be pickleweed, spike grass, sedges, salt rush, tule, milkwort, Pacific silversword, and/or other plants.)

Cordgrass—3 copies
Grows in the low marsh where it gets flooded by water for long periods of time each day and can even be completely submerged by the highest high tides.

Marsh hay—3 copies
Grows in the high marsh where it is flooded only for a few hours each day or even just a few hours each month.

Spike grass—3 copies
As well as blackgrass, salt marsh aster, sea lavender, seaside plantain, and many others, these plants grow alongside the marsh hay in the highest part of the marsh. Spike grass has a high saltwater tolerance and can stand being flooded by the tide periodically.

Clam worm—1 copy
Burrows in mud of salt marsh and as it burrows it secretes slime that "glues" sand grains together and then hardens into a flexible tube. When tide covers the mud, the worm may come out of its tube and swim around looking for food. Feeds on other worms, dead fish, other soft-bodied animals, and algae. Remains in tube when the tide is out. Very tolerant of changes in salinity.

Ribbed mussel—1 copy
Lives half-buried in the mud of the low marsh where the tide floods regularly. Feeds on tiny plants and animals suspended in the water. Breathes with gills. While submerged, pumps water through its body, across its gills, and out again. Filters out food as the water passes through. When left uncovered by water, leaves its shells slightly open so it can continue to breathe. If conditions get too bad, closes its shell completely and "holds its breath" until the tide comes.

Clapper rail—1 copy
Nests in drier areas of high marsh. Feeds mostly at low tide along mud flats and along creek banks in the salt marsh. Eats fiddler crabs, worms, snails, small fish, and other marine animals. Hides in grass of high marsh during high tide.

Salt marsh snail –1 copy
Usually lives in high marsh. Feeds on algae and decaying grass on the surface of the mud. Lacks an operculum, a hard disc most snails have on the bottom of the "foot," which seals off their shell as they pull in. Because the salt marsh snail has no way to seal itself in its shell, during the day it crawls under the mat of dead marsh hay at low tide to keep from drying out, breathes air with a lung and crawls up spartina stalks during the high tide to escape the water. Can "hold its breath" for one to two hours if it becomes submerged.

Raccoon—1 copy
Comes to the salt marsh to hunt. Feeds on crabs, clams, fish, and other animals. Needs fresh water to drink. Leaves the low marsh as the tide rises.

Great blue heron—1 copy
Hunts in shallow water of the salt marsh. Grabs fish with its long, sharp bill. May also eat shrimp, insects, small mammals, and other animals in the marsh. As tide rises, moves higher on the marsh to stay in shallow water, or may leave the marsh completely.

Killifish —1 copy
Lives in shallow waters of the salt marsh. Moves into and out of the higher parts of the marsh with the tides. Feeds on mosquito larvae and other small animals as well as plants. Can withstand low concentrations of oxygen.

Blue crab (Yellow shore crab)—1 copy
Moves into marsh as tide rises. Feeds on worms, snails, oysters, and other marine animals. Moves out of the marsh with the tide. Breathes through gills. If it gets caught in salt marsh as the tide goes out, it will bury itself in the mud and wait for the tide to rise again.

Salt water—6 copies (there should always be more salt waters than other characters)
Comes in with the high tide and rushes out with the low tide. When it comes in, the salinity, or level of salt rises, and if it is a hot day, the temperature cools down. When it goes out, the salinity is lowered and on a hot day the heat rises. In cooler weather, the tides keep the salt marsh from freezing, even if the water is not necessarily warm for people.

Introduce the "characters" of the salt marsh by handing out different slips of paper to different students. Tell students to read them carefully. They should decide on three things that they would like to tell another person about their character. Then, have students go around the room meeting different characters. They should meet three to four different characters and write down each of their three interesting facts (so they should have 9 to 12 facts about salt marsh characters above their own facts).

Closing:

Have students label themselves with the name of the character they are playing, either with simple stick-on labels, with cards around their necks, or with more elaborate costumes, if time permits.

When students have finished, have everyone head outside to an area with some open space. The students playing detritus should find their places first, as the nutrient-rich soil that forms the foundation of the marsh. These students should be relatively spread out in an open area. One side of the space you will use will be a spot for the cordgrass. Explain that in many salt marshes the cordgrass is about the only plant that grows in the low marsh. Have the spartinas stand next to the cordgrass. Then, have the spike grasses and marsh hay stand in. These plants are all part of the high marsh. The animal and salt water characters can stand aside for now.

Tell the group to start off at low tide. The salt-water people should stand at the far end of the cordgrass, away from the other plants. Then say, "The tide is coming in!" Ask the group what they think the salt water characters should do when the tide comes in. (As the tide moves in, the salt water covers the low marsh plants and approaches the high marsh, so salt water characters should walk in among the cordgrass). When they are in their places, say, "The tide is going out!" and ask the group to decide what the salt water characters should do. Try one practice run. Encourage the salt-water people to make sounds like rushing water or crashing surf when they move.

After the tide has risen and fallen once or twice, ask students, Which plants were covered by water for the longest time? (Answer: Cordgrass.) What does this mean for these plants? What conditions do they have to deal with?

Have the animals enter the salt marsh. First, have the ribbed mussel, fiddler crab, and salt marsh snail enter the low marsh. Then, have the great blue heron, clapper rail, and raccoon join the high marsh. Ask these students where they think they would stand in the marsh at low tide. What about at high tide? Now ask the clam and the killifish to stand in the ocean. Ask what these two would do at low tide. At high tide?

Begin again at low tide. Cue the salt-water characters with, "The tide is coming in!" And then, "The tide is going out!" Go through this a couple of times.

Suggested Student Assessment

Locate and show students pictures of a mangrove swamp, and ask students to research how it is different from a salt marsh. How is it similar? Have students research the animals found in mangroves and draw pictures of each species for its own card. Then have them make a different "play" with their mangrove swamp cards.

Extending the Lesson

Have students create two salt marsh murals, one at low tide and one at high tide, using paint, crayons, markers, cardboard, construction paper, corrugated cardboard for cordgrass, etc.

Break students into groups and have each group research a different salt marsh plant or animal. The group should determine how each plant or animal deals with: the wet conditions, high or low salinity levels, changes in temperature, or any other conditions they determine are important (lack of oxygen in the soil, for example).

Have students choose a migratory bird species that visits the salt marsh. They should then determine its habitat requirements, i.e., where it nests, feeds, etc. (for example, the great blue heron hunts for fish at low tide in the low marsh). Tell them to write a short travel article that will make this bird want to visit their local wetland. (If the students live near a salt marsh, have students write an article inviting this bird to the low marsh or high marsh.) Students should try to contrast their local wetland with the salt marsh (e.g., "Tired of all that salt in your bill? Need a break from all the scurrying away from the tides? Come visit our swamp.") Ask: When would this animal visit this area? Why would they want to? Tell students to try to make the area sound as appealing as possible. They should include descriptions of plant life, water conditions, etc., and should not choose a site where the animal could not survive (for example, the killifish would not be able to visit the high marsh unless the tide was very high, as in a storm).