4.5 Underwater habitats

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UNDERWATER HABITATS


Curriculum Alignment ACT ELAs 14, 18, 19, 22 NSW KLAs Years K-6: Science and Technology, HSIE Years 7-10: Agriculture, Science, Geography Years 11-12: Agriculture, Geography, Biology, Earth and Environmental Science, Society and Culture QLD KLAs SOSE, Science, Geography SA ELs Futures, Interdependence, Thinking VELS Science, Thinking Processes, Geography

Objectives
>Students gain an understanding of the various forms of underwater habitat and the wildlife that make use of them
>Students learn about human induced impacts on river habitats and their associated plants and animals

Duration
1 hour

Materials required
>Aquatic animal cards (see below)
>Benthic macroinvertebrate poster (can be obtained from a local Catchment Management Authority or state natural resource management agency)
>In-stream habitat scenarios (see below)
>Homework sheet – Match the species activity sheet (see below)

Background
It is important to understand the nature and quality of underwater (in-stream) habitats, because these are a major factor determining the types, distribution and abundance of aquatic wildlife such as fish, platypus and invertebrates. Other factors include flow patterns, water quality, food supply, run-off and impacts from the riverbank and floodplain, competition between species for space and food and predation.

Not all streams provide the same types of habitats. The type and number of microhabitats vary naturally between and along streams. Major differences are apparent when

Old trees creating snags like this provide vital habitat for native fish. Photograph: Bill Phillips

rivers at higher elevations are compared with those lower down. Rivers with rocky substrate and fast flowing through confined spaces have very different fauna to those that meander and wind across flat, open floodplains.

In the absence of suitable habitat very few species will be found even in waterways with good flow and excellent water quality. Generally the greater the variety of habitats in a waterway the greater the number of species found.
The different habitats provided by mud, cobble stones, woody debris (snags), rocks, and submerged and floating plants are readily used by a range of aquatic life for shelter, rest and feeding.

Unnatural inputs to the river (such as farm or urban pollution or sediment from soil erosion) and waterway interferences (like straightening, de-snagging, dam construction and water diversions) can significantly degrade in-stream habitats.

Rivers contain a range of habitat types for aquatic wildlife. The following are among the most common:

>leaf litter and small woody debris
>large woody debris and fallen trees (snags)
>pools, runs, riffles, rapids, cascades and waterfalls
>sand, mud, pebble, cobble, boulder and bedrock substrates
>edge and in-stream reeds and rushes.

Vocabulary
Microhabitat
Substrate
Pool
Riffle
Run
Glide
Channel
Snags
Sediment

Namoi River near Boggabri, NSW, during dry times, but highlighting the complex underwater habitat of pools and snags when the river has more water. Photograph: Milly Hobson, I&I NSW

Lesson plan
1. Using the Benthic Macroinvertebrate Poster review with the students the riffles, runs and glide habitats (see Glossary if necessary).

You can do this activity
i the classroom using
the poster or down at
a local river or stream.

2. Point out other aspects of in-stream habitat such as submerged wood (snags), pebble, mud or cobble stream bottoms, and reeds and rushes growing in the water.

3. Ask students to speculate on what these microhabitats might offer aquatic wildlife.

4. Give each student an aquatic animal card (see below). Ask them to familiarise themselves with the needs of their animal (as given on each card) and draw the animal on the card.

5. Ask the students to stand in a circle or at their desks. Read out or distribute In-Stream Habitat Scenario 1 (see below). Get the students to sit if they think the habitat needs of their animal have not been met.

6. Review which animals are still alive and which are not. Write ‘Scenario 1’ on the board (or notepad for further review back in the classroom) and list the survivors.

7. Repeat this process for In-stream Habitat Scenarios 2 and 3. Ask students what trends they detect. How are the animals doing which have more general needs verses those with specific needs? What could be done to reverse the trends which are emerging?

8. Ask the students to create their own scenario for the Return of the River’. What would they do to bring back the animals that have been lost?

Rocky bottom, shallow water habitat (top), and wider more open channel with healthy aquatic plant community (below). Photographs: Bill Phillips

Extension
Have students create a mural of their local stretch of the river or stream that shows both the concerns along the river for wildlife and ways people can return the river to good health.

If students have set up an aquarium for the native fish lesson (see Module 1 in Part 2), encourage them to add complexity to the habitat.

Have them observe the changes in the fish’s behavior, including the ways smaller fish may use rocks, plants and hiding places for protection.

Ask students: “Could more fish be added of varying sizes if the habitat is more diverse?” and “What does this mean in terms of community diversity in the wild?”

Secondary path
Have students take on an independent or group project on their nearby river, stream or wetland. This may be participating in a monitoring program or joining a landcare group doing weed control or other habitat development work.

IN-STREAM HABITAT SCENARIOS

Scenario 1: Before settlement by Europeans
Australian rivers were complex systems of riffles, glides, runs and deep pools moving over gravel, sand, mud and cobbled river bottoms.

The rivers ran unimpeded from cold swift mountain streams down to slow moving low-lying floodplains. Seasonal floods allowed aquatic animals to migrate easily up and down to find good habitat and spawn. The rivers dried yearly creating isolated pools along the floodplain which were excellent breeding areas for frogs. Large fish passed the dry summers in chains of deep pools in the river channel.

Water temperatures rose and fell seasonally, and provided cues for fish to spawn and grow. Trees covered the slopes, controlling erosion and keeping the water clean and clear. When they fell, they became snags in the rivers and created complex in-stream habitats. Introduced pest species such as Carp, trout, Redfin perch and goldfish were unknown.

Scenario 2: Europeans arrived
Europeans arrived and began to modify the landscape, especially near the coast and along large rivers. Wood and debris were removed from the waterways to make them more navigable for boats.

Some land was cleared for grazing and farming causing erosion and nutrient run-off into rivers. Seasonal flooding and drying continued, prompting spawning and providing safe habitats for frogs.
The cold upper reaches of rivers were largely unchanged, and temperature fluctuations remained stable. By 1908 Carp, goldfish, Redfin perch and Brown trout had been introduced to most rivers.

Scenario 3: Damming the rivers
This began in the early 1920s with the creation of Burrinjuck Dam, the Snowy Hydro Scheme in the 1950s and continued through the 1970s. Flood events largely ceased, and releases from the dams were irregular and often unseasonably cold. Passage up and down the river was severely restricted by dams and weirs and low flows.
Without floods to scour out the rivers, cobbled and rocky river bottoms were often covered with sand and mud. Trees near the river died back as the lower water levels left many high and dry. Large fish were trapped in deep pools and were unable to migrate and breed.

Grazing pressure and land clearing increased, causing more nutrients and soil to end up in the rivers. Demands for water increased meaning both the seasonality and volumes of flows were altered.

Wide, shallow, sandy and rocky substrate river (top) contrasts with the wide, deep, reed and healthy Red gum-dominated river (below). Photographs: Bill Phillips


Downloads AQUATIC ANIMAL CARDS HOMEWORK SHEET