Estuary Activities

24K image of Mangrove

Visit an estuary. Record as many different microhabitats as you can. Identify and record the plants and animals found in these habitats. Draw an outline of the estuary and trace the water flow at high tide and at low tide. How does the water flow determine the distribution of plants and animals? Spend some time in teams of three being absolutely quiet, observing the habitats to see what sorts of creatures emerge when you don't disturb them. Remember many creatures, like crabs, feel the vibrations caused by just moving your feet and stay hidden. So you have to remain motionless and quiet to see what really lives there.

Estuaries are a good place to study birds. How do birds fit into the flow of nutrients in the estuary? How do different birds segregate themselves into different roles and habitats?

Form a hypothesis on how the body parts of the creatures help them adapt to their specialised habitats. Design a fair test to discover if your hypothesis is correct.

Working together with other students, make a list or poster showing the many different ways we can think of mangrove trees or other estuary creatures. How many different roles do these creatures play in their habitats?

What animals spend only part of their life-cycles in Estuaries? How do their shapes and abilities fit them into their specialised roles within the estuary habitats?

Examine the microflora and fauna of the surface of the mud flats and of the foam that forms on the incoming tide. These creatures are very important as highly productive members of the food web. Develop a project to map patterns of distribution of the microflora in relationship to the tides, fresh water, or silt.

Discuss what happens to the specialised estuary creatures when the estuary is filled in or polluted.

Build a model water catchment system in a sand box. Sculpt the sand into a model of the water catchment system where you live. Use a sheet of plastic to cover the sand and shape the rivers and creeks with your fingers. Have an estuary at the lower side of the box where the water will enter the sea.

Pour water onto the model with a watering bucket (rain) and see how the water collects in the rivers and runs to the sea.

Add "plants" to the system. The plants can be cut up pieces of a towel. Add some mud to the water and pour it over the catchment. Observe how the cloth captures the mud from the water and slows down the water flow.

Identify estuaries in your area from maps. How many of these estuaries have been changed by human development? What changes can you identify in the estuary nearest to your school?

Help with a major scientific effort to measure changes in New Zealand estuaries. To do this, you must determine the extent of estuary plants that exist in an estuary now and see if you can find out how much of the estuary has been filled or otherwise changed in the past 10 years, 20 years or longer.

How to measure habitats in an estuary

The first step is to obtain an aerial photograph and topographic map of the estuary. Contact the local office of the Dept. of Survey and Land Information to order Aerial Photographs of almost anywhere in New Zealand. These cost $10.70 for an 8X10 black and white print, plus $12 handling per order. Enlargements cost from $30. They are available from 1935 on, so you can get a series showing change over time of the estuary you wish to report on. They also have topographic maps that will often show estuary plants and will help orient your aerial photographs.

Before you buy aerial photos, however, check with your Regional Council. Many Regional Councils have aerial photographs of estuarine and coastal areas. These may be available at no cost. Some local libraries have collections of old photographs of great value to seeing long term changes in your area. Be sure to get the date the photo was taken and the scale of the image. Low altitude photos (5,000 feet or less) are best as they show the most detail.

The easiest way to determine the total extent of estuarine plants from the aerial photograph is to very carefully trace the features of the image onto clear overhead projector plastic sheets. Be sure to include at least four distinctive landmarks in your tracing that you can identify in the photograph AND in the real world. You will use these known landmarks to check the scale of your tracing and your measurements, so pick landmarks that you can go to and accurately measure the distance between them (you might ask a surveyor to help with these measurements if you are not sure how to do them).

In your tracing, use a heavy solid line for the shoreline, a dotted line for estuary trees, a dashed line for sea grass beds, and a thin line for the edge of the water channels in the mud flats (if visible in the photo). Include roads and "developed" areas on the shores of the estuary (houses, factories, and farmland) within two centimetres of the estuary shore. Also mark any structures that have been built in the water (wharves, aquaculture farms). Have more than one student team try this and compare the tracings. If there are differences, which one is correct? Make any needed changes and use the best tracing for the next step.

Use an enlarging photocopier to make a blow-up of the tracing, as large as the photocopier can make it. Use graph paper with the smallest sized squares you can find as photocopier paper so your tracing is now shown on graph paper. Make a label in one corner with the name of the people who did the tracing and the date it was done. Include the identification number of the aerial photograph amount of enlargement from the original photograph and the scale of the original photograph (This will be available from the people you got the image from).

Label the landmarks, names of streets or rivers, and other features on the enlarged tracing.

Count the total number of squares within the boundaries of the estuary (This is easier if the graph paper has thicker lines every ten little squares) estimate how much of a square is within the estuary if the line cuts a small square into sections. Count the numbers of squares inside the grass, tree, and water channel lines. Count the numbers of squares inside developed areas along the coast.

You can now calculate the percentage of the estuary covered by each feature. Determine the exact distance (in the real world) between the known landmarks you included on the tracing. Measure the distance between landmarks on the tracing and you can calculate the scale of the tracing (eg. 1-mm = 10 metres). How does this compare with the known scale from the photograph plus the known enlargement factor? Now you can calculate the exact area covered by each square of graph paper and the exact areas covered by trees, sea grass, the water channels and the whole estuary.

Repeat this process in aerial photos of the same area taken in later (or earlier) years and compare the changes you observe. Quantify the changes and write a report on how the estuary has changed.

Record your research in your Sea Keeper Estuary Log Book and keep the tracing in the log book.

Facts about Estuaries