Science for sustainable reefs

Activity 1

Experiment: The impact of catchment pollutants on aquatic species

Many reefs worldwide are situated near catchment areas associated with agriculture, coastal development or mining activities. The high sediment, pesticide and nutrient loads in rivers draining from these catchment areas can affect many reef species including corals, fish, sea grasses and algae.

In groups of 4, design an experiment to test the effect of one of the following on microscopic algae and plant growth:

  • sediment
  • fertiliser
  • nitrate
  • phosphate

Remember you will need a control, replicates and hypothesis for your experiment.

The following equipment will be available:

  • 4 x 250mL beakers or containers
  • digital balance
  • marker for labelling your beakers
  • Pasteur pipette
  • 100 mL measuring cylinder
  • haemocytometer (if available)
  • aquarium pump and air tubing  (if available)
  • microscope
  • 1.5 L pond water
  • sediment suspension
  • sodium nitrate (choose an amount between 1-5g/beaker)
  • calcium monohydrogen phosphate (choose an amount between 0.2-0.5g per beaker)
  • liquid fertiliser
  • 4 x small pieces of pond weed eg. Elodea

Set up your experiment and place your group’s labelled beakers in a sunny position. The experiment should run for 3-4 weeks. At least once a week observe your beakers for:

  • relative algal growth by comparing the colour of water in the beakers using a colour chart (you may wish to create your own chart)
  • density of algae using a haemocytometer (if available)
  • pond weed appearance/leaflet number

What did you find?

Present your results using clearly labelled diagrams, tables and/or graphs.

Answer the following questions:

  1. What effect did your pollutant have on algal growth? Why?
  2. What effect did it have on aquatic plant growth? Why?
  3. How could you improve your experiment?

Although your experiment was conducted in fresh water, these pollutants can have similar effects in coastal waters.

  1. Explain how this change in algal and/or plant growth in a coral reef might affect other reef species? Give at least two examples.

Use the information in Science for sustainable reefs to answer the following questions:

  1. How do you think run-off would affect reef biodiversity?
  2. Would it be necessary to worry about run-off if a reef was threatened by a greater problem of increasing water temperatures? Explain your answer.

Technicians’/Teachers’ notes

  • Preparation of sediment suspension

    • Mix 250g clay and 250g sand in distilled water to make a 1L suspension. Provide each group with 100 mL of the sediment suspension. Instruct students to mix the suspension prior to using it. An aquarium air pump will help to keep the sediment in suspension.

  • Students should use disposable gloves when handling the algal cultures that grow in their beakers.

  • Treat algal cultures prior to disposing of them by adding bleach to the beakers to make a 1% solution. Sit culture overnight then pour treated solution down the drain.

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Posted September 2009