This experiment is designed to test the hypothesis that deep reef corals are darker, because they need to absorb more of the available light. To test this, select different coloured materials and place thermometers under them. Shine a light on the different materials or leave in the sun to see how much energy is absorbed by the different colours.

Activity Steps

1. Make sure that all thermometers are at the (same) room temperature.
2. Note the temperature of each thermometer.
3. Place one thermometer under each of the different pieces of material.
4. Put the thermometers covered by the material under the light source, making sure they are the same distance away (approx. 20cm).
5. Keep the thermometers there for 15 minutes.
6. Note the new temperature for each thermometer.

• 3 pieces of material of varying shades (these could match coral colors - 2 from the shallow reef, e.g. yellow and light brown and 1 from the deep reef, e.g. very dark brown)
• 3 thermometers
• A light source, e.g. a lamp (using an incandescent bulb rather than an energy-saving one, as these emit more waste heat)

Water is like a natural light filter. It tends to absorb colors in the red part of the light spectrum, so it leaves behind the blue part which is why the oceans look blue. The deeper you go, the less light there is, so the darker it gets. But corals have adapted to these harsh conditions: recent research shows there are deep water corals that glow in the dark. The fluorescent corals absorb the little light there is to survive.

Scientists have found that corals can survive in deep water by making a special type of fluorescent protein. This helps feed the zooxanthellae, the symbiotic algae that converts corals’ food into energy through photosynthesis.