The long-spined sea urchin (Diadema antillarum) is an important herbivore that helps maintain the health of coral reefs.
Marine biologists used a choice chamber to investigate the effects of constant light and flashing light on the movement behavior of Diadema antillarum.
Table 1 shows their results. The P values show results from a chi-squared statistical test.
Table 1 | Behaviour of Diadema antillarum | Type of light used in choice chamber | | :--- | :---: | :---: | | | Constant | Flashing | | Moving towards the light | 14 | 24 | | Moving away from the light | 36 | 26 | | P value | 0.01 | 0.58 |
State a null hypothesis the marine biologists tested in this investigation.
The natural habitat of Diadema antillarum is coral reefs of tropical oceans. Suggest two factors (other than light) that should be kept constant in the choice chambers so that the sea urchins display normal behavior.
A researcher studying Table 1 suggested that either type of light could be used to cause Diadema antillarum to move away from the light. Evaluate the researcher's suggestion.
At sunrise, Diadema antillarum move rapidly away from light into deeper reef crevices to hide from predators. Table 2 shows the maximum speeds recorded of these sea urchins.
Table 2
| Response to light | Maximum speed / mm min−1\text{mm min}^{-1}mm min−1 |
|---|---|
| Urchins moving towards constant light | 150 |
| Urchins moving away from constant light | 320 |
Calculate the shortest time one Diadema antillarum would take to move from an exposed shallow reef at 6 m6\text{ m}6 m depth to a deep reef crevice at 42 m42\text{ m}42 m depth at sunrise. Give your answer to the nearest hour.
