Competition
A coral reef is a good place to look for examples of competition.
Read through this description of coral reefs and the questions and answers which follow.
Most tropical seas are surprisingly short of life because they hold fewer minerals than colder waters. In tropical shallow seas, where the water temperatures are above 18°C, coral reefs can develop. The main species there are corals, which can grow in waters of up to 30m deep. Corals are animals but they have algae inside their cells which can photosynthesise. Corals feed by filtering small floating pieces of food and on the food that leaks out from the algae in their cells.
Large and complicated food webs are built up around a coral reef, with many animals feeding on the coral itself, and others feeding on these. Yet other animals feed on scraps and particles in the water. Around a coral reef higher levels of minerals can build up.
In the 1960s and 1970s many areas of the Great Barrier Reef in Australia were destroyed by crown-of-thorns starfish. These starfish feed on coral and their population numbers had exploded. This was thought to be linked to the collection of triton shellfish or the overfishing of trigger fish and puffer fish. Another suggestion was that the coral was already weakened by pollution.
Question 1
Name two factors for which the coral or the algae inside its body must compete (2 marks).
The Answer
The coral or the algae must compete for food particles and oxygen.
Examiner's Note
This answer is correct and would get two marks. Other possible answers are that the algae compete for light and carbon dioxide. The corals also compete for places to attach themselves.
Question 2
Triton shellfish, trigger fish and puffer fish are all predators of young starfish. Explain why over-collection of these species led to the destruction of the coral (2 marks).
The Answer
The over-collection of these species meant that there were no predators of starfish, and more starfish meant that more corals was eaten.
Examiner's Note
Well done. Notice too that triton shellfish, puffer fish and trigger fish are competing to eat starfish. This is not needed in this answer but is another example of competition.
Question 3
Suggest why the coral might be particularly vulnerable to pollution (1 mark).
The Answer
The coral is particularly vulnerable to pollution because it grows in shallow water where the pollutants are not diluted.
Examiner's Note
This is a good suggestion. Looking at the passage you can see that corals feed by filtering small pieces of food, so they will tend to catch any particles of pollutants very easily, so an alternative answer would be that these will concentrate in their bodies and kill them.
