Narrator: Listen to part of a lecture in a Marine Biology class.
Professor: We've been talking about the decline of coral reefs in tropical areas all over the world...um... how natural and man-made stresses are causing them to degrade, and in some cases, to die.
So now let's focus on a specific example of a natural predator that can cause a lot of damage to coral reefs—the Crown of Thorns, or CoT starfish.
The Cot starfish is found on coral reefs in the tropical Pacific Ocean and it eats coral.
Now, in small numbers, the starfish don't affect coral reefs dramatically.
But periodically, starfish population explodes.
And when that happens, the reefs can become badly damaged or even destroyed, something we are trying very hard to prevent.
For example, during the 1960s, there was an outbreak of CoT starfish in the Great Barrier Reef, off the east coast of Australia.
Luckily, the CoT starfish population gradually declined on its own and the reefs recovered.
But we were left wondering—what cause the population to increase so suddenly?
Well, over the years, we've come up with a few hypotheses, all still hotly debated.
One hypothesis is that it's a natural phenomenon, that the starfish naturally undergo population fluctuations following particularly good spawning years.
There are also several hypotheses that suggest some sort of human activities are partly responsible, like fishing.
There are fish and snails that eat starfish, particularly the giant triton snail, which is the main predator of the starfish.
These fish and snails have themselves experienced a decline in population because of overfishing by humans.
So with a decline in starfish predators, the starfish population can increase.