One of the most commonly known sea stars that has invaded the Great Barrier Reef is the crown-of-thorns starfish.
This is one of a few animals that feed on living coral tissue. It gets its name from the dense covering of long sharp spines covering its upper surface.
The crown-of-thorns is a predator; that is, it eats other living animals.
After finding suitable coral, the crown of thorns pulls its stomach out through its mouth (a process known as stomach eversion) over the coral polyps and releases digestive juices onto the coral, breaking down the polyp tissue into a readily absorbed ‘polyp soup’.
It leaves only a white coral skeleton which is soon invaded by algae, worms, boring molluscs or reef settling organisms.
Researches have shown that chemicals released during the digestion of corals can actually attract other starfish to a feeding site. As the number of starfish feeding in an area increases, the ‘smell’ of digested coral may increase and so recruit still more starfish into the feeding group.
The crown of thorns phenomenon is not unique to the Great Barrier Reef. In recent years crown of thorns aggregations have caused large scale coral destruction in other areas of the Pacific.