The Great Barrier Reef is the largest system of coral reefs in the world, stretching more than 2000km off the north eastern-coast of Australia. It is said to be like a large living organism. Experts suggest that parts of the reef could be as much as 18 million years old, but most of the coral visible today have only developed over the past 2 million years. As a result, it is an irreplaceable resource and one of the world's greatest natural assets. It is available for the use and enjoyment of all people, but there is a creature that threatens this natural resource.
The Crown-of-Thorns is a starfish that threatens the ocean life in this area. A glance at the crown-of-thorns starfish explains how it got its name, as it is covered by thousands of spines. The spines are extremely sharp and are known to have a toxic reaction in humans. This animal is also the largest starfish in the world. People have sighted ones as big as 700mm in diameter from one tip to the other. The normal size for this starfish is between 250mm and 350mm. This starfish is quite beautiful when it is seen in its natural environment, as it is multi coloured ranging from purplish with ted tip spines to having a green body with yellow tip spines.
The crown-of-thorns also has many other characteristics, which includes a mouth surrounded by short blunt spines, a stomach and hundreds of tiny feet that can be seen form under each arm. The crown of thorn's diet mainly consists of coral. Foods range from soft corals and gorgonians (sea whips) to echinoids (sea urchins), clams and algae. They have also been observed to eat each other. The crown of thorns starfish is capable of going for relatively long periods of time without food. In the laboratory they have gone for as long as six to nine months.
The crown of thorns starfish is a predator that eats other living animals. It is able to move across the coral reef using its suckers to find new prey. After finding a suitable coral it sucks away the polyp's tissue, leaving only a white coral skeleton.
When the crown of thorns starfish is present in large numbers, it often eats together in groups called aggregations. In recent years crown of thorns aggregation have caused large scale coral destruction in other areas of the Pacific, but especially in the Great Barrier Reef.
A female COTS (crown of thorns) releases millions of eggs each year but usually only a very small number survive to become mature starfish. However, if conditions are favourable, it may allow more larvae to settle on the coral reef and to survive. This then can lead to a population explosion on the reef.
The outbreak of this starfish on the Great Barrier Reef has probably been the most extensive of all those recorded in the Indo-Pacific region. The last serious outbreak in the Great Barrier Reef occurred in 1991/1992. It was predicted to occur in 1994 but came 3 years early. These outbreak cause drastic destruction to the corals leaving some areas totally dead.
Large aggregations of starfish will drastically alter the amount of hard coral on the reef. Most hard corals will be eaten, though remnants are often left behind which can regenerate. Coral reefs can recover from the damage done by outbreaks, but it can take up to 20 years just to have a good coral cover again. That is why researchers are finding ways to prevent outbreaks in the first place.
A natural control is the Giant Briton shellfish Charonia Tritonis. The Briton is one of the rare marine creatures that can feed on adult crown of thorns.
Various organizations, including the Great Barrier Reef Marine Park Authority, the Australian Institute of Marine Sciences are conducting research on the crown of thorn starfish. As a result, biologists know that when starfish larvae hatch they may drift. They can drift for up to 400km from their point of release. The spread of plagues
may therefore be the result of the passive transport of larvae in the ocean currents.
From other field and laboratory observations and experiments biologist now know how and when the crown of thorns breeds, its growth patterns, food preferences, feeding habits and some natural predators. Research has also shown that reefs can recover reasonably well within ten to twenty years after major damage has occurred. Many reefs though can be re-infested with before recovery is complete. This has caused some scientists to speculate that continued re-infestation might result in reefs becoming devasted for long period of time.
The crown-of-thorns starfish are a threat to the environment on the Graet Barrier Reef, but the problem can be solved with time, lots of work and monitoring by biologists and researchers in the region.