'Acanthaster planci," a thorny brown-colored invertebrate, is a major predator of coral polyps. Using its tube feet, it moves across coral reefs in search of suitable prey. When it spots an appetizing coral colony, it pulls its stomach out of its mouth (stomach eversion) and places it over the coral polyps. The stomach's digestive juices then break down the polyp's tissue into a consumable 'polyp soup.' Only the white coral skeleton is left which is soon invaded by algae, boring mollusks or worms that eventually break it down into small fragments.
REEF TYPES:
There are few mainland fringing reefs along the Queensland shore since large amounts of freshwater and sediment discourage significant coral growth. However, they are more commonly found around the high continental islands where the water is clearer.
WATER MOVEMENT AND CORAL GROWTH:
Since tides are influenced by both the sun and moon, tidal ranges change with the seasons. Throughout the Barrier Reef, the range between high and low tide is greatest at the equinoxes. In the northern reef the influence of the sun is greater. Summer tides at night, in January and February, and daytime winter tides, in June and July, are very low. The low summer tides cause greater widespread death of coral and other organisms than in winter because heavy rains occur at the same time. This reduces salinity below tolerable levels, having a greater impact than the extended exposure to solar radiation of the winter tide.
MAN AND THE REEF:
Today the reef plays an important role in many more people's lives. Many earn a living from commercial fishing or from the all important tourist industry. With the substantial increase in human activity on the reef, concern has grown over preservation of its natural heritage. This resulted in the passing of the Great Barrier Reef Marine Park Act in 1975 which created a protected Marine Park covering more than 200,000 square miles and a generously-empowered park authority to oversee its management. The Great Barrier Reef remains in a relatively natural state in comparison to other reefs that have suffered from uncontrolled human activity and its pollution.
