by M E Skeel

Created on: June 08, 2009

The Great Barrier Reef has so many animals that it is impossible to cover them all here. Fifteen hundred fish species live at the northern end of the Reef in the warmest tropical waters,. Even at the bottom end of the reef there are still over five hundred species of fish. The number of invertebrate species, animals without backbones, is still unknown and must conservatively be in the tens of thousands. Besides the fish and the invertebrates there are also a number of other vertebrate species, including many birds, reptiles and a few mammals.

The basis of the reef ecosystem is the almost invisible coral animal. The coral structures are obvious but the tiny animals that inhabit the plates, staghorns and brain corals are not. These almost microscopic jellyfish-like animals live in the holes in the coral structures, where they feed, divide and create the coral structures by secreting limestone. Within their tiny bodies live the symbiotic algae that create the incredible colors of the corals. It takes thousands of coral animals to make one coral so the total number of coral animals needed to create the entire Great Barrier Reef is mind bogglingly large. Overall there must be billions of the little creatures for this structure to exist and billions more that have lived and died in the past to create the entire structure.

At the opposite extreme are the giants of the ocean, the Humpback whales, who come to the tropical waters to give birth to their young. Other large animals that are sometimes seen in these waters are the salt water crocodile and the gentle dugong or sea cow. None of these species are true reef animals. Crocs inhabit estuaries and salt water rivers inland of the reef. Dugongs feed on sea grass beds closer to the mainland and humpbacks do not feed on the reef because the water is nutrient poor and thus does not support the great plankton blooms found in temperate and polar waters.

When diving on the reef, one has the impression that there are almost no plants. The reef is teaming with animals but what is the basis of the food chain? There have to be producers somewhere. The answer is in the bodies of so many reef animals but in particular the coral animals and the clams. There reside the zooxanthellae, the symbiotic algae that keep the corals alive by feeding them sugars produced by photosynthesis. The little corals do their bit too, filtering the water for waste products and building the shelters that help keep them both

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