Australia’s Great Barrier Reef the World’s largest Coral Reef covering over 350,000 square kilometres. Off Australia’s North Queensland coast in the Coral Sea.
It is the largest coral reef globally, and 1981 was selected as a World Heritage Site because of the diversity of life.
Whales, dolphins and porpoise, 30 species in all have been recorded. Large dugongs live there as well as 1500 fish species.
The Great Barrier Reef and its lagoon offer various habitats for fishes and other marine organisms. The outer part of this massive reef, where the most transparent water is generally found, is divided into zones.
Typically there is a broad outer reef flat, the inner part of which may be covered with fleshy algae and the outer part with encrusting coralline algae. The reef flat is exposed during low spring tides.
Outer Barrier Reef
Coralline algae rim at the outer edge, where the surf breaks, then the broad spur-and groove zone. Subject to strong surge from incoming waves and the scouring action of sand and rubble in the grooves from powerful water movement. The grooves may extend as deep as 20 metres.
Below the spur-and-groove zone, an abrupt vertical escarpment that drops to 30 m or more gradually follows this to the abyss.
Each of these zones has its characteristic assemblage of corals, algae and associated marine life. The channels and passages through the reef, both shallow and deep, provide more habitats for which current is a significant parameter.
On the sheltered side of the outer reef, as the water deepens slightly, there’s a zone of elongate patches of coral, coralline algae, about 1-2 m wide and 20 m or more in length, separated by channels.
Then a broad zone of sand grading into depths of the lagoon. Isolated on the sand substratum, there are usually many small coral heads *called bommies in Australia, each a microcosm of marine organisms.
A variety of coral formations occur within the deeper lagoon, some rising pinnacle-like from the deep water.
Corals growing in the sheltered lagoon water are often delicately branched. Also in the lagoon are broad expanses of sea-grass beds. Brightly coloured corals make the reef appear like an underwater garden.
Moving towards the mainland of Queensland, silty sand and mud habitats tend to dominate the lagoon floor.
The islets and larger islands of the Great Barrier Reef complex provide more habitats, such as rocky intertidal areas and mangrove swamps.
During COVID-19, the number of liveaboard trips departing from North Queensland has decreased. Visitors are best to book in advance to avoid the disappointment of missing out.
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From Cairns to the Outer Barrier Reef