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ecology green island


The ancient coral cay of Green Island is a very unique indeed. Out of the 300 sand cays on the Great Barrier Reef it is the only one with a rainforest. Formed around 6,000 years ago by a build up of sand sediments, animal and coral deposits it’s become home to a diverse range of flora and fauna. It sits 27kms from Cairns on the north-western edge of the reef flat in what’s called an ‘inshore patch reef’.

A Protected Area

The Australian government recognises that Green Island is a very special place and has protected it in several ways:

  • The island is a National Park and all commercial activities are regulated by permits.
  • The reef and underwater habitats are part of the Great Barrier Reef Marine Park.
  • Both Green Island and its reefs are included in the Great Barrier Reef World Heritage Area, which gives it international protection under UNESCO.

Island Formation

Sand cays are islands that form on top of existing reef structures – they are basically large piles of sand, coral rubble, broken shells and other reef debris. Wave action pushes the rubble debris into a pile on the leeward, or calm side, of a reef flat. If conditions are just right, this pile of rubble grows into a small sand island.
Seabird droppings help cement the sand together so that it will not wash away with tides. They also provide nutrients for germinating seeds that wash onto the island. Over time, if conditions remain ‘just right’, the island can develop a complex ecology.


The exact age of Green Island is unknown however best estimates are that it is about 6,000 years old. Scientists know that all sand cays on the Great Barrier Reef formed since the last Ice Age, about 8,000 years ago, when low sea levels destroyed all previously existing sand cays.


Green Island’s climate is tropical, with a wet season (January to March) that brings an average yearly rainfall of over 2 meters. Mean air temperatures vary between 24°C – 31°C in summer (November – April) and 19°C – 23 °C in winter (June – August).


Island Bird Life
Island Marine Life

More Great Barrier Reef Information