Cays in the Great Barrier Reef Marine Park

The seascape of the Great Barrier Marine Park is huge and diverse. It has many species of fish, corals, turtles, molluscs and marine mammals. It holds many mysteries and wonders as well as different types of land masses and reefs.

One of these land masses is a cay - an island made up completely of sand that sits on a coral reef.

While most of the islands in the Great Barrier Reef Marine Park are continental islands (islands that closely resemble the mainland that they were once attached to), cays are completely new islands that have been created and formed by sand deposits over time.

These islands are much more opportunistic and form independent of the rest of the coastline in a somewhat more random way and have a pretty amazing creation story.

How are they formed?

The Marine Park has over 300 cays within its boundaries. The cays form when broken coral, shells, and other debris accumulate on the ocean floor over time through tides and currents. These mounds attract shifting sands and more debris, which eventually breach the surface of the ocean as they grow. They essentially rise themselves out of the ocean and all of a sudden, there is an island where there wasn't one before! Over time seabirds passing over the island or landing on the island will leave enough debris that it will give the cay a start of organic matter. As the matter accumulates and turns into topsoil and nutrients, it begins supporting simple forms of life such as grass and other plants. 

How long does it take for a cay to form?

This process does not happen overnight. It is long and slow just like the formation of any true island. And don't be fooled - cays are a much more stable island than you may think. Just because they are made of sand doesn't mean they will be swept away in a big storm (although they can if it's big enough). They are not like sandcastles on a beach and are more like any other island you can imagine that is stable and permanent. Cays in Australia, such as Heron Island, water systems, resorts and research facilities. The plant life and trees that grow there make the sand dunes and shape of the island stable and less likely to be affected by weather or storms.

Famous Cays on the Great Barrier Reef

You can visit Heron Island which is located south of the Great Barrier Reef Marine Park. It's famous for its nesting turtles that return year after year and lay their eggs in the sandy shoreline. There are also many smaller cays through the Marine Park that you can visit, such as Green Island and Michaelmas Cay, which are often used as a launch point for snorkelling and scuba diving. They are unique in their form and structure and make for a great place to visit and stay while you are in the Great Barrier Reef Marine Park or the rest of Australia.