The reefs are constantly growing, breaking, and being relocated. The coral is hard but not permanent. Fragments are created by fish, storm action, and changes in water chemistry. The bits and pieces are then washed about by the sea. At some point they begin to accumulate and form a shoal/ Eventually the shoal is visible above the sea and then come the steps that make it a real island; the adding of more material, a harding of the particles, the arrival of birds, and the arrival of vegetation. This evolution is not always step by step as a storm can scatter the materials erasing all signs of a once-promising island.
There are about 600 types of corals in the Barrier reef System. Most are hard corals but there are many kinds of soft coral as well. The fishes run to about 1500 species and there are about 125 species of sharks. The little things are also of interest; the Box Jelly is a smallish jelly with very poisonous tentacles. There are also octopi, cone shells, and a few fish that harbor toxins. But contact with any of these is very unlikely.
giant clam amongst corals – this species can grow to be about four feet in length
and about three feet vertically
The birds are an important part of the reef. their droppings, when mixed with the calcium products piled by the sea, provide the chemicals to form the hardpan that seals the islands and allows them to hold fresh water. These fresh water areas are then suitable for the arrival of plants. So the transition from broken coral to part of a vegetated island is rather long and involved.
The two main species of terns out on these islands are the Brown Noddy (above) and the Sooty Tern (below). The populations of these two are augmented by Crested and Lesser crested Terns, a few Silver Gulls, and the occasional Brown Booby. Many of the nesting islands will harbor 5-10,000 pairs of sooties and noddies. These are birds that only come to land to nest; otherwise they are pelagic.
The bird below looks a great deal like the Sooty Tern. The Bridled Tern has a longer white stripe at the eye and a more charcoal plumage. they are few and far between in the reef but they are always a treat to see.