Underwater In Australia

There is some redundancy with a late October post about Cairns and the Great Barrier – but this speaks a bit more about the reef and its wildlife.

The Great Barrier Reef is touted as one of the few landmarks on earth that can be seen from space. In fact this remarkable array of atolls, islands, reefs, shoals, and mangroves can be seen from space. The reef consists of more than 2500 islets and reef parts that stretch from New Guinea to the coast off south-central Australia. if you have spent a week diving on the reef you have seen but a tiny fraction of it. The corals, fish, mollusks, and birds make for a most exciting array of life in the warm seas just off shore. 

The reef is about 1600 miles long and has as many as 2,900 reefs and 900 islands associated with it. The reef is in the Coral Sea (appropriately enough) and reaches all the way to Papua, New Guinea. It is a structure that is covered with billions of living architects; each building on the foundations laid by their predecessors. Though the reef has been around for about 25 million years there have been many starts and stops as the continental plate upon which the shallows ride has moved considerably – sometimes to a place favorable to coral growth and sometimes to place not favorable. The current reef creatures probably have an ancestry dating back about 20,000 years though they are building on a previous reef from about 600,000 years ago. The sea has risen almost 400 feet in the that time and the coral has grown with it. Coral reefs can grow upward about 10 inches a year if circumstances demand it.

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. 


coral symphony

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.

2 thoughts on “Underwater In Australia

  1. DavidI am writing to ask permission for the use of pictures from your website on my own. I am a student at Edge Hill university, Lancashire, England. I am creating a website based around the effect of climate change on Australian bird populations.The picture will be clearly referenced on the page it is used on and it would be much appreciated if i can get the go ahead for using this picture. The website is purely for educational purposes and there will be no profit taken from this website that i am creating.it is the first picture on this page and i will link my website to this page if thats any helpMany thanks Tom Holdway


  2. I have tried to reply previously and failed. Perhaps this will work. Yes you can use the images.I have lots of images – what is the purpose of you website; I may have better or more useful images.DEC


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