Under the waves

The Great Barrier Reef stretches for over 2,600 kilometers along the seaboard of tropical Queensland, but Cairns is one of the main centres taking tourists out to visit the reef. The reef is about 30 kilometers offshore, so day trips leave port about 9 am, take about an hour to reach the reef, and then anchor closeby to allow people to snorkel, and in the case of some trips, also dive.

The boats leave from the Reef Fleet Terminal on a small promontory at the south end of the Esplanade. There are tens of tourist boats leaving for the reef each day, and the terminal is organised like an airport check-in, where you queue to get a boarding pass before proceeding to the boat.

The boat that I went on took about 30 of us.

The crew were excellent, taking great care that everyone felt confident and safe, whatever their level of experience. The trip out was used to fit us out with masks, snorkels and fins, and instruct us how to use them:

The place that we were headed was Upulo Cay, the pale blob to the south east of the 'C' of Coral Sea:


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A cay is a low sandy island formed on the surface of a reef. Some of them are big enough and high enough to have forest growing on them, but others, like Upulo Cay, barely break the surface. The idea was that we would be put ashore on the cay, and would be able to don our fins there and snorkel back to the boat.

In the event, it was a very high tide, so we were put 'ashore' in a few inches of water.  It wasn't the perfect weather for snorkelling: a strong wind was blowing which created waves, stirring up the sand and reducing visibility in the water. (All of the underwater photos have been edited and give the impression that it was clearer than it actually was.) Photogrpahing the underwater life was also challenging as it was difficult to frame and focus on a subject when bobbing up and down in the waves.

The reef itself is built by corals, small colonial animals that are related to jellyfish, and who create a thin living layer on the surface of the non-living calcium carbonate skeleton which they secrete. The skeletons of different coral species have a range of different forms - from domes to branched 'trees' - which are probably adapted to catching their small floating prey in different strengths of water movement: branched forms are probably more efficient at catching prey, but are also more vulnerable to damage by tidal currents and wave action. The corals have potozoa called zooxanthellae living as guests inside their cells in a you-scratch-my-back-I'll-scartch-yours 'symbiotic' relationship. The zooxanthellae photosynthesize, producing carbon-based chemicals that the coral can use as an energy source. In exchange, the corals provide the zooxanthellae with shelter, nutrients (including nitrogen and phosphorus in their own waste material), and the CO2 that the zooxanthellae need to photosynthesize. The pigments that the zooxanthellae use for photosynthesis are what gives the coral its colour; if the coral is stressed - for example by too high a water temperature - the zooxanthellae die or are expelled, and the coral loses it's colour so the white calcium carbonate shows through: hence 'coral bleaching'. Not surprisingly, coral bleaching is becoming an issue in relation to climate change.

As well as the coral (amd small coral reef fishes), there were other creatures such as this ray ...

... a striking blue starfish ...

... and some of its relatives, sea cucumbers:

The biggest group of fish was the school under the back of the boat: sleek silver fish of the open sea:

Once we were all back on the boat, it moved to a new anchorage, and people had the opportunity to snorkel from the boat. It certainly seemed a long way from any land:

Another option was to dive: those with a PADI certificate could dive unsupervised, but for beginners there was the chance to dive with an instructor. I have dived before - but over 30 years ago, and also then only with an instructor - so I definitely counted as a beginner. There was one other beginner, and we had one instructor - literally - between us:  he held onto each of us by the hand for the whole 30 minute dive.

After the dive, there was a break for a leisurely lunch ...

... and after lunch another chance to dive.

This time I and my fellow diving neophyte were allowed 'off the lead' and got to follow the instructor instead - although he did keep a beady eye on us:

We didn't go very deep on either of the dives, which was fine by me as there was plenty to see: more coral of course ...

... including this fluorescent blue one ...

... coral reef fishes ...

...  a giant clam about a meter across ...

and some sponges:

These colourful little guys - or rather guys'n'gals as they're hermaphrodites - look very similar to sponges and have a similar lifestyle - filter-feeding small organisms from the water. However, they're a totally different group of animals - sea squirts - whose nearest relatives are the vertebrates: fish, amphibia, reptiles, birds and mammals - including you and me.