Finding Nemo

White-tipped reef sharks are very sensitive. They hunt by detecting the vibrations caused by the heartbeat of a sleeping fish.

Dive instructor Nessie is sparing no detail as she briefs our group of divers before we plunge into the depths of Hardy Reef in the Coral Sea. The shark reference makes me conscious of my own heartbeat, which is already pulsating much faster than a drowsy fish's.

I have joined a full-day cruise to the Outer Barrier Reef on a Fantasea Cruises air-conditioned, high-speed catamaran. Within two hours of leaving the Hamilton Island marina we are moored alongside Fantaseas Reefworld, a huge permanently moored pontoon on the edge of the beautiful coral gardens of Hardy Reef.

The 150 passengers soon disperse around the pontoon, some boarding a semi-submersible to view the underwater world in comfort, while others take scenic helicopter rides, go snorkelling in guided groups along marked trails or simply lie back and relax on the upper sun deck, enjoying a cocktail and perhaps a soothing massage in Harmony Hut.

Children have great fun in their own swimming enclosure, snorkelling area and waterslide. If they lack confidence there are grab ropes strung across the surface along the snorkelling trails. Pre-schoolers enjoy fully supervised time doing craft activities and playing games in Club Seahorse.

Throughout the day the platform is a scene of vibrant colour and spontaneous fun. The swimmers and snorkellers are decked out in pink or yellow lycra stinger suits and carry multicoloured flotation aids. No-one goes hungry, either, because the Fantasea staff serve a light breakfast, barbecue buffet lunch and morning and afternoon tea.

There is an option to take an introductory or certified scuba dive.

Our group has had some diving experience, but we will be swimming into a steady current at 16m depth on the face of a 60m drop-off, which offers some challenges. We will need to keep finning continually to maintain forward momentum and must also avoid contact with the jagged edges of coral outcrops, which are easily dislodged and broken.

Once we are geared up we descend a set of steps to a metal platform ingeniously rigged underneath the main pontoon. It's a simple matter to slip into the water and follow a mooring rope to the seabed, where there's an impressive array of hard and soft corals.

George, the resident Queensland grouper, glides regally around us. He is close to 3m long and weighs 350kg.

Yellow trevally hover around his mouth and suckerfish (remoras) maintain station under his portly belly.

In the Technicolor dream-like world that bursts into my vision I have to hunt around for a while until I find Nemo, in his reeftop sanctuary with his colourful clownfish friends. Nemo is quite at home among the stinging tentacles of the anemone clusters.

Nemo is both remarkable for his Hollywood fame and his ingenious method of protecting himself by covering his body with the same mucus that his blind anemone host uses. Each anemone feeler has a chemical sensor which makes contact with passing fish and kills them by injecting venom into their flesh. But when a feeler touches a clownfish it senses the mucus and thinks it is brushing against itself.

If the female clownfish of a pair dies, the male will change into a female, so by the time Nemo was found in the movie, his dad could well have been his mum.

A parrotfish mooches along in a slow-motion parade of blue, red, gold and orange. He has an equally intriguing survival technique; by sleeping in a cocoon of spun mucus he keeps any telltale smell away from predators. We see coral trout, spangled emperors and giant trevally. They are accompanied by tiny cleaner fish, the barbers and groomers of the reef, dining off skin parasites in the mouth and gills with the co-operation of the host.

The colourful array includes curious creatures like wobbegongs, sweetlips, potato cod, pipefish, goatfish, butterfly fish and blennies. I come face to face with a giant Maori wrasse and willingly concede right of way. I spot a green turtle paddling along at a leisurely pace, content in the knowledge that he has 100 years to complete his life's work.

As I drift over the precipitous drop-off, I can readily identify vivid examples of staghorn, lunar, brain and honeycomb coral, along with brittle stars, spiny urchins, sea cucumbers and a giant clam and green turtle but thankfully, no banded sea snakes.

Contrary to popular belief, the Great Barrier Reef is not one continuous structure running for 2000km along the Queensland coast. It is actually a complex tapestry of 2900 individual reefs. There are 350 coral islands, called cays. Only 130 of these islands support vegetation and bird life. A further 680 continental islands are actually the tops of mainland mountains, created when the oceans rose 120m at the end of the last Ice Age.

Remarkably, the massive reef structure has been formed by the near invisible coral polyps, which feed on marine organisms such as zooplankton.

The polyps are prolific breeders and have two reproductive options. One is asexual fragmentation, in which a section of living coral breaks off in a storm and quickly forms a new colony.

The other is coral spawning, which is a spectacular shower of egg and sperm bundles, thrown out simultaneously by millions of polyps. The multicoloured swarms spread out in the current to form new colonies.

I leave Reefworld with a smile on my face. Who could fail to enjoy the experience of sparkling blue waters, cartoon-coloured tropical fish and vibrant coral gardens?

It is a close encounter with an undersea dreamscape and a thoroughly enjoyable, adventure-packed day, experiencing the wonders of the Great Barrier Reef - a kaleidoscope of moving colours and myriad creatures in the most diverse ecosystem on the planet.

Finding Nemo among his sheltering anemones was the highlight of my day on the reef. His endless game of hide and seek is one of nature's great wonders of the deep.

If you go:

GETTING THERE
• Air New Zealand and Qantas operate regular services to Brisbane from New Zealand and Virgin Blue has a daily service to Hamilton Island Airport.

REEF EXCURSIONS
• Fantasea Cruises depart from Shute Harbour near Airlie Beach on the mainland for the 30-minute crossing to Hamilton Island marina. Then head north through the Whitsunday Passage to the Outer Barrier Reef and Reefworld, a permanent floating pontoon moored to the edge of Hardy Reef.

ACCOMMODATION
• Airlie Beach has superb over-the-water suites at the Coral Sea Resort on Ocean View Ave with dining at the excellent Clipper Restaurant. The Airlie Beach Hotel on the Esplanade is renowned for its beachfront Capers at the Beach Bar and Grill restaurant.

WEBSITES
• Tourism Queensland: www.tq.com.au
• Fantasea Cruises: www.fantasea.com.au.

• Paul Rush travelled to Hardy Reef courtesy of Tourism Queensland. He is an Auckland-based travel writer.