Ewan McDonald visits an island where humans come a distant last to wildlife.

We know where we're going but we don't know what we've seen. Is that dark speck on the deep blue ocean land, or the shadow of a cloud passing over the waves?

Within moments we're right above the green bush and gold sand of a tiny, perfectly circular isle. A dozen tourists scrabble for cameras, phones, iPads to snap their first glimpse of the Great Barrier Reef.

Simone, the pilot, circles a couple of times for photo opportunities, then drops the Cessna on to the grass landing-strip that runs the length of the island: a mere 600m. The plane uses about 595 of them.

We clamber down stairs and are met by a turquoise-shirted staffer. She won't let us move until we understand the unique 45ha of coral and bird droppings that is Lady Elliot Island.

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Seemingly floating rather than anchored to the seabed 85km northeast of Bundaberg, the tiny "cay" is the southernmost point of 900 landfalls and 2900 reefs stretching 2300km, almost to Papua New Guinea; the world's biggest living structure, the only one visible from space.

Lady Elliot is a resort with a difference and a serious purpose. This island has been around for 3500 years but the past 10 and the next 20 could be its most important.

For now all we need to know is that there is no cellphone reception, that internet is intermittent. Traffic - on foot, in reef shoes - gives way to 100,000-plus seabirds that nest here over summer. On land or in sea, turtles rule; this is one of their most important breeding grounds.

A green turtle floats past under the watchful eye of a snorkeller at Lady Elliot Island. Photo / Supplied
A green turtle floats past under the watchful eye of a snorkeller at Lady Elliot Island. Photo / Supplied

For the next few days we will be living in one of the world's most delicate ecosystems. Smack-dot in the "Green Zone" of the Great Barrier Reef Marine Park, the law is "no take" - you can't pick up a shell, rock, flower, much less drop a soft-drink can.

Every morsel of food, every remnant of rubbish must be flown in and out; virtually all power is solar.

The priorities are reef fish, turtles, seabirds; the island's totem, the 5m-broad manta ray; and the reason for the island's existence: coral.

Somewhere further down the order of importance: humans. Only 150 of that predatory species are permitted to stay here on any night; 100 others can come and go during the day.

By Australian standards, Lady Elliot is a human-friendly environment. No mammals, few insects and no jellyfish, great white whatchamacallits or slithering things. "You can snorkel here all year round," said Elana, the Kiwi marine biologist who hosted our glass-bottom boat tour across the lagoon, "without having to wear one of those Smurf suits."

Which is all very well, but I had never snorkelled. I had just been initiated into the art in the resort's saltwater pool.

It felt like practising tai chi in the Chancery: I had the moves but if Jackie Chan abseiled out of the Metropolis for a kung fu duel I was done for.

The pool was 1.4m deep. Elana bobbed around in 14m of the Pacific, without concrete walls, gesturing me to flail from the boat to her. I managed those four strokes. And then ...

I let go her hands and grabbed a rope and inched along the Great Barrier Reef for 250m, looking down into the clear ocean waters at garish fish, coral, a drowsy shark on the seabed ... and a turtle. Asleep, metres below. Back along the rope to the boat. Elana waved for me to take her hands and be guided back to the boat. No. I can do this by myself.

You can walk around the island in 45 minutes. You may see another soul. They will be in another world, just like you. You can dive, let fish feed around your ankles, swim with turtles or rays, chill out around the pool with a book, watch Finding Nemo in the community hall. Or do nothing.

Humans stay in workers' cottages, reminders of when this was a guano mine. It feels like a weekend in a 50s holiday camp in Mt Maunganui or my uncle's bach in the Marlborough Sounds. With the bonus of sensational food, thanks to chefs from my Melbourne obsessions, Cumulus Inc and Cutler & Co. All the more gobsmacking because they are not even allowed to plant herbs in this totally pristine soil.

Sometime around 1500BC a spit of coral rubble appeared above sea level. With the help of bird droppings, it developed into an island over the next 3000 years.

Thousands, millions visited: humpback whales, near their breeding grounds; manta rays, attracted to plankton; sharks and fish. Green and loggerhead turtles lumbered up the beach on which they were born more than 50 years earlier. Two or three months later, their hatchlings scrabbled to safety in the ocean. So did the seabirds.

The next invaders were those pillaging Europeans, in 1805, harvesting the lackadaisical sea cucumber or beche de mer, dried and smoked, exported to Asia. In 1863 the Queensland Government flogged off the rights to mine the island for guano. Within 10 years, all but eight trees had been felled, a metre of topsoil and bird-droppings carted away. Virtually nothing grew, birds boycotted until 1966 when lighthouse staff replanted the island.

Lighthouse keepers and their families had lived here since 1866. The modern version, 21m tall, six beams shining 40km out to sea, is solar powered and automated.

Businessmen cleared an airstrip in 1969 and created a resort; that lease came up for renewal 10 years ago.

The tender was won by three Gold Coast businessmen with a vision for Lady Elliot to become a largely solar-powered, bird- and marine-friendly environment.

They have been granted extensions for another 20 years.

There may be debate about whether the powers-that-be in Canberra and Brisbane are safeguarding the reef - Barack Obama rebuked them at the recent Cairns G20 summit - but in the Green Zone its future is black and white.