Lord Howe Island: Life on Lord Howe
The dainty anemonefish of Lord Howe Island is becoming an early-warning system for rising temperatures.
OUR SMALL VESSEL GENTLY rocks on the southern reach of the Lord Howe Island lagoon. A breeze whispers around two rainforest-clad mountains, their flanks dropping precipitously to the sea. Looking over the side of the boat, it’s possible to make out every inch of the reef, including riotous brigades of brightly coloured fish. Among them I hope to find Lord Howe’s very own Nemo, the McCulloch’s anemonefish, which is found only in and around this idyllic puddle.
Enclosed by the world’s southernmost barrier reef, Lord Howe Island is 1000km south of the Great Barrier Reef and 780km north-east of Sydney. In 1982 the Lord Howe Island Group (comprising Lord Howe, Admiralty and Mutton Bird islands, and their surrounding marine environments) was World Heritage listed. Within 20 years the island’s underwater world was further protected in the 3485sq. km Lord Howe Island Marine Park, which encompasses both State and Commonwealth waters.
And it’s little wonder. The marine environment of this isolated speck of NSW is renowned for its populous mixture of tropical and temperate species delivered on converging currents. In these rich waters, cool-water species such as New Zealand fur seals mix with hordes of green turtles that have hitched a ride from the Great Barrier Reef on the East Australian Current (EAC) to set up home. This is the most southerly point in the range of many tropical fish. And 16 fish species are found nowhere else on earth but in this ecological hotspot.
In the lagoon, the water is so clear it's possible to conduct our research simply by looking over the side of the boat - but where's the fun in that? At this first survey site, Jean-Paul Hobbs, a marine biologist at Queensland's James Cook University, can barely contain his excitement. "The project is simple," he says. "Monitoring all the species on the reef can be overwhelming, so we focus on a single species - such as this anemonefish - which acts as an indicator species. Global warming can kill corals and anemones, and anemonefish can't survive without anemones. By monitoring this species we get an indication of how healthy the reef is."
Jean-Paul's project doesn't stop with his three-member research team, which includes me and fellow marine biologist Joseph Neilson; the community of Lord Howe Island is also involved. Students at the Lord Howe Island Central School, employees of the Lord Howe Island Marine Park and three glass-bottom-boat tour operators are assisting in the inaugural anemonefish survey, donning masks and snorkels to count on an annual basis the number of anemonefish. They recognise the importance of conserving the Lord Howe Island reefs for future generations.
Lord Howe Island: environmental jewel
One of the tour operators, Dean Hiscox, explains the strong connection he and fellow locals have with the reef. "Without it we'd lose both an environmental jewel and our livelihood," he says. Another benefit of this collaborative project is education. "We have a great opportunity to teach visitors about issues such as global warming, bleaching and the unique features of the region - including the McCulloch's anemonefish. It's great to see people's eyes light up when the message gets through to them."
"This project has really allowed our staff and students to learn more through first-hand experiences," says school principal Julian Mostert. "We didn't realise the marine creatures on coral reefs were in so much trouble."
Sea anemones, like hard corals, have a symbiotic relationship with a species of algae called zooxanthellae. The anemone provides shelter for the microscopic algae, which in turn provide carbohydrates to the host as a by-product of photo-synthesis. When anemones experience an increase in water temperature, the food-producing algae may be expelled. Zooxanthellae provide the anemone with its bright colours, so when they're expelled the anemone appears pale and bleached and, if the zooxanthellae are not reabsorbed, it eventually perishes. Anemonefish are entirely dependent on the availability of suitable host anemones for habitat and protection - a loss of anemones results in a loss of anemonefish.
Occasionally, complete reefs can be affected by an increase in temperature. This phenomenon, known as a mass bleaching event, has been reported throughout the world's tropical waters, most recently in the summers of 1998 and 2002. The Great Barrier Reef was hardest hit during the more recent event, but the greatest global effect was observed in 1998, which left an estimated 16 per cent of the world's coral reefs catastrophically damaged. Corals and anemones are acclimatised to the environment in which they are found, so any rise in sea temperature would threaten the inhabitants of that environment.
The response of coral reefs to an increase in water temperature depends on the adaptive ability of their resident zooxanthellae. AG Society sponsored PhD student Laura Wicks, from the Victoria University of Wellington, NZ, has recently examined the diversity of zooxanthellae found in corals at Lord Howe. She has determined that the diversity here is of particular significance with respect to global climate change, because different types of zooxanthellae exhibit striking differences in their susceptibility to temperature increases. According to Laura: "The diversity of zooxanthellae is high at Lord Howe Island, which means there may be species that can tolerate greater temperature variation, resulting in anemones and corals that are more resilient to changes in temperature."
Ball's Pyramid, near Lord Howe the world's tallest sea stack
Balls Pyramid, an imposing 551 m rocky spike 23 km south-east of Lord Howe, is the tallest sea stack in the world. But for many, the towering rock's true majesty is below sea level - in its teeming population of kaleidoscopic marine life, including the captivating Ballina angelfish.
We've decided to extend our survey to the waters surrounding the pyramid and I make the trip out with Brian 'Busty' Busteed, a particular fan of the angelfish. The enigmatic fish was first described in 1959 by Gilbert Whitley, based on a single specimen collected off the coast of Ballina, far northern NSW, and has only been seen on a couple of occasions since then, including one by Brian, at Balls Pyramid in 1999. A pod of dolphins accompanies us as we motor towards the remote stack, which appears to double in size with every passing minute until we reach its base. Staring up at the peak, I'm struck by its grandeur.
With tanks on our backs and regulators in our mouths we slip into the drink. We're engulfed by schools of bluefish and drummer in water so clear that shafts of sunlight pierce the surface like laser beams, spotlighting the seabed 20 m below. As the current pushes us along a vertical reef wall we come across an amazing coral garden filled with treasures. A delicate Spanish dancer nudibranch is laying a pink shawl of eggs and a pair of hermit crabs squabble over territory. Suddenly, from the corner of my eye, I catch a flash of pearl, black and yellow. Holding my breath so as not to 'bubble', I crawl along the boulder-strewn sea floor and come face to face with a striking pair of 20 cm long Ballina angelfish. I admire them for a few fleeting moments before they dart away.
Over the coming days we complete our surveys, at 23 sites in total, and there's a sense of relief. The prognosis is good; Lord Howe's lagoon has some of the world's highest densities of anemonefish and the McCulloch's anemonefish seems safe for now. And thanks to the establishment of the community-based monitoring program, the locals will keep a keen eye on their precious marine milieu, which teems with life both rich and rare.
Living large on Lord Howe Island
Secret life of green turtles on Lord Howe Island
First video: Australian deep sea canyon
10-year maring census finds thousands of new species
Sea creatures set sail on rafts of kelp
GALLERY: reef and rainforest
Ningaloo Reef revealed
Fearsome giant turtles found in Pacific cemetery
Island nation: Australia's 8222 islands
In pictures: the secret life of green turtles
Source: Australian Geographic, Issue 96 (Oct - Dec, 2009)