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The coral reefs of Bora Bora
Bora Bora, Society Islands, French Polynesia – I dove in the beautiful lagoon that surrounds the tall island to have a first hand look at how the coral reef is doing in this South Pacific resort island. The report is not good.
Descending to ninety feet it was immediately clear that the reef has been hammered in the past few years. I've come here every year for the past decade and have seen incredible change.
I spent most of the morning observing the still-growing reef system just ten to thirty feet below the surface. Although the waters are warm and magnificently clear an invasive predators and natural disaster have both taken big tolls.
Populations of acanthaster -- more popularly known as the Crown of Thorns starfish – mysteriously arrived in Polynesia in 2006. No one is sure exactly how they got here or where they originated, though invasive species are well known for hitching rides on cargo ships and jumping off far from home. Here in the shallows surrounding Bora Bora – as they have done to reefs on nearby Moorea, Raiatea-Tahaa, Huahine and Maupiti – the predatory starfish have eaten, thus killed, hundreds of acres of coral.
The natural disaster occurred in February 2010, when Cyclone Oli whipped the nearby seas to a froth of eighteen to twenty-one feet, pouring over the protective reef and across the lagoon. The impact on the corals was devastating, as deep as 100 feet below the surface.
At twenty feet below, the coral was ripped off at its base and forever destroyed. Rather than coral, today much of the shallows of the lagoon floor are covered instead of by a fine pale yellow algae mat. The deeper you dive, the less destruction you see, but the powerful storm – the first cyclone to hit here in fourteen years -- still managed to break, mangle and kill coral. The only slight upside is that it was also hard on the starfish population.
Around the globe more than 275 million people live in the direct vicinity (within 18 miles) of coral reefs. In more than 100 countries and territories reefs protect over 93,000 miles of shoreline, helping defend coastal communities and infrastructure against storms and erosion.
The reef encircling Bora Bora helps protect the island from typical weather and seas. Human pressure on the reef and lagoon come from development: Thirteen big hotels are built either on the mainland or one of its several big motus. In the past decade the human population has swelled to 9,000, thanks to tourism. But the twin pressures of more building and more people is having a direct impact on the very thing – its amazing natural beauty – that attracts visitors in the first place.
My morning dive led me to a conversation in the late afternoon with French-German marine biologist Denis Schneider. Despite his mainland birth, Schneider has been an island-rat most of his adult life. He guesses he spend 30 hours a week – five hours a day, six days a week – in the ocean. He only occasionally wears shoes. His company – Espcae Bleu – works to rebuild reefs in Indonesia, the Maldives and Bora Bora.
"The three biggest problems for the reef here – before the starfish arrived – were people, especially fishermen and their motors, the Red tide which warms the water and kills the coral, and hurricanes." He and his team have taken on the unenviable attempt to clear out the venomous starfish. "Touch a sea urchin and the sting will last for a few minutes," he says. "Brush your skin against a Crown of Thorns and it will sting for months." The solution to ridding the lagoon of the starfish is injecting them one by one, using giant hypodermic needles, with a chemical solution that kills them. (He changes the subject when I ask what impact the chemicals may have on the lagoon ....)
To try and resuscitate reefs, especially near the hotels, Schneider and compatriots from the Maryland-based Global Coral Reef Alliance, build unique domes out of rebar which they flip over and sink to the lagoon floor. The metal rusts very quickly and the chicken-wire mesh covering it is soon grown over by calcium-rich marine life. Coral is transplanted onto the faux reef and within a year it is nearly completely covered with colorful, living coral. They've dubbed the patented system Biorock and its trick to growing coral on the super-structure fast is that the underwater structure is "electrified." To encourage fast-growing coral a low voltage current courses through the metal structure, usually created from solar, wind or tidal sources. .
"What we are building are really 'boosters' for the reefs, growing three to five times faster than normal coral," says Schneider. "In some cases 20 times faster. "
The Biorock system is just one of a variety of man-made attempts being made around the world to encourage new coral growth, including concrete forms and, around the coast of the U.S., purposely dumped buses, tanks and aging military boats.
"The reality in Bora Bora is that the island, like all in Polynesia, is sinking. Slowly, very slowly. But in 70,000 years the island will be gone and all that will remain will be the reef surrounding the lagoon. I wish we could come back then and see how the coral has done."
[flickr image via Jon Rawlinson]