Coral reefs are dying around the world. A report released by the Global Coral Reef Monitoring Network in 2004 found that more than 2/3 of the world's coral reefs are on the verge of collapse… or already destroyed.
The coral reefs in Hawaii are still pristine, which is why after a large tanker ran aground earlier this year off the coast of the island of Oahu, a major effort was launched to repair the damage done by the ship and its anchor to the delicate coral reef growing in the offshore waters.
The unusual repairs were accomplished by teams of divers hauling buckets of special cement 20 meters down to the ocean floor.
The 170-meter long Cape Flattery was carrying a load of powdered cement when the Hong Kong-registered vessel struck the reef off the Hawaiian island of Oahu. While some cement spilled and hardened during the emergency off-loading, much of the damage to the reef came from the ship's anchor and tugboat cables.
John Naughton, a biologist with the National Oceanic and Atmospheric Administration, says emergency repair work began at once. "We were astounded by all this coral that had been toppled," he says. "We suddenly realized that we have got to stabilize as much of this as possible, because the individual corals heads would die, because they would be moved around. The second thing is that they (corals) act as large bowling balls on the bottom and in the first storm (they would) go careening into the remaining coral and do a lot more damage."
Mr. Naughton and his colleagues came up with the idea to cement the damaged corals back in place. Divers adapted a technique normally used in shallower water. One hurdle was to get the pre-mixed compound to a depth of 20 meters before it hardened. "We have had to devise ways with these 5-gallon (19 liter) buckets to cap them," he says. "You (have) to let water in, so you didn't get pressure gradient differentials. When you are working in shallow water, you don't have to worry about SCUBA, decompression -- a whole lot of different things that you have to worry about (in deeper water).
Nearly every day for 2 months, divers worked like underwater bricklayers transplanting and reattaching broken coral. "Some of the coral was sheered off. So the base of the coral was still there," Mr. Naughton says. "Those corals we feel will come back as long as they are stabilized and not moving around. The tissue will grow over the damaged ends where they were sheered off. So we left those alone. But we gathered up the big branches that were broken off in some cases and those we stuck around into clusters, and those seem to be fine too. So it was very encouraging."
Coral doesn't die when it breaks. "Corals are just a sheath of living tissue - living cells or polyps - around the older coral skeleton," Mr. Naughton says. "As they grow there is of course dead material inside, but that is what forms the reef." What kills the coral polyps, he says, is abrasion against the bottom of the ocean. "That is why stabilization is so important. This way we were able to stabilize and we were able to do the actual restoration work." And, Mr. Naughton says, they have been pleased with results: "The bottom, the cement pads themselves, are totally non-toxic, and we see natural colonization of algae and new coral settling on it. It sort of replicates the normal limestone bottom."
The repairs appear to have saved the reef in the short term. NOAA plans to continue monitoring conditions over time. A failure of the reef to hold up would result in a critical loss of biodiversity and shore protection, problems that threaten reefs around the world.
