Tuesday, September 22, 2009

Three-part Day: Green Island, Blue Desert, Reef Oasis

Kate Madin, Woods Hole Oceanographic Institution
Today we are at Orona Island, a large atoll lush with coconut palms and other greenery. It was a busy day, with blue water and reef dives, plus a shore visit to an abandoned village.

People from Kiribati have occupied Orona three times, said Tukabu — most recently by islanders harvesting copra (coconut meat) and fishing, until about 2003. Several scientists and crew on Nai’a have fond memories of dancing and feasting with the villagers, when visiting here during the 2002 expedition to the Phoenix Islands. But the people left when the village couldn’t sustain itself any longer. Buildings being reclaimed by jungle, paths disappearing, and the island is left to land crabs, birds, and jungle. We also saw low stone walls that Tukabu said were built by Polynesian settlers, hundreds of years ago, who also did not stay.

Randi Rotjan and Jim Stringer joined Larry and me on a blue water dive this morning. The dive was eventful because a 6-ft. shark came around and looked us over a couple of times, but the large plankton animals were very sparse. Some salps – the transparent 2-inch animals Larry is interested in – drifted by us in the blue expanse, but we didn’t see much else in the upper ocean waters.

“Dives in the surface water of the tropical ocean are very different from some dives I’ve made in the North Atlantic,” Larry said, “where sometimes we’ve seen salps and jellyfish in swarms of thousands. The reason is that the ocean here has only low levels of the nutrients that plankton need, such as nitrogen. Without it, phytoplankton (microscopic plants) can’t grow, and there’s little food for bigger plankton. It’s almost an ocean ‘desert’.”

If the blue water seems like a desert, the reefs are an oasis, but a damaged one. Orona’s reefs, like at all the islands, are mixed – some are healthy, and some are recovering slowly after the bleaching in 2002. But many kinds of fish thrive here still, especially the ones that feed on algae that grows over dead coral.

In the late afternoon, Greg put the small ROV (remotely operated vehicle) into the water right near the boat, to have a look at the deeper water, too deep for scuba divers. The coral extends down to the bottom, nearly 200 feet down. The water here is so clear that sunlight penetrates that far, allowing the corals to grow.

Watching the video transmitted by the ROV, Les Kaufman identified fish near the bottom, calling out “white tailed surgeon fish”, “yellow bellied snapper”, “goatfish”… and a school of “unicorn surgeon fish” – fish that eat the salps that drift in over the reef from blue water –one more sign of how connected are the reefs to the open ocean.

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