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Page 1 | Page 2 | Page 3 | Page 4 The Inverted PyramidEureka! We found it. A pristine reef where corals
are alive and healthy and form a forest so thick that there is no space
even for sand between them. A reef where sharks are not used to seeing
humans and, instead of swimming away, they come by the dozens and swim
around you during the entire dive. A reef where one's heartbeat doubles
as soon as we disappear below the surface. This is Kingman Reef, the
pearl of the Line Islands. The classically accepted picture of a marine community takes the shape of a pyramid, in which a small number of large predators sit at the top, a larger number of plant-eating fish and invertebrates lie in the middle, and a very large abundance of plants and algae form the base. A comparative examination of two of the Line Islands, however, is telling a much different story. Off the heavily populated and highly fished waters of Kiritimati, or Christmas Island, the researchers observed a classic food chain pyramid. But when they arrived at the virtually pristine waters of Kingman Reef, they found the pyramid was turned on its head. They found a large number of predatory sharks, snappers, and groupers at the top of the food chain, a much sparser population of fish in the middle and a drastically smaller algal population at the base. 
Enric Sala, a marine ecologist and adjunct professor at Scripps, was shocked when he dived there for the first time. He uses an analogy based in the African Serengeti to properly frame the experience: "It was like seeing five pounds of lion for every pound of wildebeest or zebra," said Sala, the expedition leader. This led to the question: What makes a food pyramid go upside down in an undisturbed environment? Sala believes the answer is not easily derived, mainly because, as marine ecologists have come to realize in recent years, coral reef ecosystems encompass thousands and thousands of connections that make up the pyramid. Multitudes of animals, plants, and bacteria all have a role to play. Rather than a linear chain, in reality it's an intricate food web. 
One explanation for the inverted pyramid focuses on the importance of sharks in coral reef ecosystems, a function still poorly understood by scientists. "The coral reef food web is not static," said Sala. "It's like a house made out of matches, but the matches are continuously changing places. Then we have the threats of pollution, global warming, and overfishing. I believe sharks are the very foundation for the stability of the house." Next Page: 'Every ecosystem has lost its predators' |
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