reef-building corals lead double lives. Each individual polyp is an animal
and, at the same time, a host for microscopic plants known as
zooxanthellae. The zooxanthellae produce carbohydrates, via
photosynthesis, and the polyps harvest these carbohydrates, much as
farmers harvest corn. Once water temperatures rise past a certain point—
that temperature varies by location and also by species—the symbiotic
relation between the corals and their tenants breaks down. The
zooxanthellae begin to produce dangerous concentrations of oxygen
radicals, and the polyps respond, desperately and often self-defeatingly,
by expelling them. Without the zooxanthellae, which are the source of
their fantastic colors, the corals appear to turn white—this is the
phenomenon that’s become known as “coral bleaching.” Bleached
colonies stop growing and, if the damage is severe enough, die. There
were major bleaching events in 1998, 2005, and 2010, and the frequency
and intensity of such events are expected to increase as global
temperatures climb. A study of more than eight hundred reef-building
coral species, published in Science in 2008, found a third of them to be in
danger of extinction, largely as a result of rising ocean temperatures. This
has made stony corals one of the most endangered groups on the planet:
the proportion of coral species ranked as “threatened,” the study noted,
exceeds “that of most terrestrial animal groups apart from amphibians.”
ISLANDS are worlds in miniature or, as the writer David Quammen
observed, “almost a caricature of nature’s full complexity.” By this
account, One Tree is a caricature of a caricature. The whole place is less
than 750 feet long and 500 feet wide, yet hundreds of scientists have
worked there, drawn to it, in many cases, by its very diminutiveness. In
the nineteen-seventies, a trio of Australian scientists-set about producing
a complete biological census of the island. They spent the better part of
three years living in tents and cataloging every single plant and animal
species they could find, including: trees (3 species), grasses (4 species),
birds (29 species), flies (90 species) and mites (102 species). The island,