struck again by the extraordinary stars and the lightless horizon. I also
felt, as I had several times at One Tree, the incongruity of my position.
The reason I’d come to the Great Barrier Reef was to write about the scale
of human influence. And yet Schneider and I seemed very, very small in
the unbroken dark.
LIKE the Jews, the corals of the Great Barrier Reef observe a lunar
calendar. Once a year, after a full moon at the start of the austral summer,
they engage in what’s known as mass spawning—a kind of synchronized
group sex. I was told that the mass spawning was a spectacle not to be
missed, and so I planned my trip to Australia accordingly.
For the most part, corals are extremely chaste; they reproduce
asexually, by “budding.” The annual spawning is thus a rare opportunity
to, genetically speaking, mix things up. Most spawners are
hermaphrodites, meaning that a single polyp produces both eggs and
sperm, all wrapped together in a convenient little bundle. No one knows
exactly how corals synchronize their spawning, but they are believed to
respond to both light and temperature.
In the buildup to the big night—the mass spawning always occurs
after sundown—the corals begin to “set,” which might be thought of as
the scleractinian version of going into labor. The egg-sperm bundles start
to bulge out from the polyps, and the whole colony develops what looks
like goose bumps. Back on Heron Island, some Australian researchers had
set up an elaborate nursery so they could study the event. They had
gathered up colonies of some of the most common species on the reef,
including Acropora millepora, which, as one of the scientists put it to me,
functions as the “lab rat” of the coral world, and were raising them in
tanks. Acropora millepora produces a colony that looks like a cluster of tiny
Christmas trees. No one was allowed to go near the tanks with a flashlight,
for fear that it would upset the corals’ internal clocks. Instead everyone
was wearing special red headlamps. With a borrowed headlamp, I could
see the egg-sperm bundles straining against the polyps’ transparent