The Sixth Extinction: An Unnatural History

Some of the scientists, who had dived all over—in the Philippines, in
Indonesia, in the Caribbean, and in the South Pacific—told me that the
snorkeling at One Tree was about as good as it gets. I found this easy to
believe. The first time I jumped off the boat and looked down at the swirl
of life beneath me, it felt unreal, as if I’d swum into the undersea world of
Jacques Cousteau. Schools of small fish were followed by schools of larger
fish, which were followed by sharks. Huge rays glided by, trailed by turtles
the size of bathtubs. I tried to keep a mental list of what I’d seen, but it
was like trying to catalog a dream. After each outing, I spent hours
looking through a huge volume called The Fishes of the Great Barrier Reef
and the Coral Sea. Among the fish that I think I may have spotted were:
tiger sharks, lemon sharks, gray reef sharks, blue-spine unicorn fish,
yellow boxfish, spotted boxfish, conspicuous angelfish, Barrier Reef
anemonefish, Barrier Reef chromis, minifin parrotfish, Pacific longnose
parrotfish, somber sweetlips, fourspot herring, yellowfin tuna, common
dolphinfish, deceiver fangblenny, yellow spotted sawtail, barred
rabbitfish, blunt-headed wrasse, and striped cleaner wrasse.
Reefs are often compared to rainforests, and in terms of the sheer
variety of life, the comparison is apt. Choose just about any group you
like, and the numbers are staggering. An Australian researcher once
broke apart a volleyball-sized chunk of coral and found, living inside of it,
more than fourteen hundred polychaete worms belonging to 103 different
species. More recently, American researchers cracked open chunks of
corals to look for crustaceans; in a square meter’s worth collected near
Heron Island, they found representatives of more than a hundred species,
and in a similar-sized sample, collected at the northern tip of the Great
Barrier Reef, they found representatives of more than a hundred and
twenty. It is estimated that at least half a million and possibly as many as
nine million species spend as least part of their lives on coral reefs.
This diversity is all the more astonishing in light of the underlying
conditions. Tropical waters tend to be low in nutrients, like nitrogen and
phosphorus, which are crucial to most forms of life. (This has to do with