In Darwin's Wake

Handholds and Hammerheads
The iguanas, blue-footed boobies, penguins, seals, and frigate birds are what most visitors long to see in the wild during their time in the Galápagos. To do so, one must still enlist the services of a licensed guide. While several of the crew booked sanctioned trips to other islands for hikes and terrestrial tours, photographer David Thoreson and I chose to see what was happening below sea level.

Swallowtail gull

The Galápagos have become one of the planet’s premier diving destinations because without fail, once you’re in the water, you’re guaranteed the opportunity to interact with big animals: surprisingly graceful sea turtles, playful sea lions, and majestic rays, including mantas, that fly beneath the seas. Then there are fish: grunts and wrasses and snappers and idols and grouper and barracuda and parrotfish and on and on, of every size, color, and description.

Finally, there are sharks: white- and black-tipped reef sharks. Galápagos sharks. Hammerheads. On our first day of diving—initially to a location called Isla Beagle, on the southern flank of Isla Santiago, which is also known as Isla San Salvador, and then to a low, sandy island called Isla Mosquera, just north of Isla Baltra—we saw them all.

We also saw plenty of coral, in a variety of species, including prominent coral heads, intricate expanses of coral reefs, undulating sea fans, and big, oval sculptures of brain coral. Almost always, reef fish or sharks swam nearby, in various stages or acts of feeding or cleaning. It was a vivid, industrious, colorful, and vital panorama.

From oceanographer Banks, we’d learned that the coral we viewed was susceptible to changing climates and to El Niño events.

“When we get a strong El Niño, it can drastically change the entire marine ecosystem,” he said. “We’ve seen that already. We know that Galápagos corals are some of the most sensitive groups to climate change, and in the very intense 1982-1983 El Niño, the Galápagos lost about 97 percent of its reef-forming corals in a year and a half. They were bleached through hot-water stress, in which algae that forms in the corals is naturally expelled. It can always reintegrate back into the skeleton if conditions change, and the coral can recover. But when that stress is sustained for long periods, it’s not possible. Then the coral starts to die.”

The broader problem, of course, is that coral reefs are building blocks, even frameworks, for entire undersea communities. Banks said, “A whole host of other species—sea urchins, sea cucumbers, sea stars, reef fish—are all interactive and interdependent on this coral resource. So within about a year, the entire character of the ecosystem in Galápagos changed, because these are habitat-forming species, species that are particularly important in nursery areas. They give shelter and protection, but they also give kind of a three-dimensional complexity and structure in which other species can co-exist.”

Acts of nature were only one part of the potential problem. People, naturally, were the other. Overfishing can also topple the delicate balance in reef life. When lobsters and other reef fish were taken off the reef in abundance, the sea-urchin population skyrocketed. “The sea-urchin explosion infiltrated the reef structure and started breaking apart these reefs from the inside,” said Banks.