Darwin’s Creatures Are at Risk From Warming Seas
their recent past, when one such event bore down on these islands. Warm El Niño waters blocked the rise of nutrients to the surface of the ocean, which caused widespread starvation.
Large marine iguanas died, while others shrank their skeletons to survive. Seabirds stopped laying eggs. Forests of a giant daisy tree were flattened by storms and thorny invasive bushes took over their territory. Eight of every 10 penguins died and nearly all sea lion pups perished. A fish the length of a pencil, the Galápagos damsel, was never seen again.
That was in 1982. The world’s oceans have warmed at least half a degree Celsius since then.
David J. Anderson, a biologist at Wake Forest University in North Carolina who studies the blue-footed booby, a seabird, said the ravages of El Niño were a surprise when he began working on the islands in the 1980s.
“Now we are wondering, how frequent do these things get? El Niños have a bulldozer effect,” he said. “And they are happening more and more.”
Though the Galápagos lie at the heart of the geographic tropics, it’s hard to guess that, standing on one of the islands, because of a vast current that flows north from southern Chile. That stream, the Humboldt Current, keeps the islands cool and rainless, unusual given that the Equator crosses through the archipelago. It means the islands are subtropical in climate, a rare place where penguins and corals exist side by side.
But sometimes the cool Humboldt Current suddenly slows.
The ocean waters start warming rapidly, heating up as much as 2 degrees Celsius within months. Storms begin to strike the islands. And, as if overnight, the Galápagos become warmer: It is the start of El Niño. “The Galápagos marine system is analogous to a roller coaster,” said Jon D. Witman, a professor at Brown University in Rhode Island who studies coral ecosystems in the Galápagos, noting that the spikes of hot temperatures were followed by falling temperatures, known as La Niña.
The problem with global warming, Dr. Witman said, is that the baseline from which these swings occur is rising as the ocean temperatures do. This, as the intensity and frequency of El Niño is increasing.
Before he published “Moby Dick,” Herman Melville sailed past the Galápagos and saw the black marine iguanas on the rocks. They were “that strangest anomaly of outland- ish nature,” he wrote in the 1850s.
One particular anomaly of the marine iguanas offers a clue into what warmer Galápagos seas may be facing.
Martin Wikelski, a biologist at the Max Planck Institute of Ornithology in Germany, was spending his research seasons off the coast of Genovesa Island when he noticed something strange in his calculations. When the seas warmed, the size of the iguanas decreased.
“Obviously an animal can’t shrink, it’s impossible,” he said he initially thought. “But they looked odd, like frogs where the legs were too long for the body.”
The iguanas were in fact becoming much smaller.
Rising ocean temperatures mean less algae, the main source of food for marine iguanas. Scientists say they believe that the reptiles may reabsorb parts of their skeleton to decrease their size and increase their chances of survival on a smaller diet. Stress hormones may trigger the process, but little more is understood. Nevertheless, the changes could be central to their survival as El Niño cycles become more frequent.
Evolution has led other animals in different directions, which could now prove fatal as ocean temperatures rise.
One day on Isabela, the largest island in the Galápagos, a male sea lion howled over a gaggle of pups in a tide pool. Sea lions and fur seals here have no set breeding season, so males are constantly on the defense against competitors — a costly vigilance that takes away from their time to hunt fish.
When sea temperatures rise, the sardine population here drops. In the 1982 El Niño, nearly every large adult male fur seal died of starvation. Most of the sea lion pups born that year died as well because parents couldn’t feed their young, according to a study by Fritz Trillmich, an ecologist.
“It’s like if our generation didn’t have kids,” said Robert Lamb, a doctoral candidate at Brown University.
Creatures have also been devising new ways to hunt.
In November, the craggy rocks in a cove off the shore of Isabela Island were strewn with the bones of a massive fish — a tuna, which scientists say they haven’t seen sea lions eat before. But just after dawn on a recent morning there, sea lions chased one large tuna into the cove, then slaughtered it in the shallows.
Whether this is simply a new behavior that emerged when populations of smaller fish grew scarce hasn’t been studied, but the new diet could prove advantageous to sea lions as El Niños become more frequent.
Other animals have fewer options to change their diet.
Blue-footed boobies, birds known for their bright feet and clownish waddle, line the shores here. But at sea, these specialized fish- eaters soar gracefully above the waves before plunging into the ocean like competitive divers, scattering the clouds of fish so they can be picked off individually.
The blue-footed boobies once lived on sardines. But sardine populations plummeted in 1997 and the fish remain scarce, forcing the birds to eat other fish. When sea temperatures rise during El Niño, these other fish also start to disappear.
“They basically stop trying to breed,” Dr. Anderson said of the boobies. He said the pattern had become more frequent in parallel with El Niños.
“One hundred years from now, I would not be surprised if the blue- footed boobies were gone” if current trends continue, Dr. Anderson said.
Similar behaviors are seen in other aquatic birds here. Galápagos penguins, which are only found on these islands, stop breeding when the water reaches 25 degrees Celsius.
Flightless cormorants starve at their nests because they cannot travel to find food elsewhere when fish populations drop near the islands.
While warmer temperatures often spell doom for native species that evolved to the Galápagos’ cool subtropical climate, invasive species flourish.
Forests of the Scalesia, a giant daisy tree that is unique to the Galápagos, were already shrinking because of clear- cutting for agriculture in the highlands. The trees are accustomed to mild weather, so the violent storms that come with extreme El Niños can flatten their forests. While destructive, storms have long been part of a natural cycle for these daisy trees, allowing a new generation to take root after the last.
With climate change, however, the process is being short- circuited. Below the Scalesia forests, the seeds of an invasive blackberry wait for the giant daisy trees to fall. The blackberry plants quickly spread, blocking the next generation of the trees.
Another invasive species that worries scientists is the fire ant, which flourishes in wetter climate and eats the eggs of giant tortoises.
Workers at the Galápagos National Park are now considering mitigation efforts to try to protect threatened species from the more frequent El Niño events that have come with climate change. The park already has a program to breed giant tortoises in captivity.
But not all giant tortoises can be bred in a pen.
Nor can many of the other creatures on these islands.