National Geographic : 2017 Jun
Some of Darwin’s finches lie arranged around an assortment of local seeds at the Charles Darwin Research Station on Isla Santa Cruz. Climatic extremes are the norm in the Galápagos. Birds that thrive here have beaks whose size, width, and shape have adapted to exploit the seeds available for them to eat. communities that live on and around the sea floor—sponges, corals, barnacles, fish—inter act. The Galápagos have some of the planet’s healthiest tropical marine systems. The coral communities are thickets of biodiversity. “It’s like a bush on land,” Witman says, but instead of birds, the corals harbor symbiotic crabs and snails, as well as fish. One reason the Galápagos are unique and so diverse—the reason, for instance, that penguins can share a beach with flamingos—is that four main ocean currents of varying temperatures bathe the islands. The deep, cold Equatorial Undercurrent, which travels about 8,000 miles across the Pacific, slams into the islands, upwells, and swirls around them, bringing to the surface nutrients that fertilize phytoplankton. This in turn fuels the rest of the marine food web. Ev erything is built upon this conveyor belt. During El Niño the trade winds slacken. This weakens the upwelling of cold water and nutrients from the deep and also causes the pool of warm water in the western Pacific to expand toward the Galápagos. The conveyor belt nearly shuts down. The buffet closes. Marine life suffers dramatically. Some creatures may stop breeding; some even starve. Some populations still haven’t recovered from an extreme 198283 El Niño. The Galápagos damselfish is now believed to have gone extinct because of that event. Meanwhile, fortunes are of ten flipped on land, where El Niño usually brings drenching, lifegiving rains to the desert isles. La Niña overturns everything. Marine life prospers while terrestrial life languishes. Wit man likens the natural, repeated cycle to a roller coaster: Deprivation. Recovery. Abundance. Re peat. During Witman’s watch the Galápagos have experienced three major El Niños. In 2016 the warm waters led to reduced amounts of the algae the larger marine iguanas forage for in the sea. Witman’s question is this: If waters here are PHOTOGRAPHIC FIELDWORK WAS FUNDED IN PART BY THE SAVE OUR SEAS FOUNDATION, THE PAUL M. ANGELL FAMILY FOUNDATION, AND FON (FOCUSED ON NATURE).