Scientists Look to Seabird Recovery to Protect Coral Reefs

On some islands, the partnership between birds and reefs has broken down. Seabird colonies have declined because of habitat loss and invasive species such as rats. With fewer birds, fewer nutrients reach the ocean. Coral restoration projects are now also focusing on bringing back seabird colonies, reestablishing a link that helps both species. Coral reefs are increasingly vulnerable to rising ocean temperatures, and biologists say they need every advantage in a hotter world.

"If we can figure out ways to just stop the local threats to ecosystems, they will, in a lot of cases, find ways to repair themselves," said Alex Wegmann, lead scientist for The Nature Conservancy's island resilience strategy. "They can reestablish their natural functions that will then allow them to adapt to the climate impacts that are coming."

More than a thousand miles south of Hawaii, Palmyra Atoll offers a window into how the system works. In its rainforest, a white tern chick the size of a fuzzy, white golf ball perches on a tree limb while its parents hover nearby, chattering rhythmically. Paige Mino, manager of the Palmyra Atoll National Wildlife Refuge with the U.S. Fish and Wildlife Service, described the chick as young. "I think that their call sounds like an electric rubber band snapping," she said.

The forest echoes with the calls of seabirds, including red-footed boobies, large birds with bright blue beaks and red feet. Almost all of the birds on Palmyra Atoll rely on the ocean, flying out to sea daily to feed on fish or squid and bringing some back for their young. The abundance is due in large part to the atoll's remote location. Polynesians likely visited Palmyra on seafaring voyages, but the atoll was not permanently inhabited. In the 1800s, coconut plantations were developed. During World War II, the U.S. military turned the atoll into a logistical station, building bunkers and roads. In 2000, The Nature Conservancy bought Palmyra Atoll from private owners and transferred the majority of it to the federal government. The U.S. Fish and Wildlife Service manages it as a national wildlife refuge.

"There's no human impact of pollution or overcapacity, so I think it really gives the wildlife and vegetation the space to thrive," Mino said. "It gives the wildlife a chance to do what they naturally do."

Palmyra's thriving ecosystem has helped scientists uncover a nutrient recycling system that starts with the birds. When seabirds return to land after eating fish at sea, they roost in trees and deposit nutrients in their guano. One study of almost 200 atolls estimated that seabirds brought more than 100,000 pounds of nitrogen back to land. That acts as a fertilizer, nourishing trees and plants. Frequent heavy rains then wash the nutrients into the ocean, where they help the marine food web. Tiny microscopic plankton grow, feeding larger plankton that are eaten by many species, including fish and manta rays. Corals also eat plankton, though it is not their primary food source.

"Studies show that those marine nutrients from seabird guano are really valuable and important for the whole reef ecosystem," said Katie Franklin, who works on Palmyra Atoll conservation strategy for The Nature Conservancy. "Guano will help nourish the ecosystem from the rainforest to the reef, so we really just want to bring on more guano."

Scientists noticed more than a decade ago that manta rays were more commonly seen in waters near seabird colonies. The massive mantas, some with a 9-foot wingspan, slowly glide through the water as they feed on tiny plankton. Some forests on Palmyra Atoll are eerily quiet, and birds are hard to find in them.