Yellow and blue fusiliers shoal over a reef in the Chagos Archipelago. Thanks, poop.
Photo: Nick Graham

Bird turds can tell you a lot about an island. For instance, is it smelly or not? But also, how are the coral reefs doing?

Research published on Wednesday in Nature shows that at least for one archipelago, the shittier the island the healthier the reefs and fish around them. That insight is crucial for conservationists looking to give reefs a little help in troubling times.

So, here’s the thing about poop. It’s fertilizer, containing nitrogen and other nutrients that can help things grow. Scientists have known that seabird poop can be an important source of nutrients for coral reefs, but they haven’t been able to get a handle on just what happens when you have less shit to go around because, well, you can’t just go wipe out a colony of birds and see what happens to the reefs living nearby.

But the Chagos Islands, a remote archipelago of atolls in the Indian Ocean, offered an international team of researchers a unique opportunity. The northern end of the archipelago has been uninhabited by humans for 40 years, but seafarers left behind colonies of black rats on some of the islands. Those rats have occupied the islands since the 18th century, and with no natural predators, they’ve been able to multiply and feast on young seabirds and eggs.

That allowed the researchers to look at the state of bird poop on islands with rats and islands without them. The results are astonishing.

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Seabird densities were 760 times higher on rat-free islands and nitrogen deposits were 251 times higher. All the sweet, glorious bird poop-derived nitrogen provided a huge boost to the surrounding reefs, which had 48 percent more biomass and larger, healthier fish. Healthy herbivorous fish grazed reefs nine times each year near the rat-free islands vs. only 2.8 times annually on the rat-infested ones. And bio-erosion—a process that breaks down dead coral so new coral can thrive—was more common in rat-free zones.

Good job, poop.

“This important new study clearly shows how all components of natural ecosystems are connected, and underscores how important it is that we conserve all the major players in our ocean ecosystems,” Julia Baum, a coral reef researcher at the University of Victoria, told Earther.

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This is feel good news in a sea of terribleness surrounding coral reefs. Rising ocean temperatures have battered reefs around the world, including permanently altering the Great Barrier Reef. As the ocean keeps warming, reefs will face increasingly hostile conditions and even extinction.

Of course, these results are just from one set of islands, and more research is needed to see if they translate elsewhere. But seabird poo is an important source of nutrients in other ecosystems. Anne Guerry, the lead scientist at Stanford’s Natural Capital Project, told Earther the study highlights why research on indirect impacts of invasives is so important elsewhere, and that it “helps to bump up the importance of conservation and restoration activities that target the eradication [of] high-impact non-native species.”

And while bird poop alone won’t save reefs from the heat, the new research does show that conservation strategies on land can pay dividends in the sea. The Chagos Conservation Trust, a local group working on the islands, completed its first successful rat eradication last year. Other efforts are afoot to wipe out invasive rats on other islands around the globe. Some research indicates that it only takes seabirds a few decades to recover once the rats are gone. That in turn, may pay dividends to the reefs and sea creatures that call them home.

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It’s all connected yo.