The Big Picture: Why Nutrient Pathways Matter

Coral reefs thrive on nutrients, but in many tropical island ecosystems, those nutrients don’t just come from the ocean. They also come from seabirds—which aren’t just keystone species, but connector species. These birds feed far out at sea and return to islands to nest, depositing guano (or poop) rich in nitrogen and phosphorus. These nutrients wash into coastal waters, fueling algae and coral growth and supporting vibrant reef communities.  

When harmful invasive species like rats were introduced to islands centuries ago, they devastated seabird populations. Fewer seabirds mean less guano—and a critical nutrient link between land and sea gets severed.  

But there’s hope. We know that islands can recover incredibly quickly when invasive species are removed. For example, on Palmyra Atoll in the Pacific, our team removed invasive rats and found that the returned seabirds enriched the soil and boosted native plant growth by 5,000%. When we bring back connector species, all parts of an ecosystem flourish. 

Active vs. Passive Nutrient Transfer 

The study distinguishes two pathways: 

• Passive nutrient transfer: Nutrients delivered by ocean currents and upwelling. 

• Active nutrient transfer: Nutrients delivered by animals—like seabirds—moving between ecosystems. 

Healthy reefs need both. But when seabirds disappear, active transfer collapses. This is especially critical for delicate corals, which rely on nitrogen-rich waters to grow and recover from stress. Without seabird-derived nutrients, these corals grow more slowly and are less resilient to bleaching events. 

What the Study Found 

Researchers modeled what would happen if invasive predators were removed and islands restored. The results are stunning: 

• Seabird populations could rebound to over 280,000 breeding pairs across Chagos. 

• Their guano would dramatically increase nitrogen input to coastal waters. 

• Coral growth rates, reef fish biomass, and parrotfish grazing—all essential for reef health—would rise significantly. 

In fact, corals near islands restored in this way grow 4x faster and recover more quickly after bleaching, thanks to the nutrient boost from seabird guano. 

To trace nutrient flows, scientists used stable isotope analysis, a technique that measures chemical signatures (like nitrogen isotopes) in plants and animals. Higher nitrogen isotope values near seabird islands confirmed that guano enriches reef ecosystems. 

Why Does it Matter? 

Coral reefs are frontline defenders against climate change, protecting coasts and supporting fisheries. But they’re under siege from warming seas, extreme weather, and bleaching events. Rebuilding seabird populations through holistic island restoration offers a natural, scalable way to strengthen reef resilience. By reconnecting nutrient pathways, we help corals grow faster, recover from bleaching, and withstand climate stress, giving them a fighting chance in a warming world. 

And people benefit, too: thriving reefs protect coastal communities from storm surges, slowing down erosion. The fish that live in reefs—which can increase in biomass when nearby islands are restored—feed island communities. And eco-tourism, which booms where reefs are vibrant, can provide needed boosts to local economies. In places like Palau’s Rock Islands and the Galápagos, restored ecosystems attract visitors and research funding. 

Nature, oceans, and people: all are interconnected. And the more we learn about the vital linkages that connect all living things on the planet, the more impactful our work to restore islands becomes! 

At Island Conservation, we’re always looking for studies like these to help enrich our practice of holistic restoration. Join our newsletter now to keep up to date on the latest new science—and get stories of hope and recovery delivered right to your inbox every month!