Seabird guano and native trees help tropical atolls resist sea level rise

Tropical atoll islands appear highly vulnerable to climate-driven sea level rise, yet a new study reveals that healthy seabird populations and native forests can enable these low-lying lands to accrete sediment fast enough to keep pace with the ocean's advance.

Researchers examined sediment cores and ecological records from several Pacific and Indian Ocean atolls. They found that seabird guano delivers massive amounts of phosphorus and nitrogen from open-ocean feeding grounds to islands, dramatically boosting soil fertility and plant growth. In turn, dense native tree cover traps wave-borne sediment and organic matter, allowing islands to build elevation naturally.

Without these biological contributions, many atolls erode or drown under current projections of 0.5 to 1 metre of sea level rise by 2100. The findings highlight a feedback loop where seabirds act as living nutrient pumps, directly supporting the vertical growth that determines whether an island survives.

What happened

The peer-reviewed research combined field measurements of guano deposition rates with historical satellite imagery and core samples that track island growth over decades. Islands retaining intact seabird colonies and native vegetation showed consistent vertical accretion even during periods of accelerated sea level rise, while nearby degraded islands lacking these features experienced net loss.

Seabirds forage across vast marine areas, then return to roost and nest, concentrating marine-derived nutrients on land. This guano enrichment promotes rapid forest development, whose root systems stabilize sediment and encourage further deposition during storms. The study quantifies how this nutrient subsidy can increase accretion rates by several millimetres per year, enough to match moderate sea level rise scenarios.

Why it matters

Ecological feedback loops

The research underscores how interconnected marine and terrestrial systems shape island futures. When seabird numbers decline due to overfishing, invasive predators or habitat loss, the nutrient pipeline shuts down, forests thin and islands become more susceptible to erosion. Restoring seabird colonies could therefore serve as a powerful nature-based adaptation strategy.

Implications for atoll nations

For communities living on low-lying coral islands, preserving or reintroducing seabirds and native trees offers a locally driven path to resilience. This approach contrasts with expensive engineered solutions such as sea walls, which often fail to address underlying sediment deficits.

Links to broader conservation

Similar nutrient-transfer dynamics appear in other ecosystems where large animals move resources across landscapes. Protecting seabirds therefore delivers dual benefits, safeguarding both marine food webs and terrestrial landforms against climate impacts.

What comes next

Scientists call for urgent protection of remaining seabird colonies on atolls and active restoration projects that remove invasive species and replant native trees. Monitoring programmes will track whether enhanced guano deposition can keep pace with accelerating sea level rise under higher-emission pathways. International climate funds may increasingly support such ecological restoration as cost-effective adaptation for small island states ahead of COP30 discussions on loss and damage.

Continued research will examine whether artificial nutrient additions can mimic natural guano effects on islands where seabirds have already disappeared. Results could inform pilot projects across the Pacific and beyond, testing if strategic rewilding can literally lift islands above the waves.

Sources

https://news.mongabay.com/2026/10/seabird-guano-and-native-trees-keep-islands-above-rising-seas-study/