A 183% increase in fish biomass near Ulong Island, Palau, now directly supports the livelihoods of those who depend on the reef. This significant ecological recovery follows the removal of invasive rats from the island in 2024. Scientists found an 80% rise in leaf nitrogen at the same reef site, roughly one year after the restoration effort.
Restoring Livelihoods
Nathaniel Hanna Holloway, a marine ecologist at the Scripps Institution of Oceanography, emphasized the direct impact. He stated, "These early signals from Ulong show how quickly ecosystems can rebound when stressors are removed. For the first time in Palau, we're seeing measurable evidence of seabird-driven nutrient flow returning to the land and sea. It's powerful proof that terrestrial action spills over into benefits for surrounding reef communities, which people rely on for their livelihoods." The collective well-being of the island nation's working people is directly tied to the health of these marine environments.
The findings offer the first experimental evidence that seabirds, returning after invasive rodents are removed, can transport nutrients from land into the sea. This process helps reef ecosystems recover sooner than previously anticipated. The research took place on Ulong Island in the Republic of Palau, a Western Pacific island nation.
Ecological Rebound
Scientists from Island Conservation and the Scripps Institution of Oceanography at the University of California San Diego monitored Ulong Island both before and after the rat removal. They tracked seabirds, nutrient levels, reef fish, and other marine life. These results were then compared with nearby Ngeruktabel, an island where invasive rats persist. Coral Wolf, Conservation Impact Program Manager at Island Conservation, noted the speed of the change. "Seeing measurable ecological change just one year after restoration is extraordinary," Wolf said. "It demonstrates the power of local leadership and science working together to heal island ecosystems from ridge to reef."
The return of seabirds served as a clear indicator of recovery. The endangered Palau Ground Dove was detected more frequently after the restoration work. Calls of Bridled Terns increased by 286%, while Brown Noddy and White Tern calls rose by approximately 50% compared to the control island. Seabirds feed in the ocean but return to land to nest. Their droppings, known as guano, carry vital nutrients from the sea back to the islands. Rain then washes some of these nutrients into nearby coastal waters, supporting marine life.
Researchers also observed changes in the island's soil and surrounding waters. Nitrogen signatures declined more slowly on Ulong than at other sites. This finding aligns with expectations if seabird guano was beginning to replenish nutrients in the soil and marine environment. Fish populations responded earlier than anticipated. The significant increase in fish biomass around Ulong suggests that the returning nutrients were already bolstering reef productivity.
Collective Action's Impact
Invasive rats represent one of the most significant threats to island ecosystems globally. They prey on bird eggs and chicks, preventing many seabird populations from recovering. Observational studies had previously suggested the link between land restoration and marine recovery. However, the Ulong project marks the first experimental study to demonstrate this process through before-and-after monitoring and comparisons with another island. The findings underscore how closely land and sea are connected, revealing that restoring island ecosystems can directly improve the health of nearby oceans, benefiting the communities whose livelihoods depend on them. The Island-Ocean Connection Challenge, or IOCC, facilitated this research, according to Island Conservation.