Rat-free atolls with seabirds have reefs growing up to 2.5 times faster
A Lancaster-led study finds reefs around rat-free atolls grow 1.8 to 2.5 times faster than those around rat-infested islands. The comparison is across islands and the rates are calculated potentials, so it says little about one island's recovery after eradication.
The Scientist · Science desk
Sediment production on lagoonal and ocean-facing reefs at islands with seabirds is estimated at 2.3 to 2.8 times higher. Lagoonal reef growth at rat-free islands is 1.8 times that at rat-infested islands. The data cover 28 atoll islands.
| Figure | Value | Note | Claim |
|---|---|---|---|
| Sediment production, seabird islands, at least | 2.3 times higher | estimated; up to 2.8 times higher | 9 |
| Lagoonal reefs, rat-free | 1.8 x reef growth | 6 | |
| Atoll islands in the data | 28 islands | 2 |
What happened
- The team combined ecological datasets for 28 atoll islands in the Seychelles, the Chagos Archipelago and Tetiaroa atoll in French Polynesia.
- Seabirds and native vegetation had a positive effect on three processes tied to resilience: coral reef growth, sediment production and soil stabilization.
- Corals grew much faster and calcified faster on reefs around islands with healthy seabird populations than at bird-free islands, forming more hard reef substrate.
- Sediment production potential, linked to greater parrotfish biomass, was estimated at 2.3 to 2.8 times higher on lagoonal and ocean-facing reefs at islands with seabirds.
Why it matters
- decision Managers of rat-infested islands with old coconut stands face two separate jobs, eradication and replanting, and the lead author's case is for doing both.
- capability Reef accretion potential gives planners a way to put a number on what an eradication might add to reef growth before they commit to one.
- constraint Where coconut dominates, as across Pacific atolls, the study's evidence is one atoll deep, so carrying the Indian Ocean results over is an assumption.
The study, published in Science Advances, used seabird census counts to estimate how much "energy" the birds bring from the open ocean to each island, and how the nutrients in their droppings affect the island and the marine ecosystems around it [1][3]. The comparison behind the growth ratios is then between islands. The study treats rat-free islands as islands with abundant seabirds [6], so rat status is the grouping variable and seabird abundance is inferred from it.
Reef growth is key to reducing wave-driven erosion of island coastlines [12]. Co-author Casey Benkwitt of The Nature Conservancy said the accretion rates for rat-free, bird-populated lagoonal reefs "would be sufficient to closely keep up with predicted sea-level rises up to the end of the century", under a 2 degrees C warming scenario [7]. Benkwitt added: "In contrast, reef growth rates without seabird populations are predicted to have limited ability to keep up with projected sea-level rises." [8]
That statement covers lagoonal reefs under one warming scenario [7]. The thing the comparison doesn't tell you is how long a seabird colony takes to return after rats are removed, or whether a formerly infested island's reefs then grow at the rat-free rate. In our view, answering that takes islands followed through an eradication, and a comparison across islands cannot supply it.
Nick Graham, the lead author, described atolls as active systems. "Atoll islands are not static; they are naturally active systems that can change and adapt to their environmental conditions if they are allowed to do so," Graham said [14]. Rats arrived as stowaways on boats in previous centuries, and many islands lost their seabirds to the combination of lost roosting habitat and those predators [11].
The replanting half of the proposal covers a lot of ground. Coconut plantations are estimated to dominate around 60% of Pacific atoll forests [10].
What to watch
- Seabird and reef measurements from islands before and after a rat eradication, which would test the cross-island comparison directly.
- Pacific atoll data beyond Tetiaroa, where coconut plantations cover most of the forest.
- Measured shoreline change on islands with recovering seabirds, to check the modelled sediment and reef-growth potentials.
Clarity's read
What the record supports and how the coverage leans. The claims behind it follow.
Reality
- Evidence55
- Adoption
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- Hype gap+20
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Claim ledger
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- [1]
The study was published in the journal Science Advances by an international team of researchers led by marine scientists at Lancaster University.
- [2]
The researchers combined ecological data sets for 28 Indian and Pacific Ocean atoll islands across the Seychelles and the Chagos Archipelago in the Indian Ocean, and Tetiaroa atoll in French Polynesia in the Pacific.
- [3]
Using seabird census data, the researchers estimated the amount of 'energy' seabirds bring from the open ocean back to each atoll island and how the nutrients deposited in their droppings influence the islands and surrounding marine ecosystems.
- [4]
The researchers found that the presence of seabirds and native vegetation has a positive effect on three processes that support atoll island resilience to sea-level rise: coral reef growth, sediment production and soil stabilization.
- [5]
Corals grow much faster on reefs around islands with healthy seabird populations than on reefs around bird-free islands, and these nutrient-enhanced corals also calcified faster, forming more hard reef substrate.
- [6]
Reef growth rates on lagoonal and ocean-facing reefs around rat-free islands, and therefore with abundant seabird populations, were 1.8 and 2.5 times greater, respectively, than those on reefs around rat-infested islands.
- [7]
Co-author Casey Benkwitt of The Nature Conservancy said the reef accretion rates for rat-free, bird-populated lagoonal reefs "would be sufficient to closely keep up with predicted sea-level rises up to the end of the century" under a 2 degrees C warming scenario.
- [8]
"In contrast, reef growth rates without seabird populations are predicted to have limited ability to keep up with projected sea-level rises."
- [9]
Sediment production potential, due to greater parrotfish biomass and other sediment-producing organisms, was substantially higher for islands with seabirds, with an estimated 2.3 to 2.8 times higher sediment production rates on lagoonal and ocean-facing reefs.
- [10]
Coconut plantations are now estimated to dominate around 60% of Pacific atoll forests.
- [11]
Many tropical islands have lost their seabird populations due to a combination of lost roosting habitats and predators in the form of invasive rats, which arrived as stowaways on boats in previous centuries.
- [12]
Reef growth is key to reducing wave-driven erosion of island coastlines.
- [13]
Lead author Nick Graham of Lancaster University said that replacing old, abandoned coconut palm plantations with natural vegetation, and restoring seabird populations by eradicating invasive rats, could be key to the survival of these tiny low-lying islands.
- [14]
"Atoll islands are not static; they are naturally active systems that can change and adapt to their environmental conditions if they are allowed to do so."
- [15]
Using the data, the researchers calculated the 'reef accretion potential' for the islands, revealing how conservation measures such as rat eradication might influence overall reef growth.
- [16]
The Pacific part of the 28-island dataset comes from one atoll, Tetiaroa in French Polynesia; the other locations named are the Seychelles and the Chagos Archipelago in the Indian Ocean.
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Sources
1 independent publisher whose own reporting we read for this story.
- phys.orgRemoving rats and restoring native plants could help atolls withstand rising seas
1 article · October 14, 2026
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