Seabird guano and native trees keep islands above rising seas: Study.
A multi-university team reports in Science Advances that seabird guano and native vegetation help atoll islands build reef, sediment and soil, enough on rat-free islands to match sea-level rise projected under 2 degrees Celsius of warming.
A study in Science Advances finds that atoll islands with abundant seabirds and native forests are better equipped to keep up with rising seas. The researchers used data from 28 atoll islands in the Seychelles, the Chagos Archipelago and Tetiaroa in French Polynesia.
Seabirds move nutrients from open-ocean feeding areas to land through their guano. The team traced that energy through land and marine ecosystems and focused on three island-building processes: reef accretion, sediment production and soil stabilization. Atoll islands are built and maintained by biological processes, so each of these matters to their survival.
On rat-free islands with many seabirds, the carbonate reef structure grew 1.5 to 1.8 times faster than on islands with rats, according to the authors. Parrotfish, which turn reef material into sand, grew larger and processed sediment more efficiently, and rat-free islands had 2.3 to 2.8 times as much sediment available. Around rat-infested islands, reef growth was already outpaced by current sea-level rise.
On land, islands with more than 75% native vegetation, a common restoration target, had 4.6 times greater fine root length in soils. The researchers say these dense root mats help protect islands from erosion and storms. Introduced coconut palms, by contrast, have shallow, rounded root balls. The combined boost on rat-free, seabird-rich islands was enough for reef growth to keep pace with sea-level rise projected under 2 degrees Celsius (3.6 degrees Fahrenheit) of warming until 2100.
Lead author Nicholas Graham of Lancaster University said rewilding, meaning removing invasive predators and planting native vegetation, could be an alternative to engineering defenses on sparsely populated or uninhabited atolls. Co-author Cassandra Benkwitt of The Nature Conservancy called it a "win-win-win" for land, sea and climate resilience.
Stephanie Borrelle of BirdLife International, who was not involved, said the work firmly establishes the importance of seabirds. Seabirds are the most threatened group of birds, with 30% of species at risk of extinction, and invasive predators such as rats are considered the major threat.
At a Glance
- Researchers used ecological data from 28 atoll islands in the Seychelles, the Chagos Archipelago and Tetiaroa, French Polynesia.
- Reef structure grew 1.5 to 1.8 times faster on rat-free islands than on rat-infested islands.
- Rat-free islands with abundant seabirds had 2.3 to 2.8 times as much sediment available for island maintenance.
- Islands with more than 75% native vegetation had 4.6 times greater fine root length in soils.
- Sea-level rise has recently reached about 3.5 centimeters per year, roughly double the long-term average since 1901.
Sources
This brief was written by Brightside Report from the reporting linked above. Spot an error? Request a correction.