Masked Boobies
© Tristan Berr

Coral reef islands hold keys for tropical seabird conservation

Many tropical seabirds rely on coral reef islands for breeding, and it shows within BirdLife’s Important Bird and Biodiversity Area (IBAs) network!


In a newly published study, our team emphasizes the importance of coral reef islands for both seabird and reef ecology, with the help of BirdLife IBA data.


Our core message: about 15% of all seabird species use coral reef islands for breeding, with ~30 species concentrating more than half of their global breeding population on these islands. However, despite the fact that contemporary evidence has shown the mutually beneficial interactions between reefs and seabirds, there is still limited knowledge about coral reef islands; a key habitat supporting seabird breeding populations in the tropics. Therefore, particularly in the face of climate change, our study calls for new, global cooperation initiatives to improve the future study and conservation efforts of tropical seabirds.


Coral reef islands: essential, fragile, and… understudied


Left: Carrey islet, New Caledonia. Right: Nukuhione islet, Wallis-&-Futuna. Coral reef islands come in diverse shapes and sizes, but all are vulnerable to the combined effects of reef decline and sea-level-rise due to their low altitude. Pictures © Pascal DUMAS/UNC; Tristan BERR/IRD-UNC

Coral reef islands are low-level, sedimentary structures formed by the accumulation of carbonated debris (e.g. coral skeletons, invertebrate shells) in shallow waters close to active reef ecosystems. They exist throughout the intertropical area and support a unique diversity of plants and animals – which includes large colonies of tropical seabirds.


As low-lying ecosystems, coral reef islands are especially at risk from climate change: reef decline caused by ocean warming and acidification may alter some of their fundamental sedimentary processes, while sea-level-rise threatens to accelerate their erosion.


Unlike other compartments of reef ecosystems, coral reef islands have received limited attention from conservation researchers, meaning that their long-term sustainability – and that of all the living communities that depend on them – remains largely uncertain.


A scattered bedrock for the reproduction of many seabird species


In the absence of international research initiatives dedicated to coral reef island ecology, assessing the dependence of seabird species to these ecosystems was a tricky matter. Among existing data repositories,  the BirdLife IBA network stood as the most comprehensive and wide-ranging set of information, so we undertook a thorough analysis of IBA census records in search of relevant monitoring data.


Over the course of our study, we found that at least 52 seabird species (~15% of all seabird diversity) breed on coral reef islands, and that ~30 species concentrate more than half of their global breeding population on them. For these species, coral reef islands are a cornerstone of future conservation efforts.


Moreover, the vulnerability of these islands to climate change adds to an wide array of existing ecological threats (e.g., invasive alien species, human disturbance, plastic pollution) that already make seabirds one of the most threatened groups of vertebrates.


Left: Murphy’s Petrel (Pterodroma ultima) on the rodent-free, uninhabited atoll of Morane, French Polynesia. Right: Roseate tern (Sterna dougallii) and black-naped tern (Sterna sumatrana) colony, Southern Lagoon of New Caledonia. All three species are highly dependent on coral reef islands for breeding. Pictures © Éric VIDAL/IRD; Tristan BERR/IRD-UNC


A shared responsibility


57 territories spread across 43 countries currently contain IBAs that include both coral reef islands and breeding seabirds. Australia, Bahamas, France, UK and USA account for 55% of these IBAs (209 in total). Promoting the study and protection of seabirds on coral reef islands is therefore a matter of international cooperation, data sharing and coordination of environmental policies.


In total, 209 existing IBAs contain coral reef islands and also host breeding seabird colonies throughout the intertropical area, spread across 43 countries. Source: BirdLife IBA data.


Navigating across seabird and reef conservation


The preservation of seabird colonies on coral reef islands is made all the more relevant by the recent emphasis put on tropical seabirds as contributors to the heath of reef ecosystems. Through guano deposits, seabirds participate in nutrient cycles in reefs, which helps sustain coral growth… and indirectly supports the ecological services that reefs provide to human societies (food sustenance, protection against coastal erosion…). This mutually beneficial interaction between reefs and seabirds is especially strong on coral reef islands, which makes them ideal targets for comprehensive, holistic conservation initiatives.


Masked boobies on Clipperton atoll, Eastern Pacific. Clipperton hosts the largest known colonies of the species and concentrate more than 250 tons of overall seabird biomass, which plays key roles in terrestrial and marine ecological processes on and near the atoll. Picture ©Tristan BERR – IRD/UNC