Atolls are globally important sites for tropical seabirds

Abstract

Seabirds play critical roles on islands. By catalysing terrestrial and marine productivity through guano nutrient input, seabirds support natural island functioning. In the Indo-Pacific, atolls comprise one-third of all islands but only ~0.02% of island area. The importance of atolls as seabird nesting grounds has been historically neglected except on a few key atolls. We compiled a global dataset of seabird surveys on atolls and modelled seabird distribution and nutrient deposition on all Indo-Pacific atolls. We found that atolls are breeding sites for 37 species, ranging from a few dozen to more than 3 million individuals per atoll. In total, an estimated 31.2 million seabirds nest on atolls, or ~25% of the tropical seabirds of the world. For 14 species, more than half of their global populations nest on atolls. Seabirds forage more than 10,000-100,000 km² around an atoll and deposit, on average, 65,000 kg N and 11,000 kg P per atoll per year, thus acting as major nutrient pumps within the tropical Indo-Pacific. Our findings reveal the global importance of atolls for tropical seabirds. Given global change, conservation will have to leverage atoll protection and restoration to preserve a relevant fraction of the tropical seabirds of the world.