The most common and numerous island type across the Pacific basin are atolls. Even though these island systems harbor only a few endemic species, atolls are globally important nesting sites for seabirds and sea turtles, roosting sites for migratory shorebirds, and refugia for Oceania's unique lowland flora and fauna. While atolls were extensively surveyed for their island biodiversity in the second half of the twentieth century, many remain unmapped, leaving important knowledge gaps for Pacific biodiversity, biogeography, and conservation. Here, we report on a terrestrial biodiversity survey of Manuae atoll, Cook Islands. Our assessment revealed that Manuae atoll harbors seabird colonies and is an important green sea turtle nesting site. Furthermore, we found at least 100 bristle-thighed curlews (Numenius tahitiensis) overwintering on the island (ca. 1% of the estimated global population), which under international evaluation criteria renders the atoll an important overwintering area that warrants protection and recognition. While our island biodiversity assessment and mapping, including vascular plants, land crabs, reptiles, and birds, reveals that Manuae atoll is an important refuge for lowland island biota within the Cook Islands, we also documented the presence of key introduced species, including Pacific rats (Rattus exulans) and yellow crazy ants (Anoplolepis gracilipes), and a colonial legacy in the overall habitat composition from the abandoned copra plantation. Our findings on the terrestrial biodiversity of Manuae atoll fill an important knowledge gap in island biodiversity data from the Cook Islands. This information can support future ecological and biodiversity research, as well as inform management, protection, and restoration planning.
