The atoll gap: area, governance, and the under-recognition of a major coral reef system

Global assessments project widespread coral reef degradation under continued ocean warming and acidification, underscoring the urgent need to identify and account for the full diversity of coral reef systems within conservation planning. Atolls are dynamic reef-ocean-land systems whose persistence depends on coral reef sediment production, land-sea connectivity, and cross-ecosystem nutrient subsidies. Some atoll reef environments may also support coral assemblages with elevated thermal tolerance which could mean atolls are, and will increasingly be, important local-to-regional coral sources as global and local impacts continue to limit corals. Using a curated dataset of 310 Indo-Pacific atolls and high-resolution global coral reefscape mapping from the Allen Coral Atlas, we show that 309 Indo-Pacific atolls contain 27,211 km2 of mapped shallow reefscape, representing 41.5% of all Indo-Pacific reef area and 7.8 percent of global mapped shallow reefscape area. This spatial accounting places Indo-Pacific atolls among the world’s major coral reefscape networks by area. We interpret this result alongside literature on atoll ecology, geomorphology, and governance to suggest that atoll-associated reefs merit more explicit consideration in Indo-Pacific coral reef conservation planning, while recognizing that additional comparative evidence on conservation finance, monitoring, protection, and governance would be needed to directly quantify under-recognition.