Atolls: Coral Ringlands Built Over Millennia, Home to a Million and Under Threat from Rising Seas
Atolls are ring-shaped coral islands surrounding lagoons, formed over 1–30 million years through Darwin’s subsidence model (volcanoes rise, reefs grow, island sinks) or the antecedent karst model. About one million people live on atolls, which host substantial seabird populations (≈37 species and ~31 million nesting birds). Notable examples include Great Chagos Bank (largest total area), Kwajalein Atoll (largest lagoon), Kiritimati (largest land area), and Huvadhu Atoll (most islands). They are highly vulnerable to climate change due to sea-level rise and warming, though sediment redistribution can alter land area.
