atól

An atól, sometimes written as atól or atóló in various languages, is a ring-shaped coral island or chain of islands that surrounds a central lagoon. The term is used across several languages to denote the same geographic feature as the English word “atoll.” Atóls are typically low-lying and occur in tropical and subtropical seas.

Formation and appearance: Atóls form from coral reefs that grow around the rim of a submerged volcanic island. Over time the volcanic island subsides while the reef keeps growing upward, creating a circular or horseshoe-shaped ring with a central lagoon. In many cases one or more islets appear along the rim, giving the atól a broken or segmented contour.

Morphology and ecology: Most atóls have a low crest rising only a few meters above sea level. The central lagoon is usually shallow and may host seagrasses, patches of mangroves, and diverse marine life. Soils on the ring are thin and salinity and wind exposure limit terrestrial vegetation. Reefs and lagoons support a wide range of fish, invertebrates, and birds, making atóls important for local fisheries and biodiversity.

Distribution and human use: Atóls are most abundant in the Indo-Pacific region and the Indian Ocean, with many examples in the Maldives, Kiribati, Tuvalu, and the Marshall Islands. Fewer instances occur in the central Pacific and other basins. Many atóls are sparsely populated or uninhabited; communities often rely on rainwater for freshwater and reef resources for food. Their low elevation makes them highly vulnerable to storms and sea-level rise, leading to conservation measures and, in some cases, protected-area designations. Tourism is an increasing economic activity on several atóls.