A reef with a central lagoon
The tropical atoll represents one of the coral reefs best known and most easily recognized by its ring shape, which surrounds a central lagoon of warm water.
These lagoons usually have depths of between 30 and 80 metres and connect to the open sea through natural channels, through which water circulates, driven by waves and currents.
The origin of atolls: from volcanoes to reefs
The origin and formation of atolls have been the subject of numerous scientific studies. Today, it is accepted that these structures formed millions of years ago from ancient volcanic islands.
As these islands slowly sank, the corals continued growing toward the surface, staying in well-lit areas. Over time, the volcano disappeared beneath the sea, leaving only the ring of coral, giving rise to the atoll.
From reef to island
The part of the atoll that rises above the surface can, thanks to the combined action of wind, waves and erosion, accumulate sediment and form fertile soil.
This allows plants such as coconut palms, breadfruit trees and other tropical plant species to grow. Seeds arrive carried by birds, wind or ocean currents, turning some atolls into true tropical islands.
Fragile and valuable ecosystems
Atolls are ecosystems of great beauty and biodiversity, but also extremely fragile in the face of climate change, rising sea levels and ocean warming.
Their conservation is key to protecting both coral reefs and the human communities that depend on them.
