Atolls and Coral Rings

Short: Atolls are ring-shaped coral reefs enclosing a central lagoon, usually forming over sunken volcanic islands. They’re found mainly in tropical seas such as the Pacific and Indian Ocean.

In more detail: Charles Darwin developed a theory of atoll formation back in the 19th century, which is still largely considered correct today.

In detail

• Darwin’s theory: Coral initially grows around a volcanic island cone, which over time sinks into the sea, while the reef keeps growing as sea levels rise.
• Lagoon in the center: The ring-shaped reef structure encloses a usually calm, shallow lagoon that differs markedly from the open ocean.
• Low land areas: Atoll land areas are often only a few meters above sea level, making them particularly vulnerable to rising sea levels.
• Biodiversity: The sheltered lagoon provides habitat for numerous fish species and marine organisms that would find less protection in the open sea.
• Inhabited atolls: Countries like the Maldives or Kiribati consist largely of atolls and are therefore particularly affected by climate change.
• Fresh water scarcity: Despite surrounding sea masses, atoll residents often have only limited access to fresh water, since rainwater is the main source.
• Erosion risks: Storms and rising sea levels increasingly erode the already narrow strips of land of atolls (korallenriffe-und-ihre-bedeutung, inseln-und-archipele).