How does coral growth allow an atoll lagoon to persist while its foundation sinks?

An atoll lagoon persists through the continuous upward growth of coral and the accumulation of calcareous sediment. As the underlying volcanic foundation subsides, the reef-building organisms maintain their position by growing toward the surface, where conditions are optimal for their survival.123

This process, famously described by Charles Darwin, allows the reef structure to keep pace with the sinking island. Because the reef grows most vigorously at its seaward edge, it forms a protective rim that encloses a central area. This interior space remains a lagoon as long as the coral maintains its growth at a suitable level relative to the sea level. Over time, the lagoon floor is maintained by the ongoing deposition of reef-derived materials and coral growth, ensuring the feature persists even as the original volcanic peak disappears beneath the ocean surface.213