How does land subsidence help coral reefs grow upward?

According to the subsidence theory proposed by Charles Darwin, land subsidence facilitates the upward growth of coral reefs by allowing the reef structure to maintain its position relative to the ocean surface.12

As a volcanic island or the underlying ocean floor gradually sinks, the reef-building organisms—which are restricted to shallow, sunlit waters—continue to grow upward and outward toward the open water to remain within their optimal depth range. This process allows the reef to persist even as its foundation descends. Over thousands of years, this continuous upward accumulation can transform a fringing reef into a barrier-reef and eventually into an atoll, where the original volcanic island is completely submerged, leaving behind a ring of coral enclosing a lagoon.12

While subsidence is a key mechanism, modern science also recognizes that fluctuations in sea level, particularly those driven by glacial cycles during the Pleistocene Epoch, have significantly influenced the development and upward growth of many reefs.123