Calcification allows corals on the Great Barrier Reef to build calcium carbonate skeletons.
During calcification, reef-building corals extract dissolved calcium and carbonate-related ions from seawater and deposit calcium carbonate beneath their living tissue. Repeated growth by countless coral colonies produces the rigid framework that supports a reef.
The algae living inside coral tissues also contribute indirectly. Through photosynthesis, they provide energy to the coral host, helping support growth and other biological processes. This partnership is one reason reef-building corals thrive in clear, sunlit tropical waters.
Calcification should not be confused with photosynthesis. Photosynthesis is the light-driven process carried out by the coral’s symbiotic algae, while calcification is the mineral-building process that creates the skeleton. Ocean warming and acidification can interfere with coral growth and make reef construction more difficult.