Skeleton-forming responses of reef-building corals under ocean acidification

Abstract

Ocean acidification is increasing in frequency and is considered one of the most important causes of severe damage to global coral reefs. Therefore, there is an urgent need to study the impact of acid stress on the growth patterns of major reef-building corals. Here, we studied the skeleton forming strategies of four widely distributed coral species in a simulated acidified habitat with a pH of 7.6-7.8. We reconstructed and visualized the skeleton building process, quantified elemental calcium loss, and determined gene expression changes. The results suggest that different reef-building corals have diverse growing strategies in acidified seawater. A unique cavity-like forming process starts from the inside of the skeletons of Acropora muricata, which sacrifices skeleton density to protect its polyp-canal system. The forming patterns in Pocillopora damicornis, Montipora capricornis, and M. foliosa were characterized by osteoporosis, exhibiting disordered skeletal structures, insufficient synthesis of adhesion proteins, and low bone mass, correspondingly. In addition, we found that skeletal areas near coral polyps suffered less and had later acidified damage than other skeletal areas in the colony. These results help to understand the skeleton-forming strategies of several major coral species under acid stress, thereby laying a foundation for coral reef protection and restoration under increasing ocean acidification.