https://phys.org/news/2018-06-skeleton-formation-young-corals-documented.html

The research was conducted by Prof. Gil Goobes, of the Department of Chemistry at Bar-Ilan University, Dr. Tali Mass, of the Leon H. Charney School of Marine Sciences at the University of Haifa, and Dr. Anat Akiva and Dr. Iddo Pinkas, of the Weizmann Institute of Science in Israel. Their findings were recently published in Nature Communications.

Corals begin their lives as plankton polyp which "swim" freely in the sea. At some point the polyp moves into a "settled" stage in which the formation of the skeleton begins. This is a process in which the polyp secretes calcium carbonate very rapidly in order to form and protect the reef colony. Proper development of polyps to the settled stage is crucial for the proper development of coral reefs.