One of the reasons for current knowledge gaps is the lack of long-term temporal observations of key environmental parameters, such as temperature, salinity, or the pH of seawater. Historically, we either lacked the technology to monitor these parameters, access to such technology was expensive or there was no clear understanding of the need to monitor these parameters. Therefore, to put current changes in perspective, accounting for natural variability, it is necessary to find ways to fill knowledge gaps, and corals can help us to do so!
Reef forming corals precipitate a calcium carbonate skeleton that forms the reef foundation. These skeletons come in all shapes and sizes, from the delicate and intricate branching corals to the massive types that are named as such due to their stable ball- or boulder-shaped skeleton. The skeletons of corals are attractive to paleoceanographers because they can tell us about the past, if you know how to read the stories recorded in their skeletons. This is because corals continuously deposit new layers on top of their older skeleton, thus growing bigger and bigger every year and creating a record of their history. Some massive corals can become real life giants as the can live for several centuries, never ceasing to grow. The oldest massive corals are believed to be nearly a thousand years old. But corals are living organisms that respond to their environment as we do, and their skeleton records these changes in a similar way to trees forming rings. In winter, when the waters are cold, corals tend to grow slower and form a denser skeleton while in summer, when it is warmer, corals usually grow faster and form a less dense skeleton. Therefore the skeleton of a massive coral records this seasonal rhythm in the form of annual bands that resemble the rings in the trunk of a tree.