Corals are truly fascinating creatures. They can be found all around the world, from deep, cold oceans to warm and shallow waters. Although they look very much like plants, they are in fact animals, a special kind of invertebrate, closely related to the jellyfish and sea anemones. They vary in many shapes, sizes and colors, but their underlying structure is always the same – they have a stomach, with a single mouth, surrounded by tentacles. A single individual is called a polyp, but most live in groups of hundreds of thousands, known as colonies.
There are two distinct types of coral – soft, which sway gracefully and tend to be very colorful, and hard, which accumulate calcium from the seawater and use it to create a type of skeleton. The latter are also known as reef-building corals and their colonies build giant carbonate structures over millions of years. These coral reefs are enormous ecosystems, home to countless plants and animals and are the biggest living structures on the planet.
Although different species of corals have adapted to many diverse conditions, they are very sensitive to changes in their surroundings. Slight variations in the temperature, acidity or pollution can have devastating consequences. For example, the density of their skeleton depends on the water temperature, the amount of light and available nutrients. These changes, which occur periodically with the seasons, can be seen in the rate, in which the corals are growing. Their skeletons form growth rings, similar to the ring of trees and from them scientists can not only determine their age, but also the climate conditions throughout the years. Using this data, they construct a record and detect deviations from the normal pattern, which helps to make more accurate predictions about the future. This is instrumental in the fight against global warming, which is in itself the fight to preserve the corals from extinction.