They may look like plants, but corals are actually animals. They come in many shapes, sizes and colors, but nearly all corals live in colonies formed by many tiny, genetically-identical individuals, called polyps.
There are soft corals with thick, pliable branches and thin, flexible fan corals that anchor in the mud or sand. Some are found deep in the ocean’s dark, cool waters, while others inhabit the warm, shallow tropics.
Stony corals produce and grow hard, calcium carbonate skeletons (like human skeletons that develop over time). They are the builders and architects of the oceans, forming reef structures as they grow. So, corals are both animals and habitat. For this project, Smithsonian scientists focused their efforts on a species of stony coral, called elkhorn coral (Acropora palmata).
Elkhorn coral is named for its thick branches which resemble an elk’s antlers. It is one of the largest coral species in all the oceans, and its unique shape and structure helps protect shorelines against damaging wave action. Elkhorn corals also create hiding places for fish and other marine animals. So, in some sense, they are the apartments of the oceans.
Like most coral, elkhorn coral reproduces in two ways. The first is by fragmentation, which happens when small pieces of an elkhorn coral break loose. These pieces can jam into crevices, reattach and form new colonies that are clones of the original. Coral can also reproduce through sexual reproduction, which creates new individuals. Those individuals may have new genetic traits that could help coral adapt to changing ocean conditions.
Many corals, including elkhorn, are hermaphrodites – which means they produce both male and female gametes. Most elkhorn coral spawn for just a few nights each summer, following a full moon. About three hours after sunset, the corals simultaneously release their egg-sperm bundles into the water. The bundles float to the surface of the sea, where they break apart and become fertilized eggs.