Corals, with their often vibrant colors and stationary presence, are frequently mistaken for rocks or plants. This misunderstanding arises from their appearance on the seafloor, which can seem more geological or botanical. Despite their seemingly inert nature, corals are indeed living organisms, possessing unique biological characteristics that allow them to thrive in marine environments. These complex creatures play an integral role in ocean ecosystems, forming the foundation for some of the planet’s most diverse habitats.
Corals Are Animals
Corals are invertebrate animals, meaning they lack a backbone, and belong to the phylum Cnidaria, classifying them as relatives of jellyfish and sea anemones. Each coral structure is composed of many tiny, individual organisms known as polyps, which live together in colonies.
A single coral polyp has a cylindrical body. At one end, it features a mouth surrounded by a ring of tentacles. The tentacles are equipped with specialized stinging cells called nematocysts, used for capturing food. These polyps anchor themselves to a surface, and their collective activity contributes to the growth of the coral colony.
How Corals Sustain Themselves
Corals employ a dual strategy to obtain the energy and nutrients necessary for their survival and growth. A significant portion of their energy comes from a symbiotic relationship with microscopic algae called zooxanthellae. These algae live within the coral polyps’ tissues, where they perform photosynthesis, converting sunlight into sugars. The organic material produced by zooxanthellae is transferred to the coral host, providing a primary food source.
Beyond their algal partners, corals are also predators, actively capturing food from the surrounding water. They use their stinging tentacles to ensnare tiny plankton and other small organisms. This combination of energy derived from photosynthesis and direct feeding allows corals to flourish in nutrient-poor tropical waters.
Building the Living Reef
Coral reefs are built by the continuous activity of living coral polyps. These polyps extract calcium carbonate from seawater, a process known as calcification, to create their hard, protective skeletons. Each individual polyp secretes a cup-shaped skeleton, called a corallite, which forms the base upon which it lives.
Over time, these calcium carbonate skeletons accumulate, forming the massive, complex foundations of coral reefs. The reef itself is a vast structure comprising both living coral polyps and the layered skeletons of past generations. This ongoing process of calcification by countless polyps means that coral reefs are dynamic, living entities that continuously grow and evolve.