Coral reefs look like rocky, underwater formations and many people think they are just that: ridges of strangely shaped, stone-like growths that extend over a certain area of seabed. However, a coral reef isn’t a “thing” – it’s actually a community of living beings, many of them invisible to the naked eye, yet making up a complex aquatic universe that provides habitat and lives in symbiosis with numerous other creatures of the sea.
Coral reefs look as if they were made of stone – and they are, indeed, to a certain extent, lime-stone formations. Corals are actually tiny animals, polyps that secrete a skeleton of calcium carbonate. It is this stony skeleton that we see and perceive as a stony coral, with the animals wrapped into the skeleton remaining small, fragile and in most cases visible only during the night. The other inhabitant without which there would be no coral reef are zooxanthellae algae, single-celled organisms that live in symbiosis with the coral polyps and produce the food the corals need by engaging into a process called photosynthesis – that is, by harvesting the energy that comes from the rays of the sun and transforming it into chemical energy.
The coral polyps living in a symbiotic relationship with their zooxanthellae form the basic layer of coral reefs and they build the formations that give home and shelter and provide food to a huge number of other creatures of the sea, to create complex ecosystems. Coral reefs are populated by small animals such as sponges, crabs, shrimps, anemones, microscopic crustaceans, worms, sea cucumbers, sea urchins, snails, scallops and many others.
There are a number of species that dwell on coral reefs, and there are many others that visit the reefs only occasionally, for a certain purpose, such as feeding or laying their eggs in the sheltered crevices and coves of the coral formations.
Some species of sharks and rays live exclusively in coral reef biomes;
Wrasses are also important members of the community, responsible for cleaning the reef area from parasites;
Predators such as eels are only visitors to the reef areas, but they play an important role in the balance of the ecosystem by feeding on smaller animals.
Besides zooxanthellae, there are other life forms that rely on photosynthesis as a means of survival, too. Given their way of nourishing themselves, these life forms are called plants, but only some of them, mangroves and some seagrass types, are true plants – the others are, in fact, algae. Algae create formations that look like plants with roots and long leaves, but are similar to land plants only in their appearance. Reef plants form extended meadows on and around the reefs, serving as sources of food, shelter and nursing place for numerous coral reef species. Coral reefs are among the richest and most complex communities on Earth and they are, at the same time, among the most delicate ones, too. Each member of the community has its own role in the ecosystem – if one is removed or becomes unable to function properly, the hindrance will affect the entire community.