No doubt you have seen some fantastic examples of coral while diving in various locations, particularly in warm tropical water; and while corals sometimes blend into the background and are mistaken for plants or rocks, they are incredibly important to the health of oceans worldwide.
Hard Coral Basics
The hard corals divers encounter most often normally live in water 60 meters deep or less, but there are coral colonies living in cold, deep water as well, with some species having been discovered as far as 3,000 meters below the ocean’s surface.
Most corals create heads of genetically identical coral polyps, each of which is spineless, never longer than a few centimeters, and usually just a few millimeters in diameter. Each coral polyp has a cetral mouth and minuscule tentacles, and each forms an exoskeleton at its base. Formed of calcium carbonate, these tiny exoskeletons remain when old polyps die and new ones hatch; they eventually come together to form larger skeletons, and in essence, build the magnificent reefs we love to dive.
While individual coral heads grow via asexual reproduction of polyps, many coral species also breed sexually via spawning, normally at night, during the full moon. Shallow water corals are often nourished via symbiotic algae that live inside their tissue, although some species, particularly deep water varieties, are capable of catching plankton and small fish, often with the aid of the ocean’s currents.
Commonly Encountered Hard Corals
Knowing about the corals you encounter and understanding the way that they function in the marine environment can greatly enhance your overall enjoyment of diving. While there are thousands of species of coral and many different types are found in the world’s oceans, some are more commonly encountered than others. Here are just some of the hard corals you will probably find forming reefs, living on wrecks, and clinging to rocks and walls.
Pillar Corals – Normally rising up from the sea floor and capable of living on either flat or sloped surfaces at depths between 1 and 20 meters, pillar corals do not tend to have secondary branches. Some pillar corals grow to be over 2 meters tall, sometimes growing together in masses. You can usually see their polyps feeding during the daytime – these corals look as though they are covered in thick hair. Most pillar corals are found in the Western Atlantic Ocean, Caribbean Sea and Gulf of Mexico.
Brain Coral – With a grooved surface that looks very much like the surface of a brain, these corals are capable of living an estimated 900-1,000 years. Colonies of brain coral can be enormous, with some growing to be as tall as 6 feet high. While different varieties of brain coral are widely distributed in shallow reefs throughout the world’s oceans, it is considered to be endangered as it is subject to disease and destruction. On night dives, you can see the brain corals tentacles extended to feed.
Blue Corals – Featuring blue skeletons and blue or greenish-grey polyps, blue corals are found in tropical waters, intertidal reef flats, and on upper reef slopes throughout the Indo-Pacific region, including Japan’s Ryukyu Islands, Australia’s Coral Sea, and in American Samoa. The world’s largest known blue coral colony is off Ishigaki Island, in Japan’s Yaeyama Islands. Individual blue coral polyps live in tiny tubes inside the skeleton, and are connected via a thin tissue layer that covers the entire structure. The species is listed as vulnerable by the International Union for the Conservation of Nature (IUCN).
Tube Corals - Tube Corals are found in a variety of forms and colors. With large polyps and a stony surface, these species tend to be found in warm water throughout the world’s oceans. Some examples include Orange Cup Coral and Black Sun Coral.
Elkhorn Corals – One of the most important reef builders in the Caribbean, and also commonly found in Florida’s reefs and in other warm climates, Elkhorn coral is a shallow water species. It is fast growing can get to be as large as nearly 4 meters in diameter. The coral’s branches can be as long as 2 meters or so, and provide shelter to reef fish and crustaceans. Since 1980, populations have been declining steadily, mostly due to disease, lack of biodiversity, coral bleaching, and temperature and salinity problems associated with global warming. Many Elkhorn coral species and their close relative, Staghorn coral, are listed as endangered species.
Star Corals – with huge polyps that can grow to be the size of a person’s thumb, star corals form massive boulders, and sometimes even develop into enormous plates that cover large areas. Found in the Caribbean and in other warm waters, various varieties of star corals can be seen extending their polyps to feed once the sun goes down. They tend to be found at depths between 10 and 35 meters.
Table Corals – While table corals do form branches, they grow in flat platelike formations. Usually fairly dull in appearance, with colors ranging from tan to green depending on the algae they host, these corals provide shelter to a wide array of marine life that can be found both above and beneath its plates.
Black Coral – While Black Corals are not stony coral species, they do form hard skeletons. Some of the most beautiful corals to encounter, they are usually found in deep water, often attached to walls or wrecks. One exception is the black coral population in New Zealand’s Milford Sound, where the water is dark enough to shelter the creatures. There are more than 230 known black coral species with dark brown to black skeletons and living tissue in colors ranging from black to orange or red, to shades of green, yellow, or white. Many of these are endangered, as black coral is often harvested for use in jewelry; sadly, Hawaii still calls black coral its state “gem”.
According to IUCN, more than a third of the world’s reef building coral species face extinction. You can do your part to protect it by adhering to a strict no touch policy – even a light touch can kill coral polyps. If you’re a new diver, be sure you have a good handle on buoyancy control before getting too close to coral, not only will you damage it if you collide with it, but it can often sting or scrape you, causing a great deal of pain and even scarring. Never buy coral products, and if you keep an aquarium, do not support the harvest of living coral. If we all do our part, the coral reefs we love stand a better chance of returning to health.