Also known as stinging coral, false coral and itching coral, Millepora alcicornis, or fire coral, is not a true coral at all. Millepora, though classified as coral, are closely related to jellyfish and other hydrozoans.
Millepora translates to "many pores". Fire coral is not a true stony reef-creating coral, but individual Millepora grow together in colonies. The colonies develop and grow in a variety of shapes, including flattened (or encrusting), column-like, branching, box-like, or plate-like. Though they are not true stony coral, Millepora do contribute to the development of coral reefs because of the calcaereous nature of the colonized structures.
Like other reef-building, or anthozoan, corals, Millepora have a calcium carbonate, or limestone, skeleton. Fire coral colonies are individual millepora connected to one another by tubular extensions of the body cavities. Live colonies are usually deceptively coral-like in color, often a yellow-brown hue with pale edges or branch-tips. Infrequently they can be green or pink in color.
Fire corals are classified as hydrozoa because unlike anthozoan corals they have specialized stinging polyps called nematocysts. More specifically, they have two types of polyps: gastrozooids, which are used for feeding; and dactylozooids, which are for defense and for capturing prey. Millepora colonies lie in wait for unwary plankton, which they then paralyze and consume.
Like anthozoan corals, fire corals contain a symbiotic algae called zooxanthellae within their tissues. The algae helps provide the coral with nutrients. Unlike anthozoan corals, Millepora are the only reef-building corals that reproduce in two distinct generations. The grown polyps reproduce asexually by producing and releasing tiny jellyfish-like medusae from specialized cup-shaped structures known as ampullae. The medusae carry reproductive organs, which release eggs and sperm, and newly fertilized eggs develop into larvae from which a new colony of polyps develops. Fire corals can also spread asexually by fragmentation.
The common name, fire coral, is an apt moniker. Like their jellyfish relatives, fire coral's nematocysts deliver a powerful sting feared by divers for its burning intensity. Unlucky divers who have grabbed fire coral by mistake compare the sting to that of a Man o'War jellyfish, and the pain has been known to cause vomiting or even fainting. Meat tenderizer and urine are common folk remedies, but by all accounts the stings just hurt like hell no matter what you apply. If you SCUBA or snorkel, it's a good idea to steer clear of any and all coral. Touching or handling coral is very damaging to the delicate coral reef ecosystem, and it could really ruin your vacation.
Though they have no intrinsic economic value, fire coral's nasty sting is thought to play a role in protecting the coral reefs on which the colonies thrive. Regular stony coral is extremely sensitive to touch, but the threat of a fire coral sting is enough to discourage less scrupulous divers who might otherwise touch or break common coral.
Fire coral is common in tropical waters worldwide, particularly in the Indian, Pacific, and Atlantic Oceans, and is extremely common in the Caribbean. Fire coral is not considered to be globally threatened, though one particular Panamanian species, Millepora boshmai, is thought to have become extinct in 1998 from widespread bleaching.
Bleaching is the partial or complete destruction of the symbiotic algae inside the coral polyps, and is most often caused by environmental stress such as drastic variations in salinity or temperature, garden-variety pollution, or increased turbidity. Fire coral are more susceptible to bleaching than many hardier forms of anthozoan (stony) coral, and may wind up on the endangered species register soon.
Fire coral is already listed in the Convention on International Trade in Endangered Species, or CITIES. It is illegal to transport either living specimens or artifacts made of fire coral into the 158 countries that have signed the CITIES convention.