Hard and Soft Corals

Coral colonies are composed of many tiny, cup-shaped animals called polyps, which are related to jellyfish. A single coral polyp may be as large as a saucer or smaller than the head of a pin. Millions of polyps working together in a cooperative colony generation after generation create the limestone skeletons that form the framework of the beautiful coral reef.   Corals begin life in tropical waters as free-floating larvae. After a relatively short period of time, the larva eventually attaches itself to a hard surface and becomes a polyp. Polyps divide asexually and form colonies. Coral colonies reproduce both sexually and asexually. In sexual reproduction, the coral polyps release both eggs and sperm into the water. (This is also known as coral spawning.) One type of asexual reproduction occurs when fragments of coral are broken off as a result of storm action. The broken pieces of corals usually survive and continue to grow and produce a new colony. This process is referred to as “fragmentation”.

Common NameScientific NameRangeDescription
 Coral ReefsAgaricia grahamaeWest Wall Ecosystem Orange Canyon Grand Cayman (Steven Smeltzer)Surge zone, Molokini Crater, Maui Hawaii, 15 feet near rim of crater (Steven Smeltzer)Soft and Hard Coral on Pinnacle Grand Cayman (Steven Smeltzer)Surge zone Molokini crater (Steven Smeltzer)
The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%. Coral reefs are estimated to cover 284,300 square kilometers (109,800 sq mi), just under one tenth of one percent of the oceans’ surface area. Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26–27 °C (79–81 °F), and few reefs exist in waters below 18 °C (64 °F). However, reefs in the Persian Gulf have adapted to temperatures of 13 °C (55 °F) in winter and 38 °C (110
°F) in summer. Deep water coral can exist at greater depths and colder temperatures at much higher latitudes, as far north as Norway. Although deep water corals can form reefs, very little is known about them. Coral reefs are rare along the American and African west coasts. This is due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas (respectively the Peru, Benguela and Canary streams). Corals are seldom found along the coastline of South Asia from the eastern tip of India (Madras) to the Bangladesh and Myanmar borders. They are also rare along the coast around northeastern South America and Bangladesh due to the freshwater release from the Amazon and Ganges Rivers, respectively.

  • The Great Barrier Reef—largest, comprising over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometers (1,600 mi) off Queensland, Australia
  • The Mesoamerican Barrier Reef System—second largest, stretching 1,000 kilometers (620 mi) from Isla Contoy at the tip of the Yucatán Peninsula down to the Bay Islands of Honduras
  • The New Caledonia Barrier Reef—second longest double barrier reef, covering 1,500 kilometers (930 mi)
  • The Andros, Bahamas Barrier Reef—third largest, following the east coast of Andros Island, Bahamas, between Andros and Nassau
  • The Red Sea—includes 6000-year-old fringing reefs located around a 2,000 km (1,240 mi) coastline
  • Pulley Ridge—deepest photosynthetic coral reef, Florida
  • Numerous reefs scattered over the Maldives
  • The Raja Ampat Islands in Indonesia’s West Papua province offer the highest known marine diversity.
 Black CoralAntipathes umbraticaBlack coral. Grand Cayman. Caribbean (Steven Smeltzer)Found from Honduras north to the Bahamas.Black corals (order Antipatharia in the class Anthozoa of the phylum Cnidaria) are important long-lived, habitat forming, sessile benthic suspension feeders.  Dense populations of these corals have been found in both the tropical western Atlantic and southwest Pacific. Many Caribbean reefs harbor large populations of black corals, particularly on the outer reef slopes, where shaded inclined substrata are more likely to be settled by black coral larvae. Black corals are everywhere in the Caribbean, usually at depths below 20 m, but reefs with high levels of suspended particulate matter and seston allow the settlement of black coral larvae as shallow as 5 m.  Antipathes umbratica has branched colonies, low and spreading laterally; usually less than 20 cm high, with thick branches 0.5-1 mm in diameter.  Branches up to 15 cm or more in length; branch angles very wide (usually > 75°); branches spaced varying distances apart (mostly 0.5-1.0 cm). Spines relatively large, triangular, papillose, up to 0.24 mm tall; arranged in 8-10 axial rows. Polyps 0.9 to 1.2 mm in transverse diameter; arranged in a single series, about 0.5 mm apart, with 6-7 polyps per centimeter. Color of living colonies white, light yellow, or reddish brown. Found in caves and under ledges at depths of 25-40 m.
Blushing Star CoralStephanocoenia interseptsBlushing star coral, Grand Cayman, Caribbean (Steven Smeltzer)Found in Caribbean, Bahamas, FloridaThis species forms small to moderately large heads (15-75 cm) and is often simply encrusting. Typically, brownish in color. On approaching this coral, the polyps withdraw giving the colony a blushing appearance.  This species is found in most reef communities, from depths of 1-110
m. The crustos form is the more abundant form of the species in shallower habitats, lagoons, and silty environments (5-15 m), while the boulder form is mostly in fore reef habitats, channels, and deep lagoons, and is more abundant from 10-20 m. The deep-boulder form is often encountered associated with a pinkish-brown polychaete worm.  It has an unusual form of reproduction where fertlised eggs are broadcast from the tentacles of female colonies. Found in a number of reef habitats including channels and lagoons this species of hard coral can grow up to 30cm wide, often in encrusting form. The majority of nutrition is gained from a symbiotic relationship with zooxanthellae. Major threats to this species include white plague type II disease, ocean acidification and coral bleaching caused by elevated sea temperatures.
Common Sea FanGorgonia ventalinaGorgonian Fan on the North Wall, Grand Cayman (Steven Smeltzer)Very widespread from Bermuda south to Curacao.The two large species of this genus, G. ventalina and G. flabellum, are the characteristic and common seafans. They are often difficult to distinguish. Both form a lattice of branches, mostly in one plane which may be orientated across the prevailing current. Both may exceed 1.5 metres tall and wide. The main branches of G. ventalina are usually a fairly strong purple colour. It may have small secondary fans growing off the sides of the main fan. The fine branches of G. ventalina are slightly compressed in the plane of the fan (i.e. flattened on their outer surface), while those of G. flabellum are compressed, usually strongly, at a right angle to the plane of the fan (i.e. on their inner edges). This needs close-up observation to distinguish; otherwise, the presence of side growths on G. flabellum fans, and a slightly more ragged appearance, is the only reasonably consistent way to distinguish between the two species.
Gorgonian – Deepwater Sea FanIciligorgia schrammiDeepwater Sea Fan, North wall 110  feet, Grand Cayman (Steven Smeltzer)Deepwater Sea Fan, Iciligorgia schrammi, Grand Cayman, North side (Steven Smeltzer)Caribbean, Bahamas, FloridaThe Deep Water Sea Fan is a branching, tree-like coral that is a member of the Anthothelidae Family. Branching occurs in pairs in a single plane to create a fan-shaped colony. The outer surfaces of the branches are flat with polyps extending in two parallel rows with narrow inner edges. The Deep Water Sea Fan is predominantly red-brown to orange-brown and found in most deep water environments, from patch reefs to deep slopes, canyons, crevices, and along walls. The Deep Water Sea Fan prefers clean water with some current.
 Gorgonian – Warty Sea RodGorgonia ventalinaWarty Eunicea, soft corals, Grand Cayman.  North side reef (Steven Smeltzer)Common Florida, Bahamas and CaribbeanColony tall, up to 1 m in height and about half as broad; dichotomously branching, not in a single plane. End branches long, up to 17 cm, cylindrical, stout, 8-16 mm in diameter, and uniform in diameter throughout. Calices are low and gaping and occur on small mounds.  E. calyculata is distinguished from all other species of Eunicea by having long, stout branches and a colony not shaped like a candelabrum.
 Graham’s (Dimpled) Sheet CoralAgaricia grahamaeDimpled sheet coral, Grand Cayman (Steven Smeltzer)Dimpled sheet coral, Grand Cayman, North Side (Steven Smeltzer) Found in the Caribbean, the Gulf of Mexico, around Florida and the Bahamas, and along the east coast of South America, to Brazil As its common name suggests, Graham’s sheet coral (Agaricia grahamae) also known as Dimpled sheet coral grows in large, thin plates, which are either flat or slightly curved, and often overlap. Graham’s sheet coral is generally yellowish-brown to grey in colour, usually with pale margins, and, like other corals, its colonies are made up of numerous tiny, anemone-like polyps, which secrete a hard skeleton. In Graham’s sheet coral, the polyps are widely spaced along the bottom of long, roughly concentric depressions (‘valleys’), which are V-shaped in cross-section and are separated by parallel ridges. The underside of the is smooth, lacking polyps. In this species, the individual coral skeletons, known as ‘corallites’, measure around 2 to 2.9 millimetres in diameter. Graham’s sheet coral is similar in appearance to the related Agaricia lamarcki (Lamarck’s sheet coral), but has smaller corallites, more pointed tops to the ridges and lacks the white polyp ‘mouths’ of the latter. It can be distinguished from Agaricia fragilis (fragile saucer coral) mainly by its longer valleys, larger corallites and the smoother appearance of its colonies
Grooved Brain CoralDiploria labyrinthiformisGrooved Brain Coral, Grand Cayman, Caribbean. (Steven Smeltzer)I is found in the Caribbean, the Bahamas, southern Florida, and BermudaA brown or yellow hemispherical-shaped reef-building coral occurring in the Caribbean, the Bahamas, southern Florida, and Bermuda (Humann, 1993). It is most commonly found on offshore reefs at depths between 1 and 30 meters, growing to about 2 meters in diameter (Sterrer, 1986). Bermudian brain corals such as D. labyrinthiformis grow upward at a rate of about 3.5 millimeters per year. Like many other anthozoans, D. labyrinthiformis is host to symbiotic dinoflagellate algae called zooxanthellae. These zooxanthellae are supplied with protection and nutrients from the coral animal, while the coral is supplied with nutrients and energy for calcification and growth.  It is identified by its characteristically brain-like hemispherical-shaped heads, and deep, interconnected polyp-bearing valleys which are separated by broad, grooved ridges. Coloring ranges from varying degrees of yellow and brown, and growth can reach up to about 2 meters in diameter. Like other scleractinian species, D. labyrinthiformis is a sessile animal, with the only locomotion involved in its life cycle found in its planktonic larval stage. Because of its strictly benthic behavior, the colonial D. labyrinthiformis polyps depend mostly on suspension feeding methods to obtain nourishment. By using their tentacles and extruded mesenterial filaments, the polyps prey primarily on zooplankton and bacteria. The polyps are equipped with nematocysts that, when triggered, immobilize and hold prey. Mucus and cilia then aid in the capture and transport of these food particles to the mouth.
Lamrack’s Sheet CoralAgaricia lamarckiLamarck's sheet coral at 90 feet off the east wall in Grand Cayman (Steven Smeltzer)Occasional in Florida and the Bahamas, common in the Caribbean.Colonies form large, mostly thick plates, broad, rounded or acute, often overlapping each other. The upper surface bears concentric rows of ridges with relatively wide, straight or reticulate, valleys. The white, star-like, polyps are in the valleys’ center. The septa alternate in height and thickness. Generally, the taller and thicker primary septa extend close to the columella before dropping sharply into the corallite pit, while the thinner secondary septa appear shorter, because they slope gradually into the corallite pit. The underside of the colony is smooth, without polyps. Yellow-brown to golden-brown to brown, sometimes with bluish or grayish tints, with contrasting white polyps. Corallite diameter 3.1-4.5 mm, with 20-32 septa per corallite; septa alternate in height and thickness. Columella present, trabecular and discontinuous. On sloping reefs and along walls, between 5 and 50 m, but most common between 20 and 35 m.
Rough Sea PlumeMuriceopsis flavidaSoft Corals, Grand Cayman, Pseudopterogorgia americana, North Wall (Steven Smeltzer)On Deck, Oro Verde shipwreck, Grand Cayman (Steven Smeltzer)Common Florida, Bahamas and CaribbeanColonies form bushy clusters of tall, plume-like branches, up to 75 cm in height. Several long main branches give rise to numerous shorter branchlets, 5-8 cm in length. The slender branchlets, 2.5 mm in diameter, extend from all sides of the main branches. Often, secondary branches develop new plumes from the main branch. Very small, less than 1 mm, closely set apertures occur on all sides of the main branches and branchlets. The apertures have small, lower shelf-like lips, giving the surface a somewhat rough texture. There is regional variation in coloration: specimens from the Caribbean are dull brown or buff-white, while specimens from other parts of the West Indies are purple tinged with yellow.
Soft Coral GardenSoft CoralsCoral garden, slit-pore sea rods, sponges, hard coral, star coral, Grand Cayman (Steven Smeltzer)
Soft Corals, Grand Cayman, Pseudopterogorgia acerosa, Near Babylon (Steven Smeltzer)
Coral reefs are estimated to cover 284,300 square kilometers (109,800 sq mi), just under one tenth of one percent of the oceans’ surface area. The Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) account for 91.9% of this total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs account for 7.6%.  Although corals exist both in temperate and tropical waters, shallow-water reefs form only in a zone extending from 30° N to 30° S of the equator. Tropical corals do not grow at depths of over 50 meters (160 ft). The optimum temperature for most coral reefs is 26–27 °C (79–81 °F), and few reefs exist in waters below 18 °C (64 °F). However, reefs in the Persian Gulf have adapted to temperatures of 13 °C (55 °F) in winter and 38 °C (110
°F) in summer.
Soft corals look like colorful plants or graceful trees and are not reef-building since they do not produce the hard calcified skeleton of many reef-building corals. However, soft corals do produce smaller amounts of calcium carbonate that help them keep their shape. Soft corals can be distinguished from hard corals by the fact that soft coral polyps always have eight tentacles, while hard coral polyps have multiples of six tentacles.  Hard corals, also called reef-building corals, produce a rock-like skeleton made of the same material as classroom chalk (calcium carbonate). These skeletons and the various shapes of different colonies form the familiar structure of the reef. Hard corals rely on symbiotic algae (zooxanthellae) living within their tissues for nutrition and energy to build their skeleton. They must therefore live in shallow clear water to allow sunlight to reach the algae.  Coral reefs are among the most biologically diverse ecosystems on earth. Second only to tropical rain forests in the number of species they harbor, they are sometimes called the “rainforests of the sea”. Although coral reefs only occupy about 0.07 percent of the ocean floor (an area roughly the size of Texas), they are home to as many as one quarter of the world’s marine species. Coral reefs offer important income sources for their human neighbors through tourism and fishing, which provide both subsistence and trade. Recently, scientists have begun to discover that coral communities may contain valuable medicines that may one day lead to treatments for cancer and HIV. For coastal communities, coral reefs also play an important role in protecting their coastlines from storms.