14 DAY TRIAL // Corals really give a meaning to the notion that beauty is under the surface. That's the clearest seawater, a crystal clearness increased by the white sand. A coral reef is like a sea rainforest.
Corals are colonies of polyps, small animals with a maximum diameter of 2.5 cm (1 in). The soft polyp is connected to its neighbor through living tissue covered by mucus. During the day, the corals seem to be dead stones, because the polyps retire into their skeletons. During the night, the spread tentacles of the polyps swing gently, giving the reef a soft, fluffy look. The stony "tree" in which the polyps live is a combination of their skeletons, cemented by calcium carbonate (limestone), extracted from the seawater.
There are about 800 species of reef making corals, amazing through shapes, sizes and colors. The coral branches may take various shapes, from moose or deer antlers, to trees, columns, tables, umbrella, mushrooms, as their names suggest. There are also lattice, carnation, strawberry and even brain corals (Meandrina).
The 'jungle' of the coral reef harbors a quarter of the species found in the seas and oceans, from microscopic animals and algae to sea lilies, octopuses, sponges, shrimps, lobsters, snails, starfishes, rays, sharks, moray eels and turtles. Only rainforests are more diverse: reefs harbor the highest marine biodiversity, thus the highest number of fish species: thousands of species in the worldwide reefs.
There are fish groups restricted to corals, many weird shaped or extremely colorful, including damselfishes and clownfishes (Pomacentridae), Moorish idols (Zanclus), trumpetfishes (Aulostomus), triggerfishes (family Balistidae), which have evolved an original defense system linked to life in the reef: three spines, which when fixed into the coral, a predator must break the coral to get to them; the surgeonfish (family Acanthuridae) with sharp caudal spines, real scalpels, on each side of the tail; the filefishes (family Monacanthidae) with abrasive skin; lionfish or turkeyfish (also known as firefish or scorpionfish) (Pterois genus) with long venomous spines; the stonefish (family Synanceiidae) perhaps the most dangerous fish of the reef, as they possess the most powerful venom amongst all fish species, an extremely toxic neurotoxin, which is deadly to humans and mimic rocks by color and form; the batfishes (family Ogcocephalidae) which look like tadpoles and can walk on the bottom of the ocean in a toad like style; the porcupinefishes (the family Diodontidae) with well-developed sharp spines covering the body and which can inflate their body (by swallowing water or air); the butterflyfishes (of the genus Chaetodon) with a spot imitating an eye at the base of their tail; the boxfishes (cowfishes, family Ostracionides) with the body enclosed in a bony carapace with a honeycomb model.
This fish diversity is possible because fish have different feeding programs. Some eat in the morning or evening, others during the night. Because of this, smaller fish have their hours when they can eat in calm, without being stressed by predators. And the reef fish are very picky: for example, the spotted coralgrouper (Plectopromus maculatus) prefers sea goldies (Pseudanthias squammipinnis).
Coral fish are extremely colorful, but why? Many are venomous and signal this through vivid colors, like the lionfish. Other have deceptive models: the tail of the butterflyfish mimics the head, having even fake eye models. Many coral fish use colors as signals. When the coral hind (Cephalopholis miniata) starts hunting, its color changes. This is important, as this way sanitary fish, which pick parasites from its body, know when it is safe to approach. When an anemonefish, which is hunted by the hind, knows the predator is on its spare time, it will chase it away with all the courage out of its territory.
Coral reefs are the home for world's largest clams, Tridacna, which can have 227 kilograms (500 pounds) and measure up to 1.2 m (4 ft) across, living at least 100 years.
A coral can weigh a few tones and raise 9 m (30 ft) over the sea bottom. Coral reefs grow only in tropical seas, no deeper than 60 m (200 ft). The reefs require an environment poor in nutrients, explaining the clear water in a reef. The barrier-reef of Tahiti, for example, grows with 6 mm per year.
The coral reefs form the largest biological structures on Earth. The largest coral structure in the world is the Great Coral Barrier of northeastern Australia, located in the Coral Sea: it is 2,010 km (1,200 mi) long and 2 to 150 km (1.2-92 mi) wide, covering the surface of England and Scotland united. It is also the most biodiverse reef in the world. Only in an islet, researchers found 100 species of corals, 700 of fish (imagine this is five times more than the number of fish species encountered in the European rivers!), 25 species of sea cucumber, 34 species of cone-shelled snails. This without mentioning the sea turtles and sea birds.
The second reef in the world is the Belize Coral Barrier. It is the longest reef in the western hemisphere, 300 km (190 mi), parallel with the shore of the Yucatan peninsula (Belize and southeastern Mexico), comprising 450 coral islets and 3 atolls. It has a surface of 960 square km. It contains 70 species of reef making corals, 500 species of fish, endangered sea turtles, manatees, and American crocodiles.
Bird's Head Seascape, of northwestern New Guinea, covers 18 million hectares, and it is home to more than 1,200 species of fish and almost 600 species of reef-building coral (75 % of the world's known total).
Australia's Great Barrier Reef, covering an area 10 times bigger, has more types of fish - 1,464 species - but just 405 species of coral. And the bigger Caribbean Sea has fewer than 1,000 species of fish and just 58 types of coral. In the Red Sea, one square meter of coral can contain 20 species of coral.
The polyps hunt small animals with their tentacles, but they also live in symbiosis with algae called zooxanthellae that make photosynthesis, that's why the corals live only in lighted places. The photosynthesis products of the algae are eaten by the polyps, and their waste products are used by the algae to synthesize biochemical compounds. The healthy coral is brown, green, red, blue or yellow. The symbiosis with the algae allows the corals to live in tropical nutrient-poor waters.
As they need light, current and warm waters, between the coral species there is a strong competition for space. Even if corals live fixed to the sea bottom, between two colonies that live very close to one another sometimes fierce "battles" can be triggered for space and food supply. The species is named the fire coral (Millepora alcicornis), an extremely aggressive one living in calm waters under a depth of 10 m (33 ft); if it detects the presence of another coral in a range of 30 cm (1 ft) around, it will kill it.
Special ramifications, which have an odd hand shape, travel centimeter by centimeter, in a few months, the distance to the neighboring colony, sneak amongst its branches, fix on them and suffocate them. The offensive coral does not touch algae, sponges or other Millepora. The fire coral attacks especially the splendid Gorgonia species, with a varied color pattern. The aggressor attacks only if its "rival" is placed upstream to the current.
Specialists believe Gorgonia releases a chemical, which by the water current is detected by Millepora that develops faster on an already built coral skeleton.
The fire corals are the most dangerous for scuba divers, as in contact with the human skin they provoke an intense, even if short pain, but also reddening hives and itches. Defensive cells, called nematocysts that go off, penetrate the skin with some microscopic harpoons which inject venom. If the contact is made with a smaller animal, this can be paralyzed or killed.
The way corals breed is amazing. The light of the silvery moon induces such an arousal amongst corals that soon the sea water gets flooded by coral eggs and sperms that turn the water milky.
The corals can make a perfect synchronization with moon's phases, increasing their chances for fertilization.
Corals have no eyes (even if jellyfish, their relatives, do have some extremely primitive "eyes"), but hundreds of species of corals are still able to detect changes in light, especially blue light, and to react to them, because of proteins named cryptochromes, which are sensitive to light. Cryptochromes are also encountered in mammals and insects, being responsible for the control of the circadian clock that tunes the daily rhythms.
Biologically, the reefs are considered the most productive underwater ecosystems. Reefs also form a barrier between the waves and the shore and form foundation for thousands of tropical islands.
Still, corals are very fragile. They can be broken off by hand. You can imagine the effect of ships chocking to corals, or anchoring on a coral area. But, the greatest danger is posed by chemical contamination, oil spill, wastes, sediments and infiltration of freshwater. In developing countries, residual waters are drained into the sea without any treatment. Farm fertilizers reaching the sea increase the amount of organic matter in the sea and kill the corals; so does the fish farming, too. Also, deforestation and mining degrade reef waters.
Reefs are destroyed with dynamite (for fishing) and mined. In southeastern Asia, fishermen use a cyanide solution for stunning the fish to capture them easier. The fish can still be eaten, as they expel the venom, but the venom remains in the water, provoking the death of the reefs. In Sri Lanka and India, whole portions of the reef have been covered in cement. Ships also destroy many reefs through anchoring or contact. Plastics, aluminium cans, fishing hooks and glass bottles are indestructible, polluting the reef for long.
When stressed, the corals spit out the algae (which are immediately eaten by the fish) and if the process persists, coral death (bleaching) installs. Today, bleaching is extended worldwide and fish and other species are gone. Coral bleaching used to be periodic and isolated. Now, it has planetary proportions.
Over 10 % of the world's reefs have already been destroyed. By 2030, 70 % of the world's reefs could be gone in 93 countries. Only remote reefs are really healthy. Destroyed reefs are encountered in Japan, Taiwan, Philippines, Indonesia, Singapore, Sri Lanka, India, Kenya, Tanzania, Mozambique, Madagascar, Haiti, Cuba, Florida, Jamaica, Trinidad, Tobago. Overcrowding and development in those areas spurred the phenomenon.
In 1983, 95 % of the corals of the Pacific coast of Central America died. A less powerful bleaching occurred in central/western Pacific, Great Coral Barrier, Thailand, Galapagos, Bahamas, Columbia, Jamaica, Texas and Puerto Rico.
Some link the coral death to the thinning of the ozone layer, as corals would be somehow sensitive to ultraviolet light. Also, CFC that destroys the ozone layer is not only going to persist for 100 years, but it is 20,000 times more powerful than carbon dioxide in inducing the greenhouse effect.
Hurricane Mitch destroyed about 48 % of the Belize reefs, in 1997-1998.
Corals breed between 25 to 29 oC, but 1-2 oC over these values can be deadly. Global warming seems to pose a great threat for the corals. If global warming means a temperature rise of 3-8 oC in the atmosphere, this will be the doom the corals. Paradoxically, the corals' disappearance will increase global warming, as they consume a lot of carbon dioxide for building the calcium carbonate skeletons and their deterioration will speed up the process that destroys them.
