November 03, 2007

Coral reefs form an unusual, endangered and ecologically important ecosystem in the oceans. They are the ‘Rainforests’ of the ocean and have a high biodiversity that serves as a storage bank of rich genetic resources such as sponges, nudibranchs, fish (like Blacktip Reef Sharks, groupers, clown fish, eels, parrotfish, snapper, and scorpion fish), jellyfish, anemones, sea stars (including the destructive Crown of Thorns), crustaceans (like crabs, shrimp, and lobsters), turtles, sea snakes, snails, and mollusks (like octopuses, nautilus, and clams). Birds also feast on coral reef animals. They protect the coast from wave erosion.

How are coral reefs formed?

The reef’s massive structure is formed from coral polyps, tiny animals that live in colonies. In most reefs, the predominant organisms are stony corals, colonial cnidarians that secrete an exoskeleton of calcium carbonate (limestone). The accumulation of skeletal material, broken and piled up by wave action and bioeroders, produces a massive calcareous formation that supports the living corals and a great variety of other animal and plant life.

Most corals feed at night. To capture their food, corals use stinging cells called nematocysts. These cells are located in the coral polyp’s tentacles and outer tissues. If you’ve ever been “stung”

by a jellyfish, you’ve encountered nematocysts of an animal of phylum cnidaria.

Types of corals

There are two types of coral, hard coral and soft coral. Hard corals (like brain coral and elkhorn coral) have hard, limestone skeletons which form the basis of coral reefs. Soft corals (like sea fingers and sea whips) do not build reefs.

Types of reefs

Reef can take variety of formations some of them are:

Fringing reefs are reefs that form along a coastline. They grow on the continental shelf in shallow water.

Barrier reefs grow parallel to shorelines, but farther out, usually separated from the land by a deep lagoon. They are called barrier reefs because they form a barrier between the lagoon and the seas, impeding navigation.

Coral Atolls are rings of coral that grow on top of old, sunken volcanoes in the ocean. They begin as fringe reefs surrounding a volcanic island; then, as the volcano sinks, the reef continues to grow, and eventually only the reef remains.

Apron reefs are short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.

Ribbon reefs are long, narrow, somewhat winding reef, usually associated with an atoll lagoon.

Table reefs are isolated reefs, approaching an atoll type, but without a lagoon.

Where are coral reefs found?

Coral reefs develop in shallow, warm water, usually near land, and mostly in the tropics; coral prefer temperatures between 21 and 30 degree Centigrade.

Coral reefs are estimated to cover 284,300 square kilometres. There are two distinct regions in which coral reefs are primarily distributed: the Wider Caribbean (Atlantic Ocean) and the Indo-Pacific (from East Africa and the Red Sea to the Central Pacific Ocean).

The diversity of coral is far greater in the Indo-Pacific, particularly around Indonesia, the Philippines, and Papua New Guinea. Many other groups of marine fauna show similar patterns, with a much greater diversity in the Indo-Pacific region.

Although they possess a smaller number of species the corals of the Atlantic are still unique, with few common species between the two regions. The Atlantic and Caribbean account for 7.6 per cent of the total world reef.

Coral reefs are found in about 100 countries. They are home to over 25 per cent of all marine life and are among the world’s most fragile and endangered ecosystems. In the last few decades over 35 million acres of coral reefs have been obliterated. Reefs of 93 countries have been damaged.

Famous coral reefs and reef areas of the world include:

The Great Barrier Reef — largest coral reef system in the world, Queensland, Australia

The Belize Barrier Reef — second largest in the world, Belize, Central America

The Red Sea Coral Reef — located off the coast of Egypt and Saudi Arabia.

Pulley Ridge — deepest photosynthetic coral reef, Florida

Many of the numerous reefs are found scattered over the Maldives.

Threats to coral reefs

Human activities remain the single greatest threat to the reefs all over the world. Some are discussed below.

Sedimentation — Construction along coasts, mining, farming and logging of rainforests cause soil smothering which blocks sunlight that coral reefs need to survive.

Destruction of forests — Mangrove forests along the coast used to absorb massive amounts of nutrients and sediment from runoff caused by farming and construction of roads, buildings, ports, channels, and harbours. They are now being destroyed. Coral reefs are biological assemblages adapted to waters with low nutrient content, and the addition of nutrients favours species that disrupt the balance of the reef communities. Both the loss of wetlands and mangrove habitats are considered to be significant factors affecting water quality on inshore reefs.

Fishing with explosives — In depleted fisheries, people resort to desperate tactics to catch the fish — one of them is dynamite. The explosions send dead fish to the surface and destroy living reefs. Areas that used to be full of coral become deserts, full of coral rubble, dead fish and little else after dynamite fishing.

Water pollution — Petroleum products and chemicals are lethal to coral reefs. Raw sewage is dumped into the sea, bringing an overload of nutrients; algae take over the reefs, blotting out the sunlight corals need to live. Poor water quality has also been shown to encourage the spread of infectious diseases among corals. Copper, a common industrial pollutant, has been shown to interfere with the life history and development of coral polyps.

Careless recreation and collection of coral — Careless boating, diving and fishing can cause damage to coral reefs.

Ocean acidification — Increased amount of carbon dioxide in the atmosphere is increasing the amount of carbon dioxide dissolved in the ocean, as a result increasing its pH. Carbon dioxide gas dissolved in the ocean reacts with water to form carbonic acid, resulting in ocean acidification. Ocean surface pH is estimated to have decreased from approximately 8.25 to 8.14 since the beginning of the industrial era, and it is estimated that it will drop by a further 0.3 - 0.4 units by 2100 as the ocean absorbs more anthropogenic (human produced) CO2. increased pH causes the desolution of the calcium carbonate.

Global warming — Corals cannot survive in very high temperatures. When ocean temperatures increase, the coral polyps lose the symbiotic algae inside them, causing them to turn white and die. This is referred to as “bleaching”. During the past year there has been an unprecedented number of “bleaching” events worldwide.

If the present rate of destruction continues, 70 per cent of the world’s coral reefs will be destroyed within the next few decades.

Climate change will destroy the world’s great coral reefs within a century, according to a report by German and Australian marine scientists. A slight rise in maximum water temperatures — only one to two degrees — can stress the corals. This causes them to expel the microscopic organisms, known as zooxanthellae, which colour their tissues and provide them with essential nutrients. If the zooxanthellae don’t return, the corals will die.

In 1998, the warmest year on record, every reef system in the world’s tropical oceans was affected by some degree of bleaching. A report published in 2006 on coral reef and bleaching says the frequency and intensity of bleaching is set to rise. The report warned that coral reefs could be eliminated from most areas of the world by 2100; even the world’s largest reef — the Great Barrier Reef of Australia — could be dead within 30 years unless measures are taken now to slow climate change.

General estimates show approximately 10 per cent of the coral reefs around the world are already dead. The beautiful invertbrates have to be preserved. They are the home of variety of animals. If they die, several marine species will be removed from the face of the earth forever.