Scientists predict that 70 per cent of the world’s coral reefs may well be destroyed over the next 20-40 years, unless we stop cyanide fishing, pollution, sewage, erosion and clumsy tourism.
Coral reefs are one of the most diverse ecosystems on our planet, rivalling that of the tropical rainforest. They have been built over thousands of years (some of the oldest reefs began growing about 25 million years ago) by tiny calcium-producing organisms, and are a haven for thousands of life forms. The coral reefs are unique in that living examples from nearly every group of organisms, representing a billion years of evolution, can be found there. In spite of this, we have spent less time exploring the world’s oceans than we have the surface of the moon.
Corals are classified as Cnidaria. They share the class Anthozoa with sea anemones, sea pens and sea pansies. Of the 6,000 known anthozoan species, 2,500 are corals. Corals are found in all oceans of the world, from the tropics to polar regions, to depths of 6,000m (19,700ft).
Reef-building corals are generally found at depths of less than 46m (150ft), where sunlight penetrates. These corals have a symbiotic relationship with algae and need sunlight to grow and thrive. Clear water, where light reaches the algae that promote polyp calcification, speeds growth. Reef-building corals require warm ocean temperatures of 20-28 degrees centigrade.
Warm water flows along the Eastern shores of major land masses and reef development is generally more abundant in areas that are subject to strong wave action. Waves carry nutrients and oxygen to the reef as well as distributing coral larvae and preventing harmful sediments from settling on the reef. Precipitation of calcium from the water is necessary to form a coral polyp’s skeleton. This precipitation occurs when water temperature and salinity are high and carbon dioxide concentrations are low, conditions typical of shallow, warm tropical waters.
Types of coral reef
Fringing reefs - which border the coast closely
Barrier reefs - which are separated from the land by a lagoon
Atolls - which develop at or near the surface of the sea when islands that are surrounded by reefs subside.
Feeding
Reef building corals rely on the photosynthetic products of algae. They also eat zooplankton which they capture with their tentacles and trap in mucus. They feed mostly at night.
Reproduction
Both sexual and asexual - by budding, fragmentation and mass spawning. The resulting zygotes develop into larvae which attach themselves to a suitable substrate. Some species brood their larvae, the sperm fertilises the eggs before they are released and they float to the top, settle and become another colony.
Conservation
Coral reefs cover less than 0.2 per cent of the ocean floor, but contain approximately 25 per cent of the ocean’s species. Almost 5,000 species of reef fish have been identified as well as more than 2,500 species of coral itself, of which almost 1,000 are reef-building. The calcium carbonate from sand, shells and coral maintains the pH balance in the ocean, which in turn maintains life within it.
What corals do for us
Corals provide shore lines with protection by breaking up wave action. They serve as nurseries for growing fish and give food, shelter and protection to a variety of marine species. They supply a protein source to the diets of coastal peoples and provide jobs through fishing and tourism. Corals provide a good source of medicine against a variety of illnesses and give us a wondrous underwater world to study and enjoy.
What we do for corals
In return, we pollute them with sewage, fertilisers and pesticides. We fish them in destructive ways through overfishing, chemicals and use of damaging equipment. We mine them with explosives and they can become smothered by the silt resulting from logging, increasing land use and development. We anchor and ground boats on them, step on them, drag dive gear over them and chop them down for jewelery and coffee table curios.
-BBC-Science & Nature
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