According to a new study commissioned by the European Commission, chemical sunscreens bleaching pose a threat to coral reefs destruction.These chemical sunscreens are putting coral reef in danger by the bleach pollution they create, in turn affecting the coral reef food chain.
TUNGSHA, Taiwan -- Chinese fishermen have been accused of poaching in Taiwan's first marine national park where authorities here say their destructive methods are endangering the area's ecology.
Last week, scientists issued their latest, grim assessment of the world's coral reefs. But as Steve Connor reports from Florida, extraordinary new ocean 'reseeding' techniques mean there may still be time to halt – or even reverse – the destruction of mother nature's marine marvels
Climate change, water pollution, destructive fishing and damage to coastal habitats are all contributing factors, according to the first global scientific assessment of reef-building coral.
A survey of 704 species of coral, tiny polyps with hard shells, some of which form spectacular underwater reefs, has found that nearly 33% of them face a greater threat of becoming extinct as the globe warms. If the reefs go, it won't just be corals that disappear from the world's oceans
One third of the major reef-building coral species are vulnerable to extinction, and the pace of destruction is increasing so it is conceivable that the "rainforests of the ocean" could be wiped out this century.
Stresses such as rising seawater temperatures, destructive fishing practices, shipwrecks, and increases in the amount of sediment, and contaminants running off land and into coastal waters are making life hard on stony corals. Ten percent of corals are so degraded that scientists do not expect them to recover.
Coral reefs are aragonite structures produced by living organisms, found in marine waters containing few nutrients. In most reefs, the predominant organisms are stony corals, colonial cnidarians that secrete an exoskeleton of calcium carbonate. The accumulation of skeletal material, broken and piled up by wave action and bioeroders, produces a calcareous formation that supports the living corals and a great variety of other animal and plant life.
Coral reefs most commonly live in tropical waters, but deep water and cold water corals exist on a much smaller scale.
Globally, coral reefs are under threat from climate change, ocean acidification, overuse of reef resources, and harmful land-use practices. High nutrient levels such as those found in runoff from agricultural areas can harm reefs by encouraging excess algae growth.
Formations
Coral reefs can take a variety of forms, defined in following:
- Fringing reef – a reef that is directly attached to a shore or borders it with an intervening shallow channel or lagoon.
- Barrier reef – a reef separated from a mainland or island shore by a deep lagoon ( see Great Barrier Reef ).
- Patch reef – an isolated, often circular reef, usually within a lagoon or embayment.
- Apron reef – a short reef resembling a fringing reef, but more sloped; extending out and downward from a point or peninsular shore.
- Bank reef – a linear or semi-circular shaped-outline, larger than a patch reef.
- Ribbon reef – a long, narrow, somewhat winding reef, usually associated with an atoll lagoon.
- Atoll reef – a more or less circular or continuous barrier reef extending all the way around a lagoon without a central island.
- Table reef – an isolated reef, approaching an atoll type, but without a lagoon.
Distribution
Coral reefs are estimated to cover 284,300 square kilometres, with the Indo-Pacific region (including the Red Sea, Indian Ocean, Southeast Asia and the Pacific) accounting for 91.9% of the total. Southeast Asia accounts for 32.3% of that figure, while the Pacific including Australia accounts for 40.8%. Atlantic and Caribbean coral reefs only account for 7.6%.
Coral reefs are rare on Americas west coast, as well as Africa west coast. This is due primarily to upwelling and strong cold coastal currents that reduce water temperatures in these areas. Corals are seldom found along the coastline of South Asia from Pakistan to Bangladesh. They are also rare along the coast around north-eastern South America and Bangladesh due to the freshwater release from the Amazon and Ganges Rivers respectively.
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 m (165 ft). Temperature has less of an effect on the distribution of tropical coral, but it is generally accepted that they do not exist in waters below 18 °C., and that the optimum temperature is 26-27° Celsius for most coral reefs. The reefs in the Persian gulf however have adapted to temperatures of 13° Celsius in winter and 38° Celsius in summer. deep water coral is more still exceptional since it can exist at greater depths and colder temperatures. Although deep water corals can form reefs, very little is known about them.
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, stretching from southern Quintana Roo, Mexico along the coast of Belize to the Bay Islands of Honduras.
- The New Caledonia Barrier Reef - second longest double barrier reef in the world, with a length of about 1500 km.
- The Andros, Bahamas Barrier Reef - third largest in the world, following the east coast of Andros Island, Bahamas, between Andros and Nassau.
- The Red Sea Coral Reef - located off the coast of Israel, Egypt and Saudi Arabia.
- Pulley Ridge - deepest photosynthetic coral reef, Florida
- Numerous reefs scattered over the Maldives
- Ghe Raja Ampat Islands in Indonesia's West Papua province offer the highest known marine diversity.
Biology
See also: CoralCoral consists of accumulations of individual organisms called polyps, arranged in diverse shapes. Reefs grow as polyps along with other organisms deposit calcium carbonate, the basis of coral, as a skeletal structure beneath and around themselves, pushing the coral's "head" or polyps upwards and outwards. Waves, grazing fish (such as parrotfish), sea urchins, sponges, and other forces and organisms break down coral skeletons into fragments that settle into spaces in the reef structure. Many other organisms living in the reef community contribute skeletal calcium carbonate in the same manner. Coralline algae are important contributors to reef structure in those parts of the reef subjected to the greatest forces by waves (such as the reef front facing the open ocean). These algae deposit limestone in sheets over the reef surface, thereby strengthening it.
Reef-building or hermatypic corals are only found in the photic zone (above 50 m depth), the depth to which sufficient sunlight penetrates the water for photosynthesis to occur. Coral polyps do not photosynthesize, but have a symbiotic relationship with single-celled organisms called zooxanthellae; these cells within the tissues of the coral polyps carry out photosynthesis and produce excess organic nutrients that are then used by the coral polyps. Because of this relationship, coral reefs grow much faster in clear water, which admits more sunlight. Indeed, the relationship is responsible for coral reefs in the sense that without their symbionts, coral growth would be too slow for the corals to form impressive reef structures. Corals get up to 90% of their nutrients from their zooxanthellae symbionts.
Corals can reproduce both sexually and asexually. An individual polyp may use both reproductive modes within its lifetime. Corals reproduce sexually by either internal or external fertilization. The reproductive cells are found on the mesentery membranes that radiate inward from the layer of tissue that lines the stomach cavity. Some mature adult corals are hermaphroditic; others are exclusively male or female. A few even change sex as they grow.
Internally fertilized eggs develop in the polyp for a period ranging from days to weeks. Subsequent development produces a tiny larva, known as a planula. Externally fertilized eggs develop during synchronized spawning. Polyps release eggs and sperm into the water simultaneously. Eggs disperse over a large area. Spawning depends on four factors: time of year, water temperature, and tidal and lunar cycles. Spawning is most successful when there is little variation between high and low tides. The less water movement, the better the chance for fertilization. Ideal timing occurs in the spring. Release of eggs or planula larvae usually occurs at night and is sometimes in phase with the lunar cycle (3–6 days after a full moon). The period from release to settlement lasts only a few days, but some planulae can survive afloat for several weeks (7, 14). They are vulnerable to heavy predation and adverse environmental conditions. For the lucky few who survive to attach to substrate, the challenge comes from competition for food and space.
Ecology and biodiversity
Coral reefs support extraordinary biodiversity although they are located in nutrient-poor waters. The process of nutrient cycling between corals, zooxanthellae, and other reef organisms explains why reefs flourish in these waters: recycling ensures that fewer nutrients are needed overall to support the community.
Cyanobacteria provide soluble nitrates for the reef via nitrogen fixation. Corals absorb nutrients, including inorganic nitrogen and phosphorus, directly from the water, and they feed upon zooplankton that pass the polyps via water motion. Thus, primary productivity on a coral reef is very high, which results
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