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Vol 8,  No 6  August 15, 1999
Preparing you to change the future every fortnight


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Corals are to the oceans what tropical rainforests are to land. Known as Neptune’s goblets, they are a vital link in the marine ecosystem and, in fact, store more biodiversity than the rainforests. But human activity is gobbling them up. And global warming is making matters worse. Bleaching and coral disease outbreaks are increasing in frequency, intensity and range. And reefs in the Indian Ocean are said to be the worst-affected. Are corals dying to tell us something?

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Losing colour
From Central America to Australia, from the 2,000-km Great Barrier Reef to the small, reefs in Pacific islets, bleaching takes the life out of corals the world over

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bul_red.gif (868 bytes)MRIDULA CHETTRI
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Corals, the rainforests of the oceans, are dying. Victims of global warming, scientists say 10 per cent of the Earth’s coral reefs have been reduced to skeletons, another 30 per cent are in a critical condition and a further 30 are under severe en     vironmental stress. "By the year 2050 they could all be dead," says Clive Wilkinson of the Global Coral Reef Monitoring Network (GCRMN), Townsville, Australia. "If the projected levels of climate change are not stopped, the doom may be just 30 years away," warns the United Nations’ Inter-Governmental Panel on Climate Change (IPCC).

The IPCC projects coral reefs to be among the most sensitive ecosystems to long-term climate change. They are small animals, mostly living in vast colonies, harvesting nourishment and energy from microscopic algae (plants called zooxanthellae), which inhabit their cells by the thousands. The algae are golden brown in colour and combine with other pigments to lend their coral hosts, which largely have transparent tissues, a spectacular hue. When  environmentally-stressed, corals lose much of their algae. In this state, corals appear white and are referred to as "bleached".

Coral bleaching was reported in at least 60 countries and island nations in 1998 (see map: Far and wide). "Reports by experienced observers are of unprecedented bleaching in places as far apart as the West Asia, East Africa, the Indian Ocean, South, Southeast and East Asia, the far West and far East Pacific, the Caribbean’s and the Atlantic Ocean," says Wilkinson. Only the Central Pacific region seems to have been spared.

Coral reefs have suffered the most damage in heavily-populated coastal areas, largely in developing countries

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Preliminary assessments indicate that the Indian Ocean is the most severely impacted region. More than 70 per cent mortality has been observed off the coasts of Kenya, the Maldives, the Andamans and the Lakshwadweep islands. And about 75 per cent of the corals have been reported to be dead in the Seychelles Marine Park System and the Mafia Marine Plant off Tanzania, says Wilkinson.

The first report of coral bleaching came nearly 80 years ago. However, at that time Alfred Mayer, an oceanographer, dismissed it as a natural event because the events   were localised, rare and the corals recovered soon after. It was only in the mid-1980s that coral reefs around the world  began to experience large-scale bleaching frequently. However, the coral bleaching of 1998 is the most catastrophic and geographically extensive in recorded history, says Wilkinson. Moreover, unlike previous bleaching episodes, which were most severe at depths of 15 metres, the impact of the 1998 coral destruction extended to as much as 50 metres deep, he says.

Wilkinson points out four overlapping levels of bleaching:

dot.gif (88 bytes) catastrophic: with massive mortality (often affecting near 95 per cent of shallow corals) in Bahrain, the Maldives, Sri Lanka, Singapore and in large areas of Tanzania;

dot.gif (88 bytes) severe: with around 50-70 per cent mortality and with some coral recovery in Kenya, Seychelles, Japan, Thailand, Vietnam, and Belize;

dot.gif (88 bytes) moderate and patchy: on some reefs in large areas, with a mix of coral recovery and around 20-50 per cent mortality but no ill-effects in other parts, such as in Oman, Madagascar, the inner Great Barrier Reef, parts of Indonesia and the Philippines, Taiwan, Palau, French Polynesia, the Galapagos, the Bahamas, Florida, the Cayman Islands, Bermuda, and Brazil;

dot.gif (88 bytes) insignificant or no bleaching: in large areas of the world’s reefs such as the Red Sea, the southern Indian Ocean, the Andaman Sea, most of Indonesia, large parts of the Great Barrier Reef, most of the central Pacific and parts of the
southern and eastern Caribbean.

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Encyclopaedia Britannica
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Encyclopaedia Britannica
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Encyclopaedia Britannica
Dyed white: when corals lose algae , a source of nutrition and colour, from their tissues they appear white, a condition known as bleaching (above left). Global warming has been blamed for the extensive bleaching of corals in 1998. It is also said to make corals susceptible to disease, which have increased dramatically in recent years, both in terms of outbreaks and emergence of new ones. Some of them are black band disease (above) and white pox

However, recent reports indicate that the Indian reefs, too, have not been left untouched. Bleaching has been reported in several areas along the reefs spread over Andaman and Nicobar Islands, Lakshwadweep, Gulf of Kutch and Gulf of Mannar. Corals that were abundant in the lagoons of the Lakshwadweep and Andaman and Nicobar Islands are getting destroyed (see box: Indian shores).

Widespread bleaching of corals has been reported in the Andaman and Nicobar Islands

India has an estimated 18,000 square kilometres of coral reefs, mainly located around the Lakshwadweep and the Andaman and Nicobar Islands. The Gulf of Kutch and the Gulf of Mannar also have small stretches of coral reefs. But all’s not well with the underwater paradise in these areas.

A study by Port Blair-based Society for Andaman and Nicobar Ecology (SANE), a non-governmental organisation, reported widespread bleaching of corals on the Andaman and Nicobar coast. R Soundararajan of SANE and his team members noticed this "mass bleaching" phenomenon in the coral reefs throughout the length and breadth of the islands in early May 1998. The study of five sites along a 40-km stretch around the islands found almost 100 per cent bleaching in the Andaman reefs and 30 to 70 per cent in Nicobar. The Andaman Sea was 2°C warmer than normal, notes the study, which was sponsored by the World Wide Fund for Nature under its Biodiversity Hotspots Conservation Programme. It has also noted that the mortality of giant clams, an associated faunal species of coral reefs, had touched alarming levels.

Meanwhile, scientists at the National Institute of Oceanography (NIO) in Goa have also found major damage to coral reefs of the Kavaratti and Kadamat islands in Lakshwadweep, which have been ravaged by bacterial diseases besides warmer sea temperatures.

The reasons for the damage in Lakshwadweep, according to NIO are bacterial diseases, while siltation is said to be the main cause of coral bleaching in the Gulf of Kutch. A recent Reef Check survey showed heavy coral deaths in Kadamat with only 3 per cent live coral cover at a depth of 3 metres (m). At 10 m, live coral cover was 7 per cent, while bleaching between 10 per cent to 30 per cent was seen in the Gulf of Kutch in early to mid-May.

"However, in India, a major drawback is that there is no quantitative baseline data on corals," says C L Rodrigues of the department of marine science and technology, Goa University. "Based on earlier qualitative reports, the reefs of the Gulf of Kutch and the Gulf of Mannar have suffered extensive degradation."

According to Rodrigues, the Global Coral Reef Monitoring Network (GCRMN)-India was established in 1997. Recently, the Indian Coral Reef Monitoring Network, set up by the Union ministry of environment and forests, and the GCRMN have joined hands to study the plight of the corals in the Indian subcontinent.

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In warm waters
Global warming is responsible for coral bleaching, say experts. And if climate change goes unchecked death of corals could mean the death knell for many marine species

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TRAMPLED TO DEATH: reef-walking, a popular tourist activity, damages the fragile corals and other marine organisms

Last year's temperatures in the Indian Ocean were more than
2 oc higher than normal, enough to cause bleaching of corals. Every known mass bleaching occurred when temperatures were just 1 oc higher than normal during the warmest summer month

p30_.jpg (25660 bytes)According to a study conducted by the National Oceanic Atmospheric Administration, us, 1998 was the warmest year in 1,200 years. The rate of warming has also been on the rise since the 1970s, says a National Aeronautics and Space Administration study. This gives many scientists reason to believe that corals are but a victim of global warming. "The severity and extent of coral bleaching events cannot be accounted for by localised stresses alone. At this time, it appears that only global warming could have induced such extensive bleaching simultaneously throughout the disparate reef regions of the world," says Rafe Pomerance, deputy assistant secretary of state for environment and development, in a report presented to the us Coral Reef Task Force in March 1999.

The study conducted by Pomerance and his team members, which is also said to be the most complete documentation of the problem ever, concluded that record ocean temperatures caused the largest die-off of corals in recorded history and catalogued coral decline in 60 countries. Last year’s temperatures in the Indian Ocean, for instance, were about 2° C higher than normal, enough to cause the bleaching of corals. According to the Global Coral Reef Alliance (GCRA), every known mass bleaching occurred when temperatures were just 1°C  higher than normal during the warmest summer months.

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Thomas Goreau, president of GCRA, also believes global warming is killing corals and says the worst is yet to come because sea temperatures are expected to soar to record highs again next year. Richard Barber, director of the University of North Carolina Oceanographic Consortium, us, echoes Goreau’s views. "Global warming and increased ultraviolet radiation (resulting from ozone depletion) have the global-scale influence that is characteristic of the scale of the coral responses observed," he says. However, some experts such as Wilkinson see a strong correlation between the widespread coral bleaching in 1997-98 and the El Niño weather phenomenon, resulting in the periodic warming of the Pacific waters. By some measures, the 1997-98 El Niño was the strongest on record. In many parts of the Pacific, El Niño appears to be a significant factor contributing to severe coral bleaching events.

However, the correlation between El Niño and coral bleaching is not apparent for all locations, says Pomerance. "At this time it appears that El Niño by itself cannot account for the extreme warmth of 1998, but is part of a larger climate pattern that influenced temperatures," he says. "However, it should be noted that the 1983, 1987 and 1998 mass coral bleaching events corresponded with record El Niños, and the high sea surface temperatures diminished as the El Niños dissipated," says Wilkinson.

This brings us to the question whether coral bleaching is just a severe, one-off event, as it now appears, or whether events like this will occur more frequently as the world’s atmosphere and waters warm up. Although the conditions in 1998 were worsened by El Niño, recent trends suggest that the threat to the reefs will only increase with time, the report warns. Reefs will not become extinct in the long term, but a single bleaching event will take reefs between 30 to 100 years to recover and "if we go into unrestrained warming, when corals become quite rare, we’d be looking at a recovery time of up to 500 years", says Ove Hoegh-Guldberg, director, Coral Reef Research Institute, Australia. What is worse is that  Hoegh-Guldberg, who has studied corals for the last 15 years, predicts such occurrences to be commonplace by 2020.

Fisherfolk in the Philippines pour drums of poison into the reefs to make fishing easier

In Japan, boys and young men practice what is called the muro-ami fishing technique. Using rocks tied to "scarelines" that are flagged with brightly-coloured streamers, they swim together over the reef and pound on its ridges. This scares the fish living inside the reef crevices, and as they come out the streamers lead them into a semi-circular net known as a muro-ami.

In the Philippines, some fishing communities pour drums of sodium cyanide to temporarily asphyxiate the reef fish. As they float to the sea surface, they are easily netted by their captors.

Probably the worst method used in the Indo-Pacific region is to toss dynamite into schools of reef fish. The force of the explosion ruptures the air bladders that control buoyancy in fishes. The fisherfolk easily harvest the injured fish that float to the surface. Dead or mangled ones and commercially undesirable species are left behind. "Stretches of fishless reefs around the Tanzanian island of Zanzibar, for example, are riddled with holes from the blasting, some as big as 10 metres in diameter," says Barbie Bischof in The Yearbook of Science and the Future 1999.

These are just some of the destructive fishing techniques practised the world over. Though reefs occupy only about 0.2 per cent of the world’s oceans, they provide an estimated 10 per cent of all the fish harvested worldwide, says Bischof.

The dependence on reefs as a means of human sustenance has put added pressure on them. And what has worried coral watchers is the growing trend among people, especially in the Asian countries, to cater to the seafood market, even if it means using destructive fishing practices. "Fishing operations are today spreading to remote areas. Because of the disappearance of large fish in the populated Asian continent, fishing companies are willing to travel even to the South Pacific islands... Because of the high cost of transportation, commercial fleets are harvesting in one sweep, rather than engaging in a sustainable practice that entails smaller hauls and repeated visits," says Bischof. This has resulted in the disappearance of large fish species in some areas. The jewfish, which is of great commercial value in the Caribbean, has virtually disappeared, from the region’s reefs.

However, some experts like C L Rodrigues of the Department of Marine Science and Biotechnology, Goa University believe that "the link with global warming and El Niño has not been conclusively established yet. Hence, it is too early to
suggest any link," especially because bleaching also took place in regions unaffected by El Niño. Other scientists say that the warming of the ocean waters could be the result of nature’s unpredictable flux. "We all hope this is a severe one-time event," said Gregor Hodgson, founder of Ref Watch and a coral ecologist at the Hong Kong University of Science and Technology. "If global warming is involved and bleaching is repeated, then we are in serious trouble," says Hodgson.

Last year’s temperatures in the Indian Ocean were more than 2°c higher than normal, enough to cause bleaching of corals. Every known mass bleaching occurred when temperatures were just 1°c higher than normal during the warmest summer month

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Special thanks to Clive Wilkinson of the Global Coral Reef Monitoring Network, Townsville, Australia, for his contribution to the article

For the rest of the article
"Neptune's Sorrows",  please refer to the printed copy of Down To Earth August 15, 1999 or SUBSCRIBE HERE.


Copyright © CSE  Centre for Science and Environment