down to earth
environment and you
Corals are to the oceans what tropical
rainforests are to land. Known as Neptunes 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?
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
Corals, the rainforests of the oceans, are dying. Victims of global warming, scientists
say 10 per cent of the Earths 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 Caribbeans and the
Atlantic Ocean," says Wilkinson. Only the Central Pacific region seems to have been
Coral reefs have suffered the most damage in
heavily-populated coastal areas, largely in developing countries
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
Wilkinson points out four overlapping levels of
severe: with around 50-70 per cent mortality and with some coral recovery in
Kenya, Seychelles, Japan, Thailand, Vietnam, and Belize;
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,
insignificant or no bleaching: in large areas of the worlds 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
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;
southern and eastern Caribbean.
|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 alls 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
"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.
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
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
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 years 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.
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
Goreaus 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 worlds 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, wed 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
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 worlds 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
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 natures 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 years 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
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
refer to the printed copy of Down
To Earth August 15, 1999
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