Coral reefs decimated by 2050, Great Barrier Reef's coral 95% dead

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Coral reefs decimated by 2050, Great Barrier Reef's

coral 95% dead

Rhett A. Butler, mongabay.com

November 17, 2005

 

Source >

http://news.mongabay.com/2005/1117-corals.html

 

 

Australia's Great Barrier Reef could lose 95 percent

of its living coral by 2050 should ocean temperatures

increase by the 1.5 degrees Celsius projected by

climate scientists. The startling and controversial

prediction, made last year in a report commissioned by

the World Worldwide Fund for Nature (WWF) and the

Queensland government, is just one of the dire

scenarios forecast for reefs in the near future. The

degradation and possible disappearance of these

ecosystems would have profound socioeconomic

ramifications as well as ecological impacts says Ove

Hoegh-Guldberg, head of the University of Queensland's

Centre for Marine Studies.

 

 

Hoegh-Guldberg, speaking at the Carnegie Institution

Department of Global Ecology at Stanford University,

says the most important threat facing the Great

Barrier Reef and other reefs of the world is higher

sea temperatures that cause thermal stress for corals.

 

Corals are tiny animals that live in colonies and

derive nourishment and energy from a symbiotic

relationship with zooxanthellae algae known as

dinoflagellates. Coral reefs are formed over the

course of thousands of years as limestone skeletons

constructed by corals accumulate and form a structural

base for living corals. Research indicates that is

takes roughly thousand years for a reef to add a meter

of height. Individual corals are capable of faster

growth -- about one meter every hundred years -- but

wave action and other forms of disturbance moderates

overall reef growth.

 

Great Barrier Reef in Australia

The Great Barrier Reef is the world's largest reef,

stretching more than 2,300km along the northeast coast

of Australia. Made up of about 2,900 unconnected coral

reefs and roughly 900 islands, the Great Barrier Reef

is home to over 1,500 species of fish and 400 species

of coral making it one of the most important marine

ecosystems on Earth. Scientists consider it Earth's

largest living organism which makes it the only

individual living thing visible from space.

 

While the Great Barrier Reef is one of the world's

healthiest reefs, coral reefs are particularly fragile

ecosystems, partly due to their sensitivity to water

temperature. When corals are physiologically stressed

-- as is the case when water temperatures are elevated

-- they may lose much of the their symbiotic algae, an

event known as " bleaching. " Corals can recover from

short-term bleaching, but prolonged bleaching can

cause irreversible damage and subsequent death.

 

The first coral bleaching on record occurred in 1979.

Since then, there have been six events, each of which

has been progressively more frequent and severe. In

the El Niño year of 1998, when tropical sea surface

temperatures were the highest yet in recorded history,

coral reefs around the world suffered the most severe

bleaching on record. 48% of reefs in the Western

Indian Ocean suffered bleaching, while 16% of the

world's appeared to have died by the end of 1998. 2002

was even worse: 60 to 95 per cent of individual reefs

of the 110,000 square mile (284,000 square kilometer)

Great Barrier Reef suffered some bleaching, while

reefs in Palau, the Seychelles, and Okinawa suffered

70-95% bleaching. Early surveys suggest the Caribbean

is currently in the midst of a serious event. While

most of these reef ecosystems have recovered to some

degree, warmer water temperatures in the future may

have a more lasting impact.

 

Great Barrier Reef in Australia

" An increase in frequency of coral bleaching may be

one of the first tangible environmental effects of

global warming, " said Dr. Arnold Dekker of Australia's

Commonwealth Scientific and Industrial Research

Organisation (CSIRO) in a European Space Agency news

release. " The concern is that coral reefs might pass a

critical bleaching threshold beyond which they are

unable to regenerate. "

 

Hoegh-Guldberg agrees. " By 2050 bleaching may be an

annual event, that is, if there are still reefs around

to be bleached. If you have bleaching events every

four years and they take 15-20 to recover, you will

start to see bleached reefs not recovering. They will

be dying, " he adds.

 

Acidic Oceans

 

While rising sea temperatures are likely to have the

biggest impact of coral reefs in the future,

Hoegh-Guldberg notes are there factors that will

affect the health of coral reefs including changes in

sea level, elevated storm frequency and intensity,

altered ocean circulation, variation in precipitation

and land runoff, and increasing ocean acidification.

 

Ocean acidification is of particular concern to

scientists because it is crucial to the formation of

coral. Coral and other marine organisms use free

carbonate ions in sea water to build calcium carbonate

shells and exoskeletons, but as atmospheric carbon

dioxide levels rise and more carbon dioxide is

absorbed by the world's oceans, sea waters become

increasingly acidic by stripping out carbonate ions.

Lower carbonate ion concentrations make it more

difficult for organisms to form shells, leaving them

vulnerable to predators and environmental conditions.

In the past, changes in ocean acidity have caused mass

extinction events. According to a study published in

the September issue of Geology, dramatically warmer

and more acidic oceans may have contributed to the

worst mass extinction on record, the Permian

extinction. During the extinction event, which

occurred some 250 million years ago, about 95% of

ocean's life forms became extinct. The same fate could

befall modern day marine life. In September 2005, a

team of scientists writing in Nature warned that by

2100, the amount of carbonate available for marine

organisms could drop by 60%. In surface ocean waters,

where acidification starts before spreading to the

deep sea, there may be too little carbonate for

organisms to form shells as soon as 2050.

 

 

Hoegh-Guldberg believes an atmospheric carbon dioxide

concentration of 500 parts-per-million (ppm) is a key

threshold for coral reefs. " Beyond 500 ppm coral reefs

may no longer exist. Much of the Pacific Ocean will

likely be marginal for coral reefs while net

calcification rates will be approaching zero " says

Hoegh-Guldberg. Currently the concentration of carbon

dioxide in the atmosphere stands around 380 ppm but

the Intergovernmental Panel on Climate Change (IPCC)

projects that if no precautionary action is taken,

carbon dioxide concentrations will rise by 2050 to

between 450 and 550 ppm.

 

Worldwide impact

 

The degradation and loss of coral ecosystems in will

likely have a wide-ranging impact on the world

economy. Hoegh-Guldberg points out that more than 500

million people live within 100 kilometers of coral

reefs, many of whom rely on reefs and the services

they provide for daily subsistence. Should reefs

become severely damaged by climate change it could

well create a class of ecological refugees in need

assistance.

 

Further reefs play an important role in buffering

adjacent shorelines from wave action, erosion, and the

impact of storms. For example Moorea in French

Polynesian, only experiences a 10 cm tidal range due

to its protective barrier reef. Should the reef die

and begin to crumble, the island's low-lying

structures could be at risk.

 

Impact of a dying Great Barrier Reef in Australia

 

Australia may be the best example of the potential

ramifications of dying reefs. Though Australia is

among the world's most developed countries, a damaged

Great Barrier Reef would likely have a significant

impact on the country's economy. A recent study found

the reef is worth more to Australia as an intact

ecosystem than an extractive reserve for fishing.

 

Each year more than 1.8 million tourists visit the

reef, spending an estimated AU$4.3 billion (Australian

dollars) on reef-related industries from diving to

boat rental to posh island resort stays. Revenue from

tourism -- popular activities include snorkeling;

scuba diving; fishing; glass-bottomed boat and

semi-submersible vessel excursions -- dwarfs the

commercial and recreational fishing industries which

generate $360 million (Australian dollars) annually.

Furthermore, tourism is an important source of

employment: in 1998-1999, more than 47,600 people were

employed in the sector compared to around 2,000

involved in commercial fishing in the region.

 

Tourism has given the Australian government an

incentive to preserve the reef and last summer it

banned all forms of extraction in one-third of the

Great Barrier Reef Marine Park, making it the largest

fully protected area of ocean in the world. The

protected area will also benefit the fishing industry

by serving as a nursery for fish-breeding to restock

the entire reef.

 

Great Barrier Reef in Australia

The reef also offers great potential for Australia's

nascent but blossoming biotech industry in the form of

compounds derived from corals and other organisms that

live in the region. Sessile invertebrates -- like

corals -- have a special affinity for providing

medicinally valuable compounds through their

production of toxic chemicals used for defense.

Several promising drugs have been developed from coral

and other invertebrate species.

 

There is little doubt that the Great Barrier Reef, as

a viable and relatively intact ecosystem, will

continue to play an important role in the thriving

Australian economy. The big question is, how long will

it remain viable and intact?

 

Disagreement

 

Some scientists argue that the Great Barrier Reef and

other coral ecosystems may be around longer than has

been suggested by Hoegh-Guldberg's scenario. Critics

say his scenario does not the current level of

uncertainty about either the impact of warmer waters

on the reefs, or likely climate change -- IPCC

projections have been hotly debated.

 

Since the fossil record for corals is spotty -- the

" resolution " for prehistoric dating is only 400 years

-- so the impact of abrupt changes on coral are

difficult to detect. While corals have certainly

persisted through warmer and more acidic periods in

Earth's geologic history, Hoegh-Guldberg suspects

corals will face a difficult adjustment period in the

face of rapidly rising sea temperatures and falling

carbonate ion concentrations.

 

" Biological adaptations can't keep pace with the

forecasted level of change, " says Hoegh-Guldberg. " In

the past the time scale was likely thousands of years,

not decades. "

 

Hoegh-Guldberg argues that coral reefs will likely

recover in geologic terms, but not in terms of a human

lifetime. The short term impact of dying and degraded

reefs will be significant.

 

" For a tour operator, two years of bleached coral can

mean the difference in putting food on the table or

finding a new job. The tourism industry will be hit

especially hard by worsening bleaching events. "

 

Over the longer term, reefs will recover. According to

Hoegh-Guldberg model, under the best-case global

warming scenario -- where temperatures stabilize

around 2100 -- the Great Barrier Reef will recover

within a century. Under the pessimistic, it will take

at least 500 years for the reef to regenerate,

populated by coral species adapted to living in warmer

waters. Hoegh-Guldberg says reefs are unlikely to

migrate to cooler, higher latitude waters due to other

conditions -- including light levels and ion

concentrations -- required for their growth.

 

Despite a bleak future, Hoegh-Guldberg doesn't believe

reef conservation and research efforts should be

abandoned.

 

" There is still a lot we don't know about coral reefs.

We need to understand these ecosystems to be totally

effective in their preservation. Technologies still in

their infancy may make it possible for us to moderate

some of the effects of climate change on coral reefs. "

 

 

 

 

 

 

 

 

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