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Great Barrier Reef
The Great Barrier
Reef is undisputed as one of the world’s most important natural assets.
The Great Barrier Reef is the
world's largest coral reef system, composed of roughly 3,000 individual reefs
and 900 islands stretching for 2,600 kilometres (1,616 mi) over an area of
approximately 344,400 square kilometres (132,974 sq mi).
Geographical LocationThe
reef is located in the Coral Sea, off the coast of Queensland in northeast
Australiafrom just south of the Tropic of Capricorn to the coastal waters of
Papua New Guinea 24°30'N-10°41'S, 145°00'-154°00'E.
Climate
The Great Barrier Reef has a tropical climate influenced primarily by two
features of the southern hemisphere circulation: the equatorial low pressure
zone during the summer months and the sub-tropical high pressure zone during the
winter months. As the area lies between the continental land mass of Australia
and the open ocean of the South Pacific, its climate is also strongly influenced
by both the adjacent land mass and oceanic effects. Wind patterns are dominated
for the greater part of the year by the south-east trades. During January to
March, north-westerlies prevail in the north of the area under the influence of
the inter-tropical monsoonal front. The rainfall is seasonally and
geographically variable. The wettest period is summer, under the influence of
the monsoon and irregular tropical cyclones and depressions. Heavy rain may
occur in the south during winter. Air temperatures vary betweenan average
maximum of approximately 30°C in January and 23°C in July and an average
minimum of approximately 24°C in January and 18°C in July. Mean water surface
temperature is at a maximum during February and at a minimum during July
Wildlife There
are over 1,500 species of fish, 400 species of coral, 4,000 species of mollusc
and 242 species of bird within the park, plus a great diversity of sponges,
anemones, marine worms and crustaceans. The site includes major feeding grounds
for dugongDugong dugon. Several cetaceans are present, including humpback whale Megaptera
novaengliae , minke whale Balaenoptera acutorostrata and killer whale
Orcinus orca. Dolphins include bottle nose Tursiops truncatus,
Irrawaddy Orcaella brevirotris and Indo-Pacific humpback Sousa
chinensis. Offshore, spinner dolphin Stennella longirostris is also
occasionally seen. There are nesting grounds of world significance for green
turtle Chelonia mydas and loggerhead Caretta caretta , and
habitat for four other species of marine turtle.
Australia
has the largest area of coral reefs (purple) of any nation. (Inset) Acropora
corals in Ningaloo Reef
Credit:
Australia Department of the Environment, Water, Heritage and the Arts
Bigger than the entire area of
Italy, it is probably the best known marine protected area in the world. The
Great Barrier Reef's great diversity reflects the maturity of the ecosystem,
which has evolved over hundreds of thousands of years. It is the world's most
extensive coral reef system and is one of the world's richest areas in terms of
faunal diversity.
Satellite
image of part of the Great Barrier Reef adjacent to the Queensland coastal areas
of Proserpine and Mackay
Credit:
NASA
The Great Barrier Reef can be
seen from outer space and is the world's biggest single structure made by living
organisms.
River Plumes
Threaten Great Barrier Reef
NASA
image courtesy the MODIS Rapid Response Team, Goddard Space Flight Center
NASA Earth
Observatory-In late February 2007, NASA satellite images revealed that even
the outer portions of the Australia’s Great Barrier Reef can be bathed in
land-based pollution carried far offshore by plumes of river water. Conventional
thinking was that river plumes affected only the lagoon and the inner portions
of the reef. But images from the Moderate Resolution Imaging Spectroradiometer (MODIS)
on NASA’s Terra satellite verify a new
theory that not even the outer reefs are spared the impact of land-based
pollution, which includes excess sediment, fertilizers, and pesticides.
This image from February 9, 2007,
shows plumes of sediment flowing into Princess Charlotte Bay, which is about
halfway down the east coast of Queensland’s Cape York Peninsula. After heavy
rains fell in late January and early February, several rivers were emptying
muddy water into the bay. The plumes merge into a 12-kilometer-wide river of
sediment-laden water (flanked by white arrows) that heads almost due north and
washes over a large coral reef. The sediment makes the normally
turquoise-colored reef look greenish-brown. The plume veers northeastward away
from the first reef, and although the plume becomes fainter, it does reach the
outer reef. Similar plumes are visible along much of the coastline (visible in
the large version of the image).
According to the scientists at
Australia’s Commonwealth Scientific and Industrial Research Organisation who
first publicized them, the images provide proof that scientists monitoring and
trying to safeguard the health of Australia’s Great Barrier Reef must begin to
consider the effect of extreme coastal flooding events that can spread pollution
much farther than they previously thought.
The Great Barrier Reef could soon
be another casualty of climate change
Carbon dioxide is increasing the
acidity of the oceans. Ocean acidity is increasing at a much faster pace
according to marine scientists meeting in Australia's capital, Canberra, at the
Coral Reef Futures 07 Forum, October 18-19, 2007. "It appears this
acidification is now taking place over decades, rather than centuries as
originally predicted. It is happening even faster in the cooler waters of the
Southern Ocean than in the tropics. It is starting to look like a very serious
issue." said Professor Malcolm McCulloch of the Centre of Excellence for
Coral Reef Studies (CoECRS) and the Australian National University.
Over time, the acidic water
dissolves the shells of coral and marine life. The Barrier Reef is losing one to
two percent of coral each year and all of the reef’s coral could be gone in 40
years. The environmental problem is not just restricted to Australia, almost
half of the world’s reefs are under threat, with 44 percent of the world’s
reefs already severely degraded.
Bleaching
on the Great Barrier Reef
Images
by Norman Kuring and Robert Simmon, based on data provided by Scarla Weeks,
University of Queensland
NASA Earth Observatory-Summer
officially came to an end in Australia on March 20, 2006. For northeastern
Australia (Queensland and New South Wales), it was the hottest summer on record,
according to the Australian Bureau of Meteorology, and that was bad news for
Australia’s Great Barrier Reef. Up to 50 percent of coral bleached at certain
inshore locations in the southern Great Barrier Reef. In general, hot water puts
coral under stress. Under such conditions, the coral expels the tiny algae,
zooxanthellae, that live in symbiosis with it. The algae give the coral its
color and produce nutrients through photosynthesis, so when the algae are
expelled, the coral turns white and eventually dies. The process is called coral
bleaching.
But coral bleaching is only one
symptom of an ecosystem in hot water: high temperatures have a negative impact
on other parts of the marine ecosystem as well. “All marine species operate
within a range of environmental parameters. Once this changes, the effects
cascade through the food-chain,” says Scarla Weeks, an ocean researcher at the
University of Queensland, Australia, funded by the Pew Institute for Ocean
Science. Ocean currents are driven in part by water temperature, and if a
current shifts, this may impact an entire ecosystem. Warmer temperatures may
result in decreased concentrations of phytoplankton, the tiny plants that grow
in the upper sun-lit layer of the ocean. Because phytoplankton form the base of
the marine food chain, their decline will cascade through the food chain. Larger
animals like fish will have little to eat and either die or move elsewhere. Loss
of fish impacts the sea birds that feed on them. In 2002, says Weeks, high sea
surface temperatures led to the worst bleaching event on record in the Great
Barrier Reef. The same year, 50 percent of seabird chicks on Heron Island in the
southern Great Barrier Reef starved because the adult birds were unable to find
enough fish.
The chain from warm water to
coral bleaching and sea bird deaths is long and complex, but satellite data may
provide some insight into the mechanisms controlling the chain. Weeks is using
NASA sea surface temperature and chlorophyll concentration data to study these
complex ocean processes. The images above illustrate sea surface temperatures
and chlorophyll concentrations as observed by the Moderate Resolution Imaging
Spectroradiometer (MODIS) on NASA’s Aqua
satellite between February 6 and February 20, 2006. Warm pink and yellow tones
show where sea surface temperatures were warm in the top image. The warmest
waters are the shallow waters over the reef near the coast, where coral
bleaching was most severe this summer.
The lower image shows chlorophyll
concentrations, where high concentrations (yellow) generally point to a high
concentration of phytoplankton in surface waters of the ocean. In this image,
the bright yellow dots actually represent the coral reefs, and not surface
phytoplankton. Ocean waters are clear off Australia’s northeast coast. The
patterns shown here reveal the movement of ocean currents, with lower
chlorophyll concentrations representing oceanic waters. By studying the changing
patterns, scientists can monitor the dynamics of the Great Barrier Reef and
every link in that marine ecosystem.
Credit: NASA, Government of Australia
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