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Coral
Reef
It is a type of biotic reef developing in tropical
waters. Although corals are major contributors to
the overall framework and bulk material comprising
a coral reef, the organisms most responsible for
reef growth against the constant assault by ocean
waves are calcareous algae, especially, although
not entirely, species of red algae.
Water temperature of 20–28 °C (68–82
°F) is an optimal range for proper growth and
health of coral reefs. Coral reefs are found in
all oceans of the world, except the Arctic Ocean,
generally between the Tropic of Cancer and the Tropic
of Capricorn, because reef-building corals live
in these waters. Reef-building corals are found
mainly in the photic zone (<50m), where the sunlight
reaches the ground and offers the corals enough
energy. The corals themselves do not photosynthesise,
but they live in a symbiotic relationship with types
of microscopic algae that photosynthesise for them.
Because of this, coral reefs also grow much faster
in clear water, which absorbs less light.
Such reefs take a variety of forms, defined as the
following:
* Apron reef — short reef resembling a fringing
reef, but more sloped; extending out and downward
from a point or peninsular shore.
* Fringing reef — reef extending directly out
from a shoreline, and more or less following the
trend of the shore.
* Barrier reef — reef separated from a mainland
or island shore by a lagoon; see Great Barrier Reef.
* Patch reef — an isolated, often circular
reef, usually within a lagoon or embayment.
* Ribbon reef — long, narrow, somewhat winding
reef, usually associated with an atoll lagoon.
* Table reef — isolated reef, approaching an
atoll type, but without a lagoon.
* Atoll reef — a more or less circular or continuous
barrier reef surrounding a lagoon without a central
island; see atoll.
Importance of Coral Reefs
Coral reefs provide a natural habitat and massive
protection for different species of fish. They are
not plants; they are living organisms that provide
an environment for fishes to breed. Without them,
fish in the ocean are homeless. According to professor
Christie’s lecture, corals are colonial organisms
that need to be exposed to sun, in order for them
to grow. The corals also influence the amount of
carbon dioxide in the ocean, because coral polyps,
which are tiny invertebrates (cnidarians) that look
like upside-down jellyfish, fix carbon dioxide to
form limestone. This is a major process that acts
as a 'carbon sink' for excess carbon dioxide in
the atmosphere, as well as maintaining an environment
of exceptionally high biodiversity despite relatively
poor nutrient availability.
Biology
See also: Coral
The building block of coral reefs are the skeletons
of generations of hard corals, composed of calcium
carbonate. As each polyp dies, it leaves behind
its skeletal structure, upon which the next generation
of polyps grow, enlarging the reef. Grazing fish
(such as parrotfish), sea urchins, sponges and other
organisms break down the coral skeletons into fine
fragments, which settle into spaces in the reef
structure.
Coral reefs are among the most diverse and productive
biological communities on Earth. The reef structure
provides habitat and shelter to a wide variety of
marine plants and animals - it is estimated that
a quarter of marine life lives in or around coral
reefs. Additionally, corals act as water filters,
increasing water quality in the vicinity of the
reef. Offshore, the reef structure acts as a breakwater,
protecting coastlines from ocean waves. The wide
variety of flora and fauna has turned some coral
reefs and the islands and coastal areas near them
into popular tourist attractions.
Deep water reefs
In December 2004, United States Geological Survey
(USGS) researchers announced the confirmation of
the discovery of the deepest coral reef ever found
in the United States. The reef is in the Pulley
Ridge area, a north-south-trending drowned barrier
island, more than 60 miles (100 km) long, approximately
40 miles (70 km) west of Dry Tortugas National Park.
It is up to three miles wide and about 20 miles
long (5 km wide and 30 km long), and located at
a depth that ranges from 200 to 250 feet (60 to
80 m). Unlike most coral reefs, which tend to grow
vertically, Pulley Ridge coral grows flat, an adaptation
to the limited penetration of light at that depth
to increase surface area exposed to sunlight.
Similar deep reefs occur in other parts of the world,
e.g. the Mingulay reef complex and the Darwin Mounds
located off the west of Scotland in about 150 metres
of water.
Threats to Reefs
Coral Reef bioerosion |
Bioerosion (coral damage) such as this may be caused
by coral bleaching.
Humans continue to represent the single biggest
threat to coral reefs. In particular, land-based
pollution and over-fishing are the most serious
threats to these ecosystems. The live food fish
trade has been implicated as one driver of decline
due to the use of cyanide in the capture of fish.
Rising water temperatures produce toxins in the
coral tissue, due to bleaching.
High levels of land development have also been threatening
the survival of coral reefs. Within the last 20
years, the once thick mangrove forests, which absorb
massive amounts of nutrients from runoff caused
by farming and the construction of roads, buildings,
ports, channels, and harbors, are being destroyed.
Nutrient-rich water causes algae to thrive in coastal
areas in suffocating amounts, also known as algal
blooms.
Due to the increased demand for live reef fish in
North America and Europe, the use of cyanide fishing
has increased in the Indo- Pacific region. 85% of
the of the world’s aquarium fish are caught
in this region and almost all of them are caught
using cyanide. Cyanide is used to stun the fish,
in order to easily capture them for trade. It is
detrimental to the organs of fish, which would explain
the 90% mortality rate of cyanide captured fish.
Cyanide is also very destructive to the surrounding
coral reef ecosystems. It kills corals and other
reef invertebrates. Corals are also harmed by the
poor harvesting practices of the live fish trade.
Fishermen sometimes pound on the reef with crowbars
and rocks to scare fish into nets or pry corals
apart to retrieve stunned fish.
A major catalyst of cyanide fishing is poverty within
fishing communities. In areas like the Philippines
where cyanide is regularly used to catch live aquarium
fish, the percentage of the population below the
poverty line is 40%[2]. In such developing countries,
a fisherman might resort to such unethical practices
in order to prevent his or her family from starving.
Dynamite fishing is another extremely destructive
method that fishermen use to harvest small fish.
The procedure of dynamite fishing starts with a
bottle that is filled with explosives made of potassium
nitrate, once the dynamite goes off the explosion
brings about an underwater shockwave causing the
swim bladders of fish to burst making them float
to the top. A second blast is often set off after
the first to kill any larger predators that are
attracted to the initial kill of the smaller fish.
This method of fishing does not only kill small
fish but also claims the lives of many reef animals
that are not edible or wanted, such as the coral
itself. Areas that used to be full of coral now
are like desert sand, no sign of coral or any other
reef animals that used to inhabit it.
During the 1998 and 2004 El Niño weather
phenomenons, in which sea surface temperatures rose
well above normal, many tropical coral reefs were
bleached or killed. Some recovery has been noted
in more remote locations, but global warming could
negate some of this recovery in the future. Toxins
in the tissue are produced when the water temperatures
climb, causing coral bleaching. However, Ben McNeil
of the University of New South Wales hypothesises
that reefs are not in decline, and may exceed pre-industrial
levels by as much as 35 percent by 2100, especially
because of the positive influence of global warming.
However, growth in some reefs due to global warming
is expected to be offset by declines in other reefs,
due to the comfortable temperature range for a coral
being close to the temperature at which they bleach.
In general, Southeast Asia coral reefs are at risk
from damaging fishing practices (such as cyanide
and blast fishing), overfishing, sedimentation,
and bleaching. A variety of activities, including
education, regulation, and the establishment of
marine protected areas, are underway to protect
these reefs.Indonesia has nearly 33,000 square miles
of coral reefs. Its waters are home to a third of
the world’s total corals and a quarter of its
fish species. Coral reefs of Indonesia are located
in the heart of the Coral Triangle and have been
victim to destructive fishing, unregulated tourism,
and bleaching due to climatic changes. Many of the
diverse coral reefs are being smothered by sediment
and poisoned from cyanide fishing and organic pollution.
Data from 414 reef monitoring stations throughout
Indonesia in 2000 found that only 6 percent of Indonesia’s
coral reefs are in excellent condition, 24 percent
are in good condition, and approximately 70 percent
are in poor to fair condition (2003 The Johns Hopkins
University). According to The Nature Conservancy
organization, if the destruction increases at the
current rate, 70% of the world’s coral reefs
will have disappeared within our life times
See Also
* Coral
* Reef
* Atoll
* Southeast Asia coral reefs
* Marine conservation
* Diving locations
* Great Barrier Reef
See also:
• Australia
• Belize
• Nassau
Grouper
• This article is licensed under the GNU
Free Documentation License.
• It uses material from the Wikipedia
article "Coral Reef".
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