What are coral reefs?
Contrary to what many people believe, coral is not a plant but a living organism
(polyp) that is part of a unique ecosystem in which it is estimated that a quarter of all
marine species can be found. Coral reefs are one of the most productive and diverse
communities in the world, which has led to both their appreciation and exploitation.
They are known as the ‘rainforests of the oceans’.
Coral is made of calcium carbonate (limestone), and builds itself up around the
skeleton of dead coral (which is left when a coral polyp dies) in order to increase the
size of a reef. Reefs are therefore constructed from millions of tiny coral polyps
which live together in colonies. These polyps absorb calcium from sea water to build
their limestone skeletons, and when they die these skeletons become what we
recognise as a coral reef. There are two types of coral; reef building or hard coral
(hermatypic) and non reef-building or soft coral (ahermatypic). Reefs also consist of
organisms such as sponges, worms, parrotfish, sea urchins and algae.
What are coral polyps?
Coral polyps are invertebrates that secrete calcium carbonate to form limestone
skeletons, and are the living part of coral. They look like upside down jellyfish,
and form a living layer on the surface of skeletons left behind by dead polyps.
They belong to the same group as jellyfish and sea anemones, and are around
2-3 cm long. Polyps absorb the calcium in sea water to create the limestone
skeletons that form coral reefs when the polyp dies. Coral polyps work in
conjunction with a plant, zooxanthellae, in a process called symbiosis which
produces energy for the coral to live and reproduce. Zooxanthellae are
unicellular algae, and the symbiotic relationship they have with polyps is called
so because it is mutually beneficial. The zooxanthellae photosynthesise and
share the food and oxygen produced with the coral polyp in return for receiving
protection, access to light and carbon dioxide.
Source:
Coral Cay Conservation
http://www.coralcay.org/science/reefs/coral_reef_ecology.php
Coral Reef Alliance
http://www.coralreefalliance.org/aboutcoralreefs/overview.html
US Environmental Protection Agency
http://www.epa.gov/cgi-bin/epaprintonly.cgi
Coral formations vary widely, from
branching trees, large domes and small
layers to organ pipe formations. They also
vary in colour and shape, depending on
variety and environment. Flatter corals tend
to form where there are strong waves,
whereas branch patterns are more common
in sheltered areas. Coral polyps have clear
bodies and their skeletons are white. They
get their beautiful colour from the algae
(zooxanthellae) that live inside their tissue.
Credit: J Nortcliffe
Fringing reef
A fringing reef runs directly along the line of a coast, and extends out from the land
into tropical seas. They are commonly found in the South Pacific, Hawaiian Islands
and the Caribbean.
Barrier reef
A barrier reef is separated from a mainland or island by a wide lagoon, and occurs
further offshore than a fringing reef. This type of reef forms when land masses sink,
allowing fringing reefs to become separated from shorelines by wide channels.
Barrier reefs are found in the Caribbean and Indo-Pacific regions. The Great Barrier
Reef off the coast of Australia is the largest barrier reef in the World, and stretches
for 1,240 miles.
Atoll reef
An atoll reef has a circular formation of continuous reef, which surrounds a lagoon
without a central island. They usually form when islands surrounded by fringing reefs
sink into the sea, or when sea levels rise around them. These islands are often the
tops of underwater volcanoes. Atolls occur in the Indo-Pacific, and the largest one in
the world surrounds a lagoon that is over 60 miles long.
Apron reef
An apron reef is similar to a fringing reef
but has a gentle slope out and downwards
from a point.
Patch reef
A patch reef is often isolated and circular
in shape, usually within a lagoon or bay.
They are common in the area between
fringing reefs and barrier reefs, and rarely
reach the surface of the water.
Ribbon reef
A ribbon reef is a long and narrow reef,
usually associated with an atoll lagoon.
Credit: J Nortcliffe
Table reef
A table reef is similar in shape to an atoll reef, but without the central lagoon.
Coral Reef Facts
- Taking into consideration the economic value of fisheries, tourism and
coastline protection, the cost of destroying 1 km of coral reef is between
US$137,000 and US$1,200,000 over a 25 year period.
- When managed properly, coral reefs can provide about 15 tonnes of fish and
seafood per sq km a year.
- More than 80% of the world’s shallow reefs are over-fished.
- Coral reefs occupy less than a quarter of 1% of the ocean, but are home to
more than 25% of all known fish species.
- According to the World Atlas of Coral Reefs published by the UN
Environmental Programme World Conservation Monitoring Centre, around 58%
of the world’s coral reefs are potentially threatened by human activity.
- Of the 109 countries that coral reefs are found in, 93 have experienced some
kind of coral degradation.
- Between 1876 and 1979, 3 coral bleaching incidents were recorded, whereas
between 1980 and 1993 60 incidents were recorded. In 2002 more than 400
examples were recorded.
- We have already lost 27% of the world’s coral reefs. If this continues at the
present rate, 60% of the world’s coral reefs will be lost in the next 30 years.
- The economic value of Indonesia’s reefs is estimated at US$1.6 billion
annually.
- Southeast Asia has 34% of the world’s coral reefs, spread over 100,000 sq km
and providing a home to over 600 reef building species.
- Indonesia and the Philippines hold nearly 80% of the world’s threatened reefs.
- Approximately 8 million coral reef species are estimated to be undiscovered.
- Of the 7500 known species of coral approximately 5000 are now extinct.
- Approximately 40% of the reefs that were seriously damaged by bleaching in
1998 are either recovering or have recovered.
Sources:
WWF
http://www.panda.org/about_wwf/what_we_do/marine/what_we_do/coral_reefs/
about/Coral_facts.cfm
American Association for the Advancement of Science:
Moore, Franklin and Best, Barbara ‘Coral reef crisis: Causes and
Consequences’, found at
http://www.aaas.org/international/africa/coralreefs/ch1.shtml
Coral Cay Conservation:
http://www.coralcay.org/science/reefs/how_are_reefs_threatened.php
http://www.coralcay.org/science/reefs/coral_reef_ecology.php
Where are they located and why?
Coral reefs are found in all the oceans of the world but are most common between
the Tropics of Cancer and Capricorn, mainly because reef-building coral is prevalent
in these areas. The main areas in the Western Atlantic Ocean to find reefs are
Bermuda, the Bahamas, the Caribbean, Belize, Florida and the Gulf of Mexico. The
Indo-Pacific region also has large amounts of reefs, which are located in an area
which extends from the Red Sea and the Persian Gulf, through the Indian and Pacific
Oceans to the western coast of Panama.
Reef-building corals are mainly found in shallow water (generally under 50 metres
deep but some can survive to 90 metres), where sunlight can reach the ocean floor
to provide the corals with the energy they need to grow. This means that growth
increases depending on how clear the water is, as less light is absorbed by clearer
water. Corals do not photosynthesise, but live with microscopic algae which
photosynthesise for them which is why they need sunlight to live. Non reef-building
coral has been found in deeper water (up to 6,000 metres deep), where it survives by
feeding on the organic matter in the ocean currents rather than through the energy
from sunlight. Reefs do not form around the mouths of rivers due to larger than
normal amounts of sediment and pollution.
Credit: J Nortcliffe
Coral reefs need warm water temperatures
of between 20-28 ºC (68-82 ºF) in
order to grow, and find this warm
water along the eastern shores of
major
land
masses.
Reef
development is more common in
areas that experience strong wave
action. This is because waves carry
food, nutrients and oxygen to the
reef, distribute coral larvae and
prevent sediment from smothering
the reef. The formation of a coral
polyp’s
skeleton
requires
the
precipitation of calcium in the
surrounding water. This precipitation occurs when water temperatures and salinity
are high, and carbon dioxide levels are low. These conditions are provided by the
warm, shallow tropical waters between 30 degrees N and 30 degrees S latitudes.
Why are coral reefs important?
The value of a coral reef is generally assessed depending on its economic and
ecological value. However, there are other values which are becoming increasingly
important as we strive to conserve this fragile ecosystem. Coral reefs are an
excellent indicator of environmental change and the ecological quality of an area.
Ecosystem / Diversity
Coral reefs provide a natural habitat for a wide variety of fish species and other
plants and creatures. Reef
systems are estimated to be
home to around 1 million different
species, all of which have
adapted to their surroundings to
tolerate specific diets, their
unique habitat and the threat of
reef predators. Grazing fish, sea
urchins, sponges and other
organisms can be found within
the reef ecosystem, all of which
help to break down dead coral
polyps and build the reef. Coral
reefs have around six trophic
levels. Coral also influences the
Credit: J Nortcliffe
amount of carbon dioxide in the oceans, as coral polyps fix carbon dioxide to form
limestone. This acts as a ‘carbon sink’ for excess carbon dioxide in the atmosphere
and oceans.
Tourism
If managed in a sustainable way, tourism can not only provide income for the
countries that open their reefs to holiday makers, it can also ensure reefs are
protected for generations to come via management schemes, education and
awareness. Billions of pounds are spent each year on diving tours, fishing trips,
hotels, restaurants and tourist-based business centred around reef areas, all of which
create income for a massive number of people. Reefs also contribute to the formation
of the sandy beaches we find in these areas via the disintegration of coral over time.
Economy
According to one estimate, coral reefs provide goods and services worth
approximately $375 billion each year, which is amazing when you consider that reefs
cover less than 1% of the earth’s surface. The economic benefits of a reef include
coastline protection services (protecting coasts from waves and storms etc), places
for tourism and recreation, sources of food, medicines and livelihoods. Studies have
shown that on average, countries with coral reef industries derive more than half their
gross national product from them.
Medicine
Coral reef has been found to contain a variety of compounds which are useful in
medicine. Recent research has linked these compounds to treatments for heart
disease, cancer, HIV, arthritis, bacterial infections and viruses. For example, a
Caribbean reef sponge provides chemicals which are used in a well known HIV
treatment. Coral’s skeletal structure has also been used to make bone grafting
material.
Coastline protection
Coral reefs act as filters for the water around a
shoreline, helping to maintain good water quality
in the area around the reef. Reefs that are
located offshore form barriers, and provide
shelter from ocean waves by acting as
breakwater. They are also self-building and selfrepairing, thus providing an excellent source of
coastal protection in areas that would perhaps not
otherwise be able to implement such a scheme.
Reefs also protect coastlines from storms and
floods, preventing loss of life, property and
erosion. They also help to produce the sandy
beaches that are popular with tourists, as the
debris caused by the breakdown of the reef
skeletons is washed ashore.
Credit: J Nortcliffe
References and Sources
American Association for the Advancement of Science
Birkeland, Charles ‘Can ecosystem management of coral reefs be achieved?’, found
at: American Association for the Advancement of Science
http://www.aaas.org/international/africa/coralreefs/ch3.shtml
Moore, Franklin and Best, Barbara ‘Coral reef crisis: Causes and Consequences’,
found a: American Association for the Advancement of Science
http://www.aaas.org/international/africa/coralreefs/ch1.shtml
Spruill, Vikki and Dropkin, Lisa, ‘Ocean Attitudes 2001: Conservation through
consumer action’, found at: American Association for the Advancement of Science
http://www.aaas.org/international/africa/coralreefs/ch5.shtml
Bowen, Ann and Pallister, John (2001) ‘A2 Geography’, Heinemann
Coral Cay Conservation:
http://www.coralcay.org/science/reefs/how_are_reefs_threatened.php
http://www.coralcay.org/science/reefs/why_conserve_reefs.php
http://www.coralcay.org/science/reefs/coral_reef_ecology.php
Coral Reef Alliance
http://www.coralreefalliance.org/aboutcoralreefs/overview.html
http://www.coralreefalliance.org/aboutcoralreefs/care.html
http://www.coralreefalliance.org/aboutcoralreefs/threats.html
Digby, Bob (Ed) (2000) ‘Changing Environments’, Heinemann
Elcome, David (1999) ‘The Fragile Environment: Pollution and Abuse’, Nelson
Thornes
Sea World Adventure Parks
http://www.seaworld.org/infobooks/coral/deathcr.html
http://www.seaworld.org/infobooks/coral/coralcr.htlm
http://www.seaworld.org/infobooks/coral/habdiscr.html
The International Ecotourism Society
http://www.ecotourism.org/index2.php?what-is-ecotourism
University of the Virgin Islands
http://manta.uvi.edu/coral.reefer/threats.htm
US Environmental Protection Agency
http://www.epa.gov/cgi-bin/epaprintonly.cgi
Warn, S and Naish, M (Eds), 2000 ‘Changing Environments: AS level geography for
Edexcel B’, Longman
Wikipedia
http://www.wikipedia.org/wiki/coral_reefs
Wilkinson, Clive (Ed) (2004) ‘Status of Coral reefs of the World 2004, Volume 1’,
with the Coral reef Monitoring network, Australian Institute of Marine Science
WWF
http://www.panda.org/about_wwf/what_we_do/marine/what_we_do/coral_reefs/about
/Coral_facts.cfm