Essay on Coral Reefs

This essay has a total of 2086 words and 11 pages.

Coral Reefs


Coral, common name for members of a large class of marine invertebrates characterized by a
protective calcium carbonate or horny skeleton. This protective skeleton is also called
coral. Corals are divided into two subclasses, based on differences in their radial
symmetry. One subclass consists of colonial, eight-tentacled animals, each with an
internal skeleton. Among them are whip corals, gorgonians, and the red coral used in
making jewelry. Members of the other subclass commonly have six tentacles, or multiples of
six, but other patterns are also observed. They include the stony, or true, corals.
Another class of the same phylum also contains forms known as coral that are not
considered here. Coral reefs are arguably the world's most beautiful habitats. Coral reefs
have been called the rainforests of the oceans, because of the rich diversity of life they
support. Scientists have not yet finished counting the thousands of different species of
plants and animals that use or live in the coral reef.

Materials and Methods

There are three types of coral reefs: fringing reefs, barrier reefs, and atolls. Fringing
reefs are located close to shore, separated from land by only shallow water. Barrier reefs
lie farther offshore, separated from land by lagoons more than ten meters deep. Atolls, on
the other hand, are formed far offshore and they make a ring-shaped reef that close a
circular lagoon.

Coral reefs are the largest biological structures on the planet, with the largest being
the Great Barrier Reef covering over 2000 kilometers along the east coast of Australia
(Focus, 1995). The reef is said to be 500,000 to 2,500,000 years old and is said to be
visible from the moon.(Scientific, 1987).

There is only one large threat to this beautiful structure and that is the carelessness of
man. Silt from deforested lands and pollution from crowded coastlines choke them, and
overuse by coal miners, fisheries, and even tourists deplete and destroy coral reefs.
There are many more factors, which add to the destruction of the coral reefs, which if not
stopped it will destroy all coral reefs.

True corals secrete calcium carbonate from the bottom half of the stalk of the individual
animal, or polyp, forming skeletal cups to which the polyps are anchored and into which
they withdraw for protection. In the flattened oral disc at the top of the stalk is an
opening, edged with feathery tentacles and cilia, that is both mouth and anus. At night
the tentacles extend from the cup, seize animal plankton that wash against them, and carry
the food to the mouth. Stinging cells, or nematocysts, on the tentacles can also paralyze

Scientific Classification
Corals belong to the class Anthozoa in the phylum Cnidaria (or Coelenterata). Corals with
eight tentacles make up the subclass Ostocorallia or Alcyonaria. Corals that commonly have
six tentacles or multiples of six belong to the subclass Zoantharia (or Hexacorallia).
Stony, or true, corals belong to the order Scleractinia (or Madreporaria).

Some scleractinians exist as solitary polyps, but the majority are colonial. Colonial
polyps average from 1 to 3 mm (0.04 to 0.12 in) in diameter. They are connected laterally
by tubes that are an extension of the polyps' gastrovascular cavities, and the colony
grows by asexual budding from the base or the oral disc of the polyps. Living polyps build
on the deposits of their predecessors; the wide range of branched or massive forms that
result depends on the species involved.

Corals are animals not plants, but like plants sunlight is the key to their survival. They
need it to power the millions of microscopic algae, called zooxanthellae that live in
their tissues. They co-exist in a mutualistic symbiotic relationship in which the algae
provides the corals with food and oxygen in return for raw materials and a secure place to
live. This teamwork is what allows the reef to survive in nutrient-poor tropical seas.
This relationship is sensitive to many changes in the environment such as cloudy waters or
extreme temperatures. Any stress on the corals can cause them to expel their algae, a
phenomenon known as bleaching (Futurists, 1993). With the algae gone, the coral skeleton
is visible and eventually it dies. Some dead coral will eventually lead to eventual death
of the whole reef.

Threats to the Reefs
There are four environmental factors that effect reef growth: temperature, salinity, water
depth, and wave action. These factors expose the reef to many changes in its environment,
especially since it is located so close to shore. This also makes it hard for all of the
species, which use the coral reef as a habitat to survive. Coral reefs are home to perhaps
one-fourth of all marine species. This in turn effects the entire ecosystem of the ocean.
Pollution by humans have directly or indirectly caused the death of 5%-10% of the world's
living reefs, according to marine biologist Clive Wilkinson of the Australian Institute of
Marine Science. This estimate didn't take into account global warming and ozone depletion
as a factor. Fisheries, oil spills, deforestation, tourists, and even reckless divers, who
may drive their cars into the ocean, cause the pollution, which may eventually lead to
reef death.

The problems, which are becoming even larger issues are the problems of deforestation and
tourism. In the watershed of Bacuit Bay in the Philippines, deforestation increased
erosion into the bay by more that 200 times.(Futurists, 1995) One of the biggest threats
to coral reefs are tourists. Last year alone over 1.2 million tourists visited the Great
Barrier Reef. (Star-Bulletin, 1995) The tourists are not only visitors to the reef,
fisherman, devoted divers and scientists who want to see the enormous reef also visit
frequently. Every year the numbers of visitors increase by 10%. It has brought many
resorts to the area that also want to cash in one the one billion-dollar business. Even
the hotels and motels pollute the reefs with the run off from their drainage and sewage
pipes. This is causing a huge problem in coastal tourism which is the world's fastest
growing industry, worth over $7 billion annually in the Caribbean.(Star-Bulletin, 1995)
Marine Scientists are concerned about how much longer the reef can survive with all these

Global warming and ozone depletion are also major contributors to destruction of the
earth's coral reefs. Global warming is said to cause the effect of bleaching, as mentioned
earlier. This bleaching has just started in the islands of Hawaii. The temperature of the
water in Hawaii is said to have risen over two degrees in just one decade which the
scientists think soon will show the effects in their reefs (Star-Bulletin, 1995). Another
example is the time during 1982-83 better known as the El Nino effect, during which
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