are the "Rainforests" of the ocean. Reefs are ecologically important
ecosystems and have a high biodiversity that serves as a storage bank of rich
genetic resources. They are a source of food and medicine, and they protect the
coast from wave erosion.
of coral reef with typical reef "zones"
Corals are marine animals related
to jellyfish and anemones. Both colonial and solitary corals catch plankton
(microscopic plants and animals) and other suspended food particles with
arm-like tentacles, which feed a centrally located mouth. Most hard corals also
host symbiotic algae, a long-standing and successful partnership. These algae
provide them with an additional food source through photosynthesis. Coral reefs
are formed by corals that secrete hard calcareous (aragonite) exoskeletons,
giving them structural rigidity. These colonial "hard corals" form elaborate
finger-shaped, branching, or moundshaped structures and can create masses of
limestone that stretch for tens or even hundreds of miles.
Although corals have a wide
distribution in the world's oceans, the varieties that form reefs are
typically restricted to relatively shallow, warm tropical waters between
latitudes 30 north and 30 south. Clean, clear water is essential to their
health. Once coral larvae settle on a hard substrate and become established,
colonies can arise if conditions are suitable for growth. Given enough time,
coral colonies become thickets. As coral thickets build upward on the skeletal
remains of older colonies, a reef is established. Today, richly diverse coral
reefs are found in the tropics along coastlines, on the margins of volcanic
islands, and as isolated coral atolls.
There are two distinct regions in
which coral reefs are primarily distributed: the Wider Caribbean
(Atlantic Ocean) and the Indo-Pacific (from East Africa and the Red Sea to the
Central Pacific Ocean).
The diversity of coral is far
greater in the Indo-Pacific, particularly around Indonesia, the Philippines,
and Papua New Guinea. Many other groups of marine fauna show similar
patterns, with a much greater diversity in the Indo-Pacific region.
Although they possess a
smaller number of species the corals of the Atlantic are still unique, with
few common species between the two regions .
majority of reef building corals are found within tropical and subtropical
waters. These typically occur between 300 north and 300
south latitudes. The red dots on this map show the location of major stony coral
reefs of the world. Credit:NOAA
Science from Outer Space to Inner Space
Coral reefs are found in about 100 countries. Coral
Reefs are home to
over 25 percent of all marine life and are among the world's most fragile and
endangered ecosystems. In the last few decades over 35 million acres of Coral
Reefs have been
Reefs off of 93
countries have been damaged . When corals are stressed by high temperature,
ultraviolet light or other environmental changes, they lose their symbiotic
algal cells, and appear white (the white skeleton is actually visible through
the transparent tissue). Depending on the intensity and duration of the stress,
the corals may recover or die.
If the present rate of destruction continues, 70% of the world's coral reefs will be destroyed within the
next few decades.
Climate change will destroy the
world's great coral reefs within a century, according to a report by German and
Australian marine scientists.Researchers say
governments must take action now to reduce the emissions of gases such as carbon
dioxide, which are thought to be behind a rise in average global temperatures.
rise in temperature can bleach coral like this
The scientists combined their
coral expertise with the latest climate models to project what is likely to
happen to the world's greatest reefs if global warming remains unchecked. Their
study suggests the unique marine environments will increasingly become victim to
a process known as coral bleaching.
A slight rise in maximum water
temperatures - only one to two degrees - can stress the corals. This causes them
to expel the microscopic organisms, known as zooxanthellae, which color their
tissues and provide them with essential nutrients.
If the zooxanthellae do not
return, the corals will die. In 1998 every reef
system in the world's tropical oceans were affected by some degree of bleaching.
The report says the frequency and intensity of bleaching is set to rise.
The report's lead author is
Professor Ove Hoegh-Guldberg, an expert on coral bleaching at Sydney University.
reefs could be eliminated from most areas of the world by 2100, Even the
world's largest reef - the Great Barrier Reef off Australia - could be dead
within 30 years unless measures are taken now to slow climate change.
is a general term used to describe a group of cnidarians, which indicates the
presence of skeletal material that is embedded in the living tissue or encloses
the animal altogether. -National Oceanic and Atmospheric Administration, U.S.
Dept. of Commerce. "Glossary of Coral Reef Terminology."
themselves are tiny animals which belong to the group cnidaria (the
"c" is silent). Other cnidarians include hydras, jellyfish, and sea
anemones. Corals are sessile animals, meaning they are not mobile but stay fixed
in one place.They feed by reaching out with tentacles to catch prey such as
small fish and planktonic animals.
are anthozoans, the largest class of organisms within the phylum Cnidaria.
Comprising over 6,000 known species, anthozoans also include sea fans, sea
pansies and anemones. Stony corals (scleractinians) make up the largest order of
anthozoans, and are the group primarily responsible for laying the foundations
of, and building up, reef structures. For the most part, scleractinians are
colonial organisms composed of hundreds to hundreds of thousands of individuals,
live in colonies consisting of many individuals, each of which is called polyp.
They secrete a hard calcium carbonate skeleton, which serves as a uniform base
or substrate for the colony. The skeleton also provides protection, as the
polyps can contract into the structure if predators approach. It is these hard
skeletal structures that build up coral reefs over time. The calcium carbonate
is secreted at the base of the polyps, so the living coral colony occurs at the
surface of the skeletal structure, completely covering it. Calcium carbonate is
continuously deposited by the living colony, adding to the size of the
structure. Growth of these structures varies greatly, depending on the species
of coral and environmental conditions-- ranging from 0.3 to 10 centimeters per
year. Different species of coral build structures of various sizes and shapes
("brain corals," "fan corals," etc.), creating amazing
diversity and complexity in the coral reef ecosystem. Various coral species tend
to be segregated into characteristic zones on a reef, separated out by
competition with other species and by environmental conditions.
corals are made up of hundreds of thousands individual polyps like this one.
Many stony coral polyps range in size from one to three millimeters in diameter.
Anatomically simple organisms, much of the polyp's body is taken up by a
stomach filled with digestive filaments. Open at only one end, the polyp takes
in food and expels waste through its mouth. A ring of tentacles surrounding the
mouth aids in capturing food, expelling waste and clearing away debris. Most
food is captured with the help of special stinging cells called nematocysts
which are inside the polyp' outer tissues, which is called the epidermis.
Calcium carbonate is secreted by reef-building polyps and forms a protective cup
called a calyx within which the polyps sits. The base of the calyx upon which
the polyp sits is called the basal plate. The walls surrounding the calyx are
called the theca. The coenosarc is a thin band of living tissue that connect
individual polyps to one another and help make it a colonial organism.
As members of the phylum Cnidaria,
corals have only a limited degree of organ development. Each polyp consists of
three basic tissue layers: an outer epidermis, an inner layer of cells lining
the gastrovascular cavity which acts as an internal space for digestion, and a
layer called the mesoglea in between
diagram above shows the anatomy of a nematocyst cell and its
"firing" sequence, from left to right. On the far left is a
nematocyst inside its cellular capsule. The cell's thread is coiled
under pressure and wrapped around a stinging barb. When potential prey
makes contact with the tentacles of a polyp, the nematocyst cell is
stimulated. This causes a flap of tissue covering the nematocyst-the
operculum-to fly open. The middle image shows the open operculum,
the rapidly uncoiling thread and the emerging barb. On the far right
is the fully extended cell. The barbs at the end of the nematocyst are
designed to stick into the polyp's victim and inject a poisonous
liquid. When subdued, the polyp's tentacles move the prey toward its
mouth and the nematocysts recoil back into their capsules.
polyps share two basic structural features with other members of their phylum.
The first is a gastrovascular cavity that opens at only one end. At the opening
to this cavity, commonly called the mouth, food is consumed and some waste
products are expelled. A second feature all corals possess is a circle of
tentacles, extensions of the body wall that surround the mouth. Tentacles help
the coral to capture and ingest plankton for food, clear away debris from the
mouth, and act as the animal's primary means of defense.
polyps have structurally simple body plans, they possess several distinctive
cellular structures. One of these is called a cnidocyte-a type of cell unique
to, and characteristic of, all cnidarians. Found throughout the tentacles and
epidermis, cnidocytes contain organelles called cnidae, which include
nematocysts, a type of stinging cell. Because nematocytes are capable of
delivering powerful, often lethal toxins, they are essential to capturing prey,
and facilitate coralline agonistic interactions
Most corals, like other cnidarians,
contain a symbiotic algae called zooxanthellae, within their gastrodermal cells.
The coral provides the algae with a protected environment and the compounds
necessary for photosynthesis. These include carbon dioxide, produced by coral
respiration, and inorganic nutrients such as nitrates, and phosphates, which are
metabolic waste products of the coral. In return, the algae produce oxygen and
help the coral to remove wastes. Most importantly, they supply the coral with
organic products of photosynthesis. These compounds, including glucose,
glycerol, and amino acids, are utilized by the coral as building blocks in the
manufacture of proteins, fats, and carbohydrates, as well as the synthesis of
calcium carbonate (CaCO3). The mutual exchange of algal photosynthates and
cnidarian metabolites is the key to the prodigious biological productivity and
limestone-secreting capacity of reef building corals.
(Courtesy Scott R. Santos, of the
State University of New York at Buffalo)
often are critical elements in the continuing health of reef-building corals. As
much as 90% of the organic material they manufacture photosynthetically is
transferred to the host coral tissue . If these algal cells are expelled by the
polyps, which can occur if the colony undergoes prolonged physiological stress,
the host may die shortly afterwards. The symbiotic zooxanthellae also confers
its color to the polyp. If the zooxanthellae are expelled, the colony takes on a
stark white appearance, which is commonly described as "coral bleaching"
Coral reefs are among the oldest ecosystems on Earth.
Coral reefs are the largest living structure on the planet.
Although coral reefs cover less than 1% of the Earth's surface, they are
home to 25% of all marine fish species.
500 million people rely on coral reefs for their food and livelihoods.
Coral reefs form natural barriers that protect nearby shorelines from the
eroding forces of the sea, thereby protecting coastal dwellings,
agricultural land and beaches.
Without the existence of coral reefs, parts of Florida would be under water.
Coral reefs have been used in the treatment of cancer, HIV, cardiovascular
diseases and ulcers.
Corals' porous limestone skeletons have been used for human bone grafts.
It is estimated that coral reefs provide $375 billion per year around the
world in goods and services.
If the present rate of destruction continues, 70% of the world's coral reefs
will be destroyed by the year 2050.
Report States Half of U.S. Coral Reefs In "Poor" or
"Fair" Condition -Click Here
Reef Relief founders Craig and DeeVon Quirolo retired from the grassroots organization last July, only to begin an effort to provide an online resource on coral reefs. Their new website provides all the award-winning educational tools, grassroots strategies, project reports and images of coral reefs assembled during their work over the past 23 years in the Florida Keys and throughout the Caribbean protecting coral reefs. You can find it at
NOAA, NASA, Reef Check, UNEP, Reef Relief, Australian Government, University of
Texas,Great Barrier Reef Marine Park Authority