CORAL REEFS ECOSYSTEM

MARINE ECOSYSTEM

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The objective of the blog is to highlight environmental degradation caused by human exploitation.

To know facts about the environment visit the following blogs:
http://www.earth-heritage.blogspot.com/
http://www.earth-jewels.blogspot.com/
http://www.earth-environmental.blogspot.com/
http://www.water-environment.blogspot.com/
http://www.water-studies.blogspot.com/
http://www.marine-corals-blogspot.com/

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RESOURCES FROM CORALS

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The biological productivity of the reefs is very high. We can get from a unit reef area as much fish as from rich fishing grounds like the Peruvian upwelling known for a record anchovy catches. The ornamental fishes from the reefs more colourful and diverse than those from the fresh waters. The demand for ornamental fishes is so high that it is a lucrative industry.

The Philippines is known to export every year aquarium fishes worth millions of dollars.The seaweed from the corals can be used for producing jellies, agar and cosmetics. The villages bordering coral reefs are built only with coral stones and mortar from coral debris,whitewashing is done with coral lime paste.

Industrially the coral sands are rich in CALCIUM and are potential raw materials for the cement industry.

Medically, corals can be used as bone transplants. Either a bone shaped structure can be cut from the coral and use it as a transplant or the skeletal material can be converted to HYDROXYAPATITE, which is the mineral component of the bone. As this forms a bond directly from the bone, it can be used as a bone replacing material; on implantation this promotes new bone growth.

Coral skeletons can also be used in DENTAL APPLICATIONS, as materials to fill in cavities.Soft corals along with other organisms like sponges, bryozoans, sea slugs, and puffer fish, secrete compounds that are bio-active because these compounds are secreted in defence to repulse the enemy and they are basically ANTIBIOTICS but may also prove useful drugs for some human ailments.Some products extracted from sponges and soft corals have shown ANTI-VIRAL PROPERTIES.

Coral reefs protect our coast as they form natural walls that stop strong waves and storm surges form reaching the shores and hence prevents soil erosion.This type of protection is critical to islands because even little of soil erosion can effect them drastically.
Economically, the value of corals in terms of their extractive uses is about 170 billion US $ per year worldwide taking all the reefs together that is about 62 million hectares.

TOURISM to coral reefs is a massive and lucrative industry globally because what the coral reefs offer can offer us by way of aesthetics, recreation, and adventure cannot be matched by any ecosystem. The total economic value of coral reefs along with tourism can be taken to more than 350 billion US $ a year.and the value is ever increasing.

HUMAN ACTIVITIES AFFECTING THE CORALS

CORAL MINING where corals are taken to build houses and produce lime. As a result, large patches or low-lying reefs are totally lost. Industrially,millions of tons of coralline material, including live corals were dredged out killing large portion of the reefs in the process.

POLLUTION: Corals are very sensitive to oil and metal pollution and other onshore activities can kill corals like LOGGING where huge quantities of mud an silt are washed off every monsoon on to the coastal zone which settle on corals and kill them by smothering. Cutting down of mangroves causes the mud to be washed away causing soil erosion and death of near shore corals.

THERMAL POLLUTION, like hot water discharge form the cooling towers of industries or power plants near the reefs, can also kill them.

FACTORS AFFECTING THE GROWTH OF CORALS

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TEMPERATURE:

Plays an important role in the growth and survival of the corals.
They grow well at temperatures greater than 20 degrees centigrade and can thrive even at 35 degrees centigrade as in the RED SEA, PERSIAN GULF or in GULF OF KACHCHH.
Due to this temperature factor and their preference for warm waters, majority of corals are found in the tropical belt.

The other factors affecting the growth of corals are :
Firm substratum to settle like natural surfaces like rocks, coral stones or molluscan shells. Sometimes they grow on metallic structures like hulls of sunken boats and ships.
Salinity of the seawater which contains 35 g of dissolved salt per liter is ideal for the corals to thrive in contrast to fresh water which has only a few mg of dissolved salts.
Water Turbidity caused by high sedimentation affect corals because the skeletons of corals are fixed and open above.
If the sea water is less turbid the corals can clean themselves and survive.
High sedimentation also reduces light penetration in the sea, thus reducing photosynthesis by zooxanthellae and the coral growth.

Corals grow very slowly especially the brain resembling massive corals because the calcium carbonate deposition is a slow process and the growth occurs in all directions. Their growth rate is a centimeter per year.
The branching corals have relatively a faster growth rate and their skeletons are less dense than those of massive ones. The growth rate of branching corals is 18 to 20 centimeters per year.
Growth of the corals is not uniform throughout the year as it depends upon the changing weather conditions.
When the conditions are warm with abundant sunlight corals grow fast, when there is heavy rainfall during monsoon,their growth slows down.

INDICATION OF DARK AND LIGHT BANDS ON CORALS
Dark and white bands present on coral reveal important things like the age of the coral.
When a coral grows fast, it deposits more calcium into the skeleton, which becomes dense and dark and when the growth is slow calcium deposition becomes lighter.
Since seasonal changes, such as those between warm and rainy months occur generally once a year, a dark and light band together would correspond to a one year's growth and hence by counting the number of light and dark bands present on a portion of coral colony the AGE OF THE CORAL can be known.
It is believed some coral colonies are believed to be more than 100 years.

Apart from finding the age of the coral the light and dark bands of the coral also indicate the index of rainfall. This is because the corals contain calcium deposits along with a variety of materials like metals, humic acids and some natural elements like carbon and oxygen.
Among these humic acids come from land sources via the river flow into the sea. So more the rainfall, the more humic acids come with the river flow, the more their presence occurs in the coral skeleton.
When the coral skeleton is looked under the ultra violet light, the presence of humic acids is seen as fluorescent bands.
THE INTENSITY OF FLUORESCENCE is thus an INDEX OF RAINFALL. By knowing the age of the growth band at the location of the fluorescent band, one can deduce whether the monsoon was strong or week at that time.

Light and dark bands are helpful in deducing the fluctuating temperature of the sea water.
At higher temperatures the lighter isotopes of Oxygen escape from the seawater leaving behind the heavier ones.
So, if we find more heavier isotopes of oxygen in the coral skeleton at a particular growth band, then it can be concluded that seawater temperature was higher that year and by how much more it was.
Thus corals act as indicators of PAST CLIMATE CHANGES. CORALS AS PRECIOUS

GEMS/STONES USED IN JEWELLERY.
The RED CORAL, is called 'Corallum rubrum, and is not a reef coral but a stony coral with zooxanthellare. The red colour comes from a natural pigmentation of the skeleton and remains even after the death of the polyp.It is not porous like a reef coral but is dense and compact so, it can be shaped or machined without breakage, and cut into coral beads to be used in jewellery.
The Red coral occurs only in the Mediterranean Sea and off Japan from shallow depths up to 1000 meters. They are collected by skin diving by fisher manor by dragging wooden frames over the seabed and breaking off the branches.Apart from RED CORALS, the BLACK CORALS and THE BLUE CORALS also retain their colour after death.

PREDATORS AND DISEASES SUFFERED BY CORALS
Some fishes like parrot fishes and butterfly fishes bite and nibble the corals. The most dangerous predator of corals is the CROWN-OF-THORN STARFISH as it exclusively feeds on corals. This starfish envelops the whole coral with its arms and sucks out all of the coral tissue, leaving only the bare skeleton.

Corals mainly suffer from two types of disease which are:
THE BLACK BAND DISEASE: It is widely prevalent and this infection is caused by a bacterium wherein the affected coral tissues become blackish and look like a dark band among healthy tissues.
THE WHITE BAND DISEASE: It is less prevalent and causes the affected tissues look like a white band around the lesion.
Recently scientists recorded a new disease known as the PINK LINE DISEASE from the corals in Lakshadweep.The cause of this disease is not known and it is suspected that the mortality associated with the 1998 EL-NINO event has a role in this.

INTRODUCTION

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Nobody knows exactly how many corals are present worldwide. It is believed somewhere around 800 to 1000 species are present.
Sometimes the same coral species is called by different names in different countries. 206 species of corals are known from Indian reefs, with a majority of them occurring in the Andaman and Nicobar Islands.Some coral species are unique to India while others are found in the Oceans of different parts of the world.
Many people think corals are plants because they remain fixed to rocks, are colourful to look at, and many of the branched ones resemble small trees. But actually a coral is a simple animal like the sea anemone we find on the rocky beaches.
The term 'coral' is the skeletal part of the animal while the animal itself is the "polyp". The external surface of the polyp has some special cells called calico blasts that can take dissolved calcium from seawater and construct a solid skeleton.

DIFFERENT SHAPES AND COLOURS OF CORALS
The shape and the size of a coral colony is genetically determined. The common coral shapes seen are as follows:
Massive (stone like)
Foliaceous(leaf like)
Branching(tree like or flower like)
Encrusting(coating like)

At greater depths, the pressure is high and the coral skeleton tends to grow more flat. The growth forms tend to change because the corals are continuously looking out for sunlight.
Sunlight is very important for the growth of a coral because like a plant it prepares its food by the process of photosynthesis.
All corals on the reef have microscopic plants (called Zooxanthellae) living inside their cells. These algae have chlorophyll pigments and produce organic matter by photosynthesis. So the coral has to remain near the surface where sunlight is abundant.
Corals appear coloured due to the presence of algal pigments. In the absence of these pigments the coral tissue would be a transparent layer through which the skeleton can be seen.

CORALS ARE CARNIVOROUS AND NOCTURNAL
Although corals can prepare their own food by photosynthesis they are not totally satisfied hence they catch tiny animals from the seawater and swallow them.This is their main food because whatever they get from the algae is supplementary food.
Some corals can also feed on detritus(dead organic matter) also and some others can take up dissolved organic matter directly from the seawater. The versatility in their feeding habits helps the corals to survive and thrive in oceanic deserts.
Corals are fixed to rocky bases in the reef and hence they cannot move from place to place in search of food like other animals, instead the food comes to them along with the water currents.
Corals feed on tiny microscopic animals called plankton which drift along with currents and when they pass close by the corals catch them with their tentacles, sting them by using their stinging cells and paralyze them by injecting venom and finally swallow them.
Since all corals are nocturnal they are very active in the night when the plankton animals come to the surface layer from deep waters to where they go during the daytime.

STINGING CELLS:-of corals are also called nematocysts which are present in their tentacles and near the mouth.These stinging cells come in at least 20 varieties that is small, big, long and short.They are filled with poisonous substance.

SOLITARY CORALS
Some deep sea corals which do have zooxanthellae do not need light and can live in deep sea and lead a solitary life. These corals are also called asahermatypes and they occur in all latitudes.
Corals which have zooxanthellae need light and hence remain near the surface of the sea. These are called as hermatypic corals, and can be seen only in sub tropical seas and form colonies like coral reefs.