Coral reefs are formed by the accumulation of calcium carbonate skeletons deposited by coral polyps over time. Coral polyps thrive in tropical oceans between 30 degrees north and south latitude where temperatures are between 20-30 degrees Celsius, sunlight levels are sufficient down to around 50 meters depth, and waters have low turbidity with moderate salinity and ocean currents. There are several types of coral reefs including fringing reefs along coastlines, barrier reefs parallel to coastlines separated by lagoons, and ring-shaped atolls which may enclose central lagoons. Coral reefs are most abundant in the tropical Indo-Pacific oceans.

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2. coral reef and atolls are significant submarine features. These are formed due to
deposition and accumulation of skeletons of lime secreting organisms known as
coral polyps. It is basically a type of calcareous rock which is made of skeletons
of minute sea organisms known as polyps.
•These small organisms exact calcium from the sea water to build their skeleton
for protecting their bodies.
•There are 1,000,000 species of coral polyps which only 10% have been studied.
•They have a tendency to live in colonies
•Coral reefs are formed due to formation of one shell upon another along
submarine platforms at suitable depth.
Coral reefs are more diverse than the tropical rain forests
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CONDITION FOR THE GROWH OF CORAL POLYPS.
Coral animals need certain condition of temperature , depth of water ,nature of seawater
for their smooth survival and growth as follows:
1. Location: coral polyps thrive in the tropical oceans confined 30N -30S.
2. Temperature: coral polyps are temperature sensitive shallow sea animals because they
can neither very high temperature nor very low temperature. 20c to 30c requires for the
growth of polyps. Suitable conditions are found in the tropical zone. more than 50 genera of
coral polyps found in the tropical pacific ocean and Indian ocean
3. Depth of seawater: sufficient sunlight requires for the growth of coral polyps. Sunlight
decreases with increasing the depth of seawater. 45-55 meters suitable for the growth of
coral polyps. Sunlight does not favor coral animals directly.
4. Turbidity of Seawater: turbidity means cloudiness of water caused by presence of
suspended materials of inorganic origin. So it is the density of suspended materials which
determines the degree of turbidity of seawater. Higher density of suspended materials and
greater turbidity of seawater. Coral polyps require clean sediment free water as the muddy
water clogs their mouth and they die.

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5. Flux of Fresh water:
coral polyps avoid delta regions, coastal regions because it requires sediment
free water but fresh water is also injurious for the growth of coral animals.
6.Ocean salinity: very high proportion of salinity is injurious for the growth of
coral polyps. because such water contains little amount of calcium carbonates
where lime is the main food of coral polyps. the ocean salinity is ranging
between 27 to 30 is ideal for the growth and development of coral polyps.
7. ocean currents and waves: ocean currents and sea waves are favourable for
coral polyps because they provide necessary food .
8.submarine plateform.:
there should be extensive plateform for the formation of colonies of coral
polyps. it should not be more than 50 fathoms(1 fathom= 6ft/1.8m)

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Hermatype coral Ahermatype coral
They live in group and build their
colonies
They live in isolation as they are
solitary by habit.
They are found in the tropical
regions
They are found in throughout the
world
They don’t find exceed 80 meters They can find shallow to deep water
CORAL ECOLOGY AND CORAL TYPES
The coral ecology means interactions between coral animals
and physical environment. There are different types of coral in
different environment.
(1) Hermatype coral
(2) ahermatype coral

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DISTRIBUTION OF CORAL REEFS
Corals are found in certain patches in the tropical region.basically the coral
reefs are abundantly found in the tropical Indo – Pacific Oceans between 30S -
20N.
55% of world corals are found in the western pacific ocean and 30% of the
coral are found in the Indian ocean.
INDIAN OCEAN:
East coast of Kenya, around Madagascar, south Africa ,western Australia, red
sea , Maldives , Lakshadweep, Andaman and niccobar
PACIFIC OCEAN: Philippines, off southern coast of Japan, Polynesia,
Micronesia, Queensland of Australia
ATLANTIC OCEAN: Caribbean Sea, east coast of Brazil etc.

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TYPE OF CORAL REEFS
The coral reefs are classified in two ways as follows:
1. On the basis of geology , nature , shape and mode of occurrences
which is recognized by Charles Darwin during his study of coral
reef in pacific ocean
(a) FRINGING REEF
(b) BARRIER REEF
(c) ATOLL
2. On the basis of location
(a) Tropical coral reefs in extensive belts
(b) Marginal belts of coral reefs.

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FRINGING REEF
•Coral reef developed along the continental margins or along the
islands is called fringing reef.
•The seaward slope is steep and vertical while landward slope is
gentle
•The upper surface is uneven and corrugated.
•It attaches to the coastal land but sometimes there is gap between
them and land.
•A lagoon is formed between land and reef such lagoon is called
boat channel.
•It is generally long but narrow in width.
Example: Sakau Island, Southern Florida, Methetia etc.

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BARRIER REEF:
•The largest coral reefs off the coastal platforms but parallel to them are called
barrier reef.
•They are the largest, most extensive, highest and widest reef.
•the average slope of the reef is 45 degree but some barrier reefs are
characterized by 15 degree -25 degree
•There is extensive but shallow lagoon between coastal land and barrier reef.
•Barrier reefs are seldom found as continuous chains rather they are broken at
many places thus the lagoon have contact with open sea through tidal inlets.
Example: Great Barrier Reef, located parallel to the east coast of Australia.

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ATOLL
•A ring narrow growing corals of horse shoe shaped and crowned with palm
trees is called atoll
•It is generally found around an island or in elliptical form on a submarine
platform
•There is a lagoon in the middle of coral reef.
•The depth of the lagoon ranges between 40 to 70 fathoms.
Atolls are divided into three types
1. True atoll which are circular reef enclosing a shallow lagoon without island
2. Island atoll having an island in the central part of the lagoon enclosed by
circular reef .
3. Coral island doesn’t have in the beginning but later in island is formed due to
erosion and deposition by marine waves.
Example: Antilles sea, red sea , china sea, Australian sea , Indonesian sea etc.

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