Coral reef types,conditions for growth, importance

1. PABITRA MOHAN SAHOO
ROLLNO:- 22GEOL015
CORAL REEF
DEVLOPEMENT

2. CONTEXT:
1. INTRODUCTION
2. CORAL AND ITS TYPE
3. DEFINATION OF CORAL REEF
4. TYPES OF CORAL REEFS
5. CONDITION FOR GROWTH OF CORAL REEF
6. IMPORTANCE OF CORAL REEF
7. CORAL BLEACHING
8. HUMAN IMPACT ON CORAL REEF

3. INTRODUCTION
• Corals are animals related to sea anemones and jelly fish looking like
flowers.
• some corals are solitary animals with bodies upto 30 cm. in diameter
but most of the more than 500 species are ant sized organisims
crowded into colonies called coral reef.
• coral themselves construct reefs by secreating hard skeletons of
aragonite, a fibrous crystalline form of calcium carbonate.
• corals come under class anthozoa/ actinozoa of the phylum
coelentereta/ cnidaria

4. DEFINATION
• Coral reefs are organically constructed , wave resistant calcareous
topographic structures; these are formed due to accumulation and
compaction of skeletons of lime secreting organisims known as coral
polyps.
• Numerous coral polyps live, at a place, in groups in the form of colony
and form calcareous shells around them which is called test/carapace
which protect them from external injury.
• coral polyps can not survive above water level and hence coral reefs
are always found either upto sea level or below it.
• coral reefs are also be called as rainforest of the oceans”.

5. CORAL POLYPS:
• A coral polyp is an invertebrate that can be no bigger than a pinhead
upto a foot in diameter.
• Each polyp has a saclike body and a mouth that is encircled by
stinging tentacles.
• Coral polyp do not photosynthesize , but have a symbiotic
relationship with microscopic algae( dianoflagellates) of the genus
symbiodinium, commonly referred to as zooxanthellae.
• These organisims live within the polyps tissues and provide organic
nutrients that nourish the polyp in the form of glucose, glycerol, and
amino acid.
• CORALLITE: skeleton of a single polyp.
• CORALLUM: entire skeleton .

7. Varieties of coral:
• Zoantharian: it is also called Hexacoral or Stony coral .
• Alcyonaria: it is also called octacoral.
• Rugosa: it is also called tetracoral.
ZOANTHARIA ALCYONARIA RUGOSA

8. TYPES OF CORAL
• corals can be divided into two major groups:
•
• 1. Hermatypic varieties
2. Ahermatypic varieties
• Hermatypic coral:
• 1. hermatypic coral builds reef found in shallow
tropical sea.
• 2. this type of coral possess zooxanthellae
• Ahermatypic coral:
• 1. these are found in deep, dark cold waters of polar sea.
• 2. this type of coral do not possess zooxanthellae

9. ZOOXANTHELLAE :
• These are the unicellular, golden brown algae( dianoflagellates) that live either
in the water column as plankton or symbiotically inside the tissue of other
organisms.
• The colouration of coral due to the presence of these algae.

10. >
HERMATYPIC VARIETY OF CORAL

11. TYPES OF CORAL REEFS:
• The sub-marine coral reefs are classified:
(1 ) on the basis of nature, shape, and mode of
occurances (2) on the basis of location e.g. tropical coral
reef and marginal belt coral reefs
traditionally they classified as:
1. Fringing reef
2. Barrier reef
3. Atoll

12. FRINGING REEF:
• coral reefs devloped along the continental margins or along the islands arc
called fringing reef
• The seaward slope is steep and vertical while the landward slope is gentle
• These reefs are generally long but narrow in width .
• Fringing reefs are usually attached to the costal land but sometimes there
is a gap between them and land and thus lagoon is formed , such lagoon is
called boat channel.

14. BARRIER REEF:
• Barrier reefs are the largest , most extensive , highest and widest reefs of
all types of coral reefs.
• As the island or margin of the continent subsides, the fringe reef maintain
its positions at the optimum water depth by growing upward , producing
the barrier reef.
• Barrier reefs are seldom found in continuous chain rather they are broken
at many places and thus the lagoon have contact with the open sea and
oceans.
• ex:- great barrier reef , covers about two – third of the costal length of
Queensland province of Australia, is the largest barrier reef of the world.

16. ATOLL:
• A ring of narrow growing corals of horseshoe shape and crowned with
palm trees is called atoll.
• There is a lagoon in the middle of coral ring. the depth of lagoon ranges
beteween 40 to 70 fathoms ( 240 to 420 feet) .
• Faros are the chains of small atolls having shallow small lagoons.

17. > SEQUENTIAL DEVLOPEMENT OF THREE DIFFERENT TYPE OF REEFS

18. CONDITIONS FOR GROWTH OF CORAL REEF:
• Temperature: coral requires temp. between 23 to 25 degree c. for
there growth. minimum temp. must not go below 18 degree c. this
temp. requirement restricts their growth to tropical water between 30
degree lattitude in both the hemisphere.
• Salinity: the range of salinity within which corals grow is 27% . an
exception to this is the red sea where 41% salinity has attracted coral
growth. in high salinity water little amount of lime carbonate is found ,
but lime is the main food for coral polyps.
• Turbidity: turbidity inhibits the growth of corals because corals require
sediment free water. sediments clog the mouth of coral organisims and
inhibiting the symbiotic metabolism by which corals take there oxygen.

19. >:
• Light: the growth of corals takes place in the photic zone. because of
there dependence on light, this zone is not exced 200m. as zooxanthellae
requires light for photosynthesis they must stay in photic zone.
• Ocean current and wave: these are favourable for coral because they
bring necessary food supply for the polyps from distance. currents and
waves also determine the shapes of coral reefs.

20. OF FORMATION OF CORAL REEF:
• subsidence theory of Darwin: Darwin convinced that coral polyps could
grow only in shallow oceanic waters though coral reefs were found at greater
depth where coral polyps could not survive at any cost.
• According to him the land or island involved in the origin and growth of
coral reefs is seldom stationary rather it undergoes gradual subsidence.
• First of all coral polyps flock together along a suitable submarine platform
and grow upward and ultimately reach sea level and fringing reef is formed.
this is formed in stable condition of the land.
• After this the land is subjected to subsidence because of tectonic activity and
thus coral polyps also reach greater depth where they may not survive.
consequently they grow upward and outward at much faster rate and
forming barrier reef. and a lagoon is created in between land and reef.
THEORY

21. >:
• There is further subsidence of the land and the island is completely submerged
under water and a ring of coral reef is formed called it atoll.
• so, according to Darwin fringing reef , barrier reef and atoll are the successive
stages of the devlopement of coral reef.

22. CORAL BLEACHING:
• Coral bleaching refers to loss of algae from the corals resulting into the white
colour which is indicative of death of corals.
• coral bleaching was observed by Alfred mayer off the coast of kenya ,
maldives , andamans and lakshdweep islands in the indian oceans.
• causes: 1. global warming
• 2. sedimentation
• 3. pollutions of sea water by industrial effluents, urban sewage and
oil slicks.
• 4. solar irradiance
• 5. el nino phenomenon ( by increasing temp. of ocean)

23. CORAL BLEACHING:

24. HUMAN IMPACT ON CORAL REEF:
• pollution , overfishing, destructive fishing practice using dynamite or
cyanide, collecting live coral for the aquarium market, mining coral for
building materials, and a warming climate are some of the many ways
that people damage reefs all around the world every day.

26. CONCLUSIONS:
• It may be mentioned that corals also have recovery charecterstics.
• In the past large scale climate change since mesozoic era(230 m.y.
ago) like ice age( pleistocene ice age), fluctuation in solar activities
and several enviromental stresses corals have manage to survive and
recover.
• It is suggested that proper investigations and studies of coral
ecosystems are necessary to understand the view of association
between coral ecosystem, global warming and coral bleaching so that
the corals may be rejuvenated.

27. REFERENCE:
• PHYSICAL OCEANOGRAPHY BY SAVINDRA SINGH
• A BRIEF INTRODUCTION TO OCEANOGRAPHY BY K. SIDDHARTH
• ESSENTIAL OF OCEANOGRAPHY BY ALAN P. TRUJILLO AND HAROLD V.
THURMAN
• TEXT BOOK OF GEOLOGY BY G.B MAHAPATRA
• PRINCIPLE OF ENGEENEARING GEOLOGY BY K.M BANGER