DR. ABHIJIT MITRA EXHIBITS---CORAL REEF- THE UNDERWATER PARADISE

1. CORAL REEFS: Teeming with life

2. CORAL REEF: AN OVERVIEWCORAL REEF: AN OVERVIEW
Coral reefs, the rain forest of the ocean, occupy only
0.2% of the total ocean basin, but support not less than
25% species of the ocean. The reefs sustain the most
luxuriant and complex of all benthic communities. They
are often regarded as the oases of the ocean. The Great
Barrier Reef, the largest coral reef of the planet Earth
stretches more than 2000 km from New Guinea
southward along the east coast of Australia. The reefs
are constructed and promoted by corals, which are
colonial animals and whose individual members are
called polyps
Coral reefs, the rain forest of the ocean, occupy only
0.2% of the total ocean basin, but support not less than
25% species of the ocean. The reefs sustain the most
luxuriant and complex of all benthic communities. They
are often regarded as the oases of the ocean. The Great
Barrier Reef, the largest coral reef of the planet Earth
stretches more than 2000 km from New Guinea
southward along the east coast of Australia. The reefs
are constructed and promoted by corals, which are
colonial animals and whose individual members are
called polyps

3. SOFT CORALS like SEA FANS (Gorgonia sp.)

4. CORAL POLYPCORAL POLYP
A coral polyp is very similar to a tiny seaA coral polyp is very similar to a tiny sea
anemone possessing stinging tentacles, butanemone possessing stinging tentacles, but
unlike the anemone, a coral polyp extractsunlike the anemone, a coral polyp extracts
calcium carbonate from the water and buildscalcium carbonate from the water and builds
within its tissues a skeletal cup of calcareouswithin its tissues a skeletal cup of calcareous
material. Large numbers of polyps grow togethermaterial. Large numbers of polyps grow together
in colonies of delicately branched forms orin colonies of delicately branched forms or
rounded masses. Corals are very slowly growingrounded masses. Corals are very slowly growing
organisms; some species grow less than 1 cm inorganisms; some species grow less than 1 cm in
a year while others add up to 5 cm each year.a year while others add up to 5 cm each year.
The same coral may be found in different shapesThe same coral may be found in different shapes
and sizes, depending on the depth andand sizes, depending on the depth and
wave action of the area.wave action of the area.

6. FORMATION OF A CORAL COLONY

7. ZOOXANTHELLAE: A TRUEZOOXANTHELLAE: A TRUE
FRIEND OF CORAL POLYPFRIEND OF CORAL POLYP
Within the tissues of the coral polyps, single cellWithin the tissues of the coral polyps, single cell
dinoflagellate algae calleddinoflagellate algae called zooxanthellaezooxanthellae are present.are present.
Polyps and zooxanthellae have symbiotic relationship inPolyps and zooxanthellae have symbiotic relationship in
which the coral provides the algal cells with a protectedwhich the coral provides the algal cells with a protected
environment, carbon dioxide and nutrients (like nitrateenvironment, carbon dioxide and nutrients (like nitrate
and phosphate) and the algal cells by the process ofand phosphate) and the algal cells by the process of
photosynthesis return oxygen, remove wastes andphotosynthesis return oxygen, remove wastes and
produce carbon compounds, which help to nourish theproduce carbon compounds, which help to nourish the
coral. Some coral species receive as much as 60% ofcoral. Some coral species receive as much as 60% of
their nutrition from the algae. Zooxanthellae also causetheir nutrition from the algae. Zooxanthellae also cause
the coral to produce more calcium carbonate andthe coral to produce more calcium carbonate and
increase the growth of their calcareous skeleton.increase the growth of their calcareous skeleton.

8. REQUIREMENT FOR CORALREQUIREMENT FOR CORAL
REEF FORMATIONREEF FORMATION
The reef building corals of tropical regions haveThe reef building corals of tropical regions have
specialized requirements likespecialized requirements like warm, clear, shallow, cleanwarm, clear, shallow, clean
water and a firm substratum to which they can attachwater and a firm substratum to which they can attach..
The growth of the corals is restricted to tropical watersThe growth of the corals is restricted to tropical waters
between 30between 30oo
N and 30N and 30oo
S where the temperature usuallyS where the temperature usually
ranges between 20ranges between 20oo
C to 25C to 25oo
C. Waters at depths greaterC. Waters at depths greater
than 50 to 100 meters are too cold for considerablethan 50 to 100 meters are too cold for considerable
secretion of calcium carbonate. Perhaps because of thissecretion of calcium carbonate. Perhaps because of this
reason, most of the Caribbean corals are found in thereason, most of the Caribbean corals are found in the
upper 50 m of lighted zone, whereas Indian and Pacificupper 50 m of lighted zone, whereas Indian and Pacific
corals are found at depths of 150 m in the morecorals are found at depths of 150 m in the more
transparent water of these oceans.transparent water of these oceans.

9. CORAL REEF: A HOTSPOT OFCORAL REEF: A HOTSPOT OF
BIODIVERSITYBIODIVERSITY
Coral reefs are ecologically important ecosystems with richCoral reefs are ecologically important ecosystems with rich
biodiversity. They support complex assemblages of manybiodiversity. They support complex assemblages of many
different types of plants and animals having intensedifferent types of plants and animals having intense
competition for space and food. Globally, coral reefscompetition for space and food. Globally, coral reefs
comprise little more than 1% of total continental shelf areacomprise little more than 1% of total continental shelf area
(Groombridge and Jenkins, 2002), but they are among the(Groombridge and Jenkins, 2002), but they are among the
most diverse of the world’s ecosystems. It is estimated thatmost diverse of the world’s ecosystems. It is estimated that
about 793 species of scleractinian corals are present world-about 793 species of scleractinian corals are present world-
wide (Veron, 2000) of which 719 occur in the Indo-Westwide (Veron, 2000) of which 719 occur in the Indo-West
Pacific region. Very few species of any taxa are found in bothPacific region. Very few species of any taxa are found in both
the Indo-Pacific coral reef area and Caribbean reef areathe Indo-Pacific coral reef area and Caribbean reef area
(Burke(Burke et alet al., 2001). It has been reported that the coral., 2001). It has been reported that the coral
species richness of Indian Ocean rim countries is very similarspecies richness of Indian Ocean rim countries is very similar
to those in the Pacific Ocean with both of these regionsto those in the Pacific Ocean with both of these regions
having significantly greater coral diversity than the Atlantic.having significantly greater coral diversity than the Atlantic.
Countries with large coral diversities such as Indonesia (443),Countries with large coral diversities such as Indonesia (443),
Australia (428) and Thailand (238) border both the Indian andAustralia (428) and Thailand (238) border both the Indian and
Pacific Oceans, thus increasing thePacific Oceans, thus increasing the
apparent diversity of both.apparent diversity of both.

10. Boxer crab (Boxer crab (DromidiaDromidia sp.)sp.)

11. Reef dwelling crustacean: mantis shrimp

12. Reef Octopus
Sand crab

13. Soap fishSoap fish
Produces a toxic mucous when disturbed
(protective adaptation)

14. Trunk fishTrunk fish
Tough leather like exterior membrane

15. Tiger cowryTiger cowry

16. ECOLOGICAL IMPORTANCE OFECOLOGICAL IMPORTANCE OF
CORAL REEFCORAL REEF
The coral reef community has diverse ecological importance. One ofThe coral reef community has diverse ecological importance. One of
the most important components of coral reef community is the coral.the most important components of coral reef community is the coral.
Productivity of these reefs is high due to their symbiotic associationProductivity of these reefs is high due to their symbiotic association
with zooxanthellae and the efficient recycling of nutrients. Thesewith zooxanthellae and the efficient recycling of nutrients. These
corals check erosion and are closely associated with diversecorals check erosion and are closely associated with diverse
organisms such as brachyuran crabs (organisms such as brachyuran crabs (e.ge.g.,., TrapeziaTrapezia spp.,spp., TetraliaTetralia
sp.,sp., CymoCymo spp.spp. Domecia glabraDomecia glabra), gastropods (e.g.,), gastropods (e.g., CoralliophilaCoralliophila
violaceaviolacea,, OuoyolaOuoyola sp.) and fishes (sp.) and fishes (e.ge.g.,., AbudefdufAbudefduf spp.,spp., DascyllusDascyllus
spp.). Turtles consume sea grasses in the reefs. In addition, coralspp.). Turtles consume sea grasses in the reefs. In addition, coral
reefs are nursery grounds for many fishes and habitat for rarereefs are nursery grounds for many fishes and habitat for rare
species. Corals grow very slowly and its gradual damage will notspecies. Corals grow very slowly and its gradual damage will not
only affect the biodiversity of the area, but will also pose an adverseonly affect the biodiversity of the area, but will also pose an adverse
impact on the recruitment and yield of fisheries.impact on the recruitment and yield of fisheries.

18. ECONOMIC VALUE OF CORALSECONOMIC VALUE OF CORALS
Corals have been exploited for commercial purposes. TheirCorals have been exploited for commercial purposes. Their
aesthetic value makes them costly souvenirs for tourists. Corallineaesthetic value makes them costly souvenirs for tourists. Coralline
boulders (mainlyboulders (mainly PoritesPorites sp.) have been used as cheap substitutesp.) have been used as cheap substitute
for construction of houses. Coral reefs host many organisms thatfor construction of houses. Coral reefs host many organisms that
are of commercial importance and many of them are found on theare of commercial importance and many of them are found on the
accessible reef flats. The algae present on the coral reef system areaccessible reef flats. The algae present on the coral reef system are
often utilized for the extraction of agar and algin.often utilized for the extraction of agar and algin.
Holothurians, being member of the reef community have beenHolothurians, being member of the reef community have been
exploited in India for the production ofexploited in India for the production of beche-de-merbeche-de-mer, an industry, an industry
introduced by the Chinese more than a thousand year ago (Hornell,introduced by the Chinese more than a thousand year ago (Hornell,
1917). The product containing about 35 – 50% digestible proteins1917). The product containing about 35 – 50% digestible proteins
imparts a flavour to soup. Though there is an internal market forimparts a flavour to soup. Though there is an internal market for
beche-de-merbeche-de-mer, foreign exchange equivalent to one crore Rupees is, foreign exchange equivalent to one crore Rupees is
earned every year (James and James, 1994). This industry hasearned every year (James and James, 1994). This industry has
been mainly restricted to Gulf of Mannar and the Palk Bay and hasbeen mainly restricted to Gulf of Mannar and the Palk Bay and has
been facing a crisis due to declining stocks.been facing a crisis due to declining stocks.

19. ECONOMIC VALUE (Contd…)ECONOMIC VALUE (Contd…)
Extraction of bioactive substances is anotherExtraction of bioactive substances is another
important economic benefit obtained from coralimportant economic benefit obtained from coral
reef organisms. The puffer fishesreef organisms. The puffer fishes TetradonTetradon spp.spp.
contain tetrodotoxin, which is a neurotoxin. Manycontain tetrodotoxin, which is a neurotoxin. Many
of the compounds extracted from coral reefof the compounds extracted from coral reef
associated species, useful to the pharmaceuticalassociated species, useful to the pharmaceutical
industry, have been identified (Kennish, 1989)industry, have been identified (Kennish, 1989)
and some of them are being commerciallyand some of them are being commercially
marketed. Using biotechnological techniques,marketed. Using biotechnological techniques,
these compounds can be mass-produced in thethese compounds can be mass-produced in the
laboratory without exploiting the naturallaboratory without exploiting the natural
population.population.

20. Types of coral reefsTypes of coral reefs
On the basis of the structure and theirOn the basis of the structure and their
relationship to the underlying geologicrelationship to the underlying geologic
features, coral reefs can be divided intofeatures, coral reefs can be divided into
three categories. They are: Fringing reefs,three categories. They are: Fringing reefs,
Barrier reefs and Atolls.Barrier reefs and Atolls.

21. Fringing reefsFringing reefs
These are found very close to or nearThese are found very close to or near
the newly formed volcanic islands as wellthe newly formed volcanic islands as well
as surrounding the continentalas surrounding the continental
landmasses. They are located directlylandmasses. They are located directly
offshore and project outward to the sea.offshore and project outward to the sea.
e.g.,e.g., the Caribbean reef.the Caribbean reef.

22. Barrier reefsBarrier reefs
These reefs act as barrier separated by aThese reefs act as barrier separated by a
lagoon from the landmass, with which they arelagoon from the landmass, with which they are
associated. Those surrounding volcanicassociated. Those surrounding volcanic
islands are formed from subsiding islands withislands are formed from subsiding islands with
fringing reefs. The lagoon forms between thefringing reefs. The lagoon forms between the
island and the reef. The largest barrier reef isisland and the reef. The largest barrier reef is
the Great Barrier Reef of Australia, which runsthe Great Barrier Reef of Australia, which runs
over 2,000 km along the north-easternover 2,000 km along the north-eastern
coast of Australia to New Guinea. It is so largecoast of Australia to New Guinea. It is so large
that it is visible from space shuttle. The secondthat it is visible from space shuttle. The second
largest barrier reef is located in the Caribbeanlargest barrier reef is located in the Caribbean
Sea off the coast of Belize.Sea off the coast of Belize.

23. AtollsAtolls
These reefs are somewhat circular in shape with aThese reefs are somewhat circular in shape with a
centrally located lagoon. According to Darwin, they arecentrally located lagoon. According to Darwin, they are
formed in areas where barrier reefs subside below seaformed in areas where barrier reefs subside below sea
level, whereas according to Alexander Agassiz they arelevel, whereas according to Alexander Agassiz they are
formed on the top of the cones of submergedformed on the top of the cones of submerged
volcanoes, leaving only the reef around a centralvolcanoes, leaving only the reef around a central
lagoon. But in any of the case, the lagoon remainslagoon. But in any of the case, the lagoon remains
connected to the open sea by breaks in the reef. Overconnected to the open sea by breaks in the reef. Over
time, the reefs may become eroded or exposed to windtime, the reefs may become eroded or exposed to wind
action or waves. These physical processes sometimesaction or waves. These physical processes sometimes
give rise to formation of islands surrounding thegive rise to formation of islands surrounding the
lagoons, which is perhaps the depositional feature oflagoons, which is perhaps the depositional feature of
sand carried by the wind or wave action. More than 300sand carried by the wind or wave action. More than 300
atolls are present in and around Pacific and Indianatolls are present in and around Pacific and Indian
Ocean whereas 10 atolls are present in Atlantic OceanOcean whereas 10 atolls are present in Atlantic Ocean
as the water is too cool or turbid.as the water is too cool or turbid.

24. Fringing reef
Atoll
Barrier reef

25. Distribution: TROPICS & SUB TROPICS

26. FEW SUGGESTIVE QUESTIONSFEW SUGGESTIVE QUESTIONS
State the criteria for coral reef formationState the criteria for coral reef formation
and discuss the mechanism of reefand discuss the mechanism of reef
formation.formation.
Why coral reefs are referred to as the “rainWhy coral reefs are referred to as the “rain
forest of ocean”?forest of ocean”?
State the ecological and economic valueState the ecological and economic value
of coral reefs.of coral reefs.
What are the different types of coral reefs?What are the different types of coral reefs?
Define polyp.Define polyp.