Coral reefs are vital marine ecosystems formed by coral polyps that build limestone structures, providing habitat for diverse marine life. There are two main types of corals, hermatypic and ahermatypic, which have different environments and relationships with algae. Coral reefs face threats from human activities and climate change, leading to issues like coral bleaching and ecological imbalance.

1. Coral Reef
By Dr. Lopamudra Samantaray
Asst. Professor
Utkal University​

2. Polyp
• Polyp has a tubular body with a mouth surrounded by
tentacles at one end.
• Sessile, primitive
• Another end is blind and attached to the substratum.
• Concerned with feeding, protection
• Ex - corals

3. Medusa
• Medusa has a bowl or umbrella shaped body with
marginal tentacle and mouth is centrally located
in a projection called manubrium on the ventral
concave surface.
• Evolved from polyp
• Medusae are generally motile
• Ex- Jellyfishes

4. 4
What are Coral Reefs?
• Coral reefs are warm, clear,
shallow ocean habitats that
are rich in life.
• The reef's massive structure
is formed from coral polyps,
tiny animals that live in
colonies; when coral polyps
die, they leave behind a hard,
stony, branching structure
made of limestone.

5. What should you know about corals?
• They are animals
• Plants live inside of them
• Two kinds
• Soft corals
• Hard corals (These build
reefs!)
• They are made of tiny
polyps (which look like upside-
down jellyfish)

6. Hard Corals
The Reef Builders
• Polyps build hard limestone
cups around their bases
• The cups cement together
to make a coral colony
• Reefs are made of
hundreds of hard coral
colonies next to and on top
of each other

7. What’s a Polyp?
• A coral polyp is an invertebrate
that can no bigger than a
pinhead up to a foot in diameter
• Each polyp has a sac like body
and a mouth that is encircled by
stinging tentacles.
• Coral polyp do not
photosynthesize, but have a
symbiotic relationship with
microscopic algae, referred as
zooxanthellae.

8. What’s a Polyp?
• These organisms live within the
polyp 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
• Columella

9. • Zoantharian: it is also
called hexacoral or stony
coral
• Alcyonaria: it is also called
octacoral
• Rugosa: a tetracoral
Zoantharian
Rugosa
Alcyonaria
Varieties of coral

10. Corals divided into 2 major groups
1. Hermatypic varieties
• These coral builds found in
shallow tropical sea
• Possess zooxanthellae
2. Ahermatypic coral
• Found in deep, dark cold waters
of polar sea
• Don’t possess zooxanthellae
Hermatypic
Ahermatypic

11. 11
Zooxanthellae
• These are the unicellular,
golden brown algae 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 alage

12. Symbiosis:
So Happy Together
• Two organisms living together
and helping each other is called
symbiosis.
• Zooxanthellae make oxygen,
remove the polyp’s wastes,
and make food for the polyp
from photosynthesis.
• Coral polyps protect the
zooxanthellae, release CO2,
and provide it with necessary
nutrients from their own
waste.

13. 13
Coral reefs are important to our future. They are:
• home and nursery for almost a million fish and
other species, many that we rely on for food;
• some of the earth's most diverse living
ecosystems;
• important protection for coastal communities
from storms, wave damage and erosion;
• full of new and undiscovered biomedical
resources that we've only just begun to explore.
• Reefs are a recreational resource for local
people and for tourism.
Why should we care about
coral reefs?

14. Types of coral reefs
1. Fringing reefs
• Coral reefs developed along
the continental margins or
along islands arc called
fringing reef.
• The seaward slope is stiff and
vertical while the landward
slope is gentle
• Generally long but narrow in
width
• Usually attached to the coastal
land but sometimes lagoon is
formed (Boat channel)
14

15. Types of coral reefs
2. Barrier reef
• Largest, extensive,
highest and widest reefs
• 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.
• Ex- Great barrier reef
(Largest)
15

16. Types of coral reefs
3. Atoll
• A ring of narrow growing corals of
horseshoe shape and crowned with
palm tress is called atoll
• A lagoon in the middle of the coral
ring. Depth of lagoon between 240
t0 420 ft.
• Faros are the chain of small atolls
having shallow small lagoons
Presentation title 16

17. Types of coral reef
17

18. Conditions for the growth
of coral reefs
• Temperature
• Salinity
• Turbidity
• Light
• Ocean current and wave
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19. Theory of formation of
coral reef
Subsidence theory of Darwin
Coral polyps could grow only in shallow oceanic water, and
could not survive at greater depth.
Coral polyps flock together along suitable submarine
platform and grow upward and ultimately reach sea level
and fringing reef formed.
Because of tectonic activity, coral polyps reach greater
depth and may not survive. Subsequently grow upward and
outward and form barrier reef and a lagoon created
between land and reef
19

20. Theory of formation of
coral reef
The land and the island is completely submerged under water
and ring of coral reef is formed called atoll.
So barrier reef and atoll are the successive stages of the
development of coral reef
Glacial-control theory of Daly
With lowering of ocean level, flat platforms exposed.
Temperature become favorable and corals grow
Reef 20
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21. Coral bleaching
Loss of algae from corals
and results white color
(death of coral)
Causes
1. Global warming
2. Sedimentation
3. Pollution of sea water
by industrial effluents,
urban wastage and oil
clicks
21

22. Coral bleaching
Loss of algae from
corals and results white
color (death of coral)
Causes
4. Solar irradiance
5. By increasing temp.
of ocean
22

23. Human impact on coral reefs
• Pollution, overfishing,
destructive fishing 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
23
coral reef disturbance and recovery at
North Reef in Capricorn-Bunkers on
the Great Barrier Reef

24. Thank you
References
• Animal Diversity (R.L Kotpal); First edition Rastogi publication (2018)
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