Growth of coral reefs is affected by both abiotic and biotic factors. Abiotic factors that influence coral reef growth include latitude, temperature, light, salinity, turbidity, wave action, aerial exposure, and the need for a firm substrate. Biotic factors include mutualistic relationships between corals and zooxanthellae, as well as competition and predation between coral species. Both natural stresses such as storms, disease, and river runoff, as well as human impacts like pollution, sedimentation, and climate change threaten the growth and survival of coral reefs.

1. FACTORS AFFECTING THE GROWTH OF CORAL
REEFS
VIJAYKUMAR, M.E,
DFK – 1304
I PhD, Dept. of FRM

2.  Latitude
 Temperature
 Light
 Salinity
 Turbidity &
sedimentation
 Wave action
 Aerial exposure
 Firm substrata
Growth
Abiotic factors Biotic factors
Species
interactions
(mutualism,
competition,
predation
Growth of reef corals is affected by both abiotic and biotic factors

4. LATITUDE
High calcification rates are limited to warm
waters. Consequently, coral reefs are restricted
to tropical seas, generally between 250 N and
250 S latitudes.

5. Temperature
Reef building corals cannot tolerate water
temperatures of less than180C (except as in
the Florida Keys of the United States),
although some corals tolerate temperatures
of up to 400C , optimum growth usually
occurs between 230C and 290C.

6. Light
After temperature, light is probably the most
important limiting factor to well-developed
coral reefs because of the symbiosis
between hermatypic scleractinian corals
and zooxanthellae
Since light intensity decreases exponentially
with depth, active reef building rarely occurs
below about 20-30m.

7. PAR

8. Salinity
Hermatypic corals seem to require open-ocean salinity
Well-developed reefs are not generally found in estuarine
or excessively hypersaline conditions(Persian Gulf reefs,
however, develop in salinities of more than 40ppt)
 The absence of reefs along much of the tropical coastline
of the Atlantic coast of South America is due to the
influence of large rivers such as the Amazon and Ornico
High rains, resulting in excessive runoff, cause extensive
damage to corals close to river mouths

9. Turbidity & Sedimentation
High turbidity and sedimentation rates strongly
inhibit reef growth.
Turbidity reduces light penetration whilst, settling
silt particles smother the feeding structures of the
delicate coral polyps.
Rivers carry a large suspended sediment load to
the coastal areas periodically, which is
detrimental to corals

10. Wave action
Coral reefs thrive in regions of strong water
movement.
 Wave action prevents sedimentation and keeps
the water well oxygenated.
 Although the rigid calcareous skeletons of most
hermatypic corals are particularly resistant to
wave shock, severe storms do occasionally
cause extensive damage.
Storm damage can, in fact, be a mechanism of
coral dispersal, for pieces of living colonies
transported to new sites may survive to cement to
the bottom and establish a permanent new colony

11. Aerial exposure
Corals are unable to withstand prolonged aerial
exposure and rarely grow much above the low
spring-tide level.
The upward growth of a reef is restricted to the
level of lowest tides, as exposure to air for
more than several hours kills corals

12. FIRM SUBSTRATA
 New reefs are initially formed by the
attachment of meroplanktonic coral larvae
(planulae) to a hard substrate, so a firm
platform is always necessary for
establishment and growth

14. MUTUALISM
 Symbiotic relationships are especially important in
structuring coral-reef communities.
 between Zooxanthellae, coral polyp
Carbondioxide, ammonium phosphate
Oxygen, photosynthate

15. COMPETITION
 Competition for limited living space on coral reefs is
potentially severe
 Fast - growing branching corals are capable of
overtopping slow – growing encrusting or massive
forms
 Coexistence is facilitated however by the combined
effects of physical disturbance (storms) and
aggressive behaviour (tissue necrosis) of the
slower – growing species

16. PREDATION
 The major groups of coral predators are star fish,
sea urchins and fish
 Acanthaster planci
 giant triton (Charonia tritonis)
 Fish species that feed directly on coral polyps
(puffer fish, file fish, trigger fish)
 Surgeon fish, parrot fish digests the algae and
endolithic fauna

17. NATURAL SOURCES OF STRESS ON CORAL
REEFS
intense storms
El Niño
disease
volcanic eruptions
predator population explosions
natural stream and river runoff
exceptionally low tides

18. STORM WAVE DAMAGE
Before After

19. STORM DAMAGE

20. CROWN-OF-THORNS OUTBREAKS

21. STREAM AND RIVER RUNOFF

22. LOW TIDES

23. Acid Rain in Marine Environment
• reduces ability of marine
organisms to utilize calcium
carbonate
• Coral calcification
rate reduced
15-20%
• Skeletal density
decreased,
branches thinner

24. NUTRIENTS AND ALGAE GROWTH

25. SEDIMENTS

26. BLEACHING

27. SOME LOCAL HUMAN IMPACTS
 thermal effluents
 sewage discharges and agricultural runoff
 mechanical damage to reefs
 sedimentation
 destructive resource extraction practices
 introduced species

28. GLOBAL HUMAN IMPACTS
 Global warming
 UV radiation
 Ocean acidification

29. CORALS AND UV RADIATION
 decreased growth
 decreased rates of calcification
 transplantation experiments (deep corals brought to the
surface) demonstrate corals may be UV-sensitive (exhibit
bleaching and increased mortality)
 coral sperm appears to be UV-sensitive (note spawning
normally takes place at night)

30. POSSIBLE CONSEQUENCES OF STRESSES AND
IMPACTS ON CORALS AND CORAL REEFS
 outright mortality of coral tissues
 breakage of coral colonies
 bleaching
 diseases
 slower growth
 reduced reproduction and recruitment
 competitive exclusion by other organisms
 increased reef erosion

31. MODERN USES OF CORAL REEFS
 Seafood
 Food Additives and Toiletries
 Health and Medicine Products
 Research and Education
 Jewelry and Art
 Marine Aquarium Specimens
 New Land
 Cement & Other Building Supplies
 Shoreline Protection
 Recreation

32. THANK YOU