Coral growth

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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

3. Abiotic factors

4. Latitude High calcification rates are limited to warm waters. Consequently, coral reefs are restricted to tropical seas, generally between 25 N and 25 S latitudes.

5. Temperature Reef building corals cannot tolerate water temperatures of less than18 C (except as in the Florida Keys of the United States), although some corals tolerate temperatures of up to 40 C , optimum growth usually occurs between 23 C and 29 C .

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

13. Biotic factors

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