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Coral growth
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.
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Coral growth
- 1. FACTORS AFFECTING THEGROWTH 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 ratesare limited to warm waters. Consequently, coral reefs are restricted to tropical seas, generally between 250 N and 250 S latitudes.
- 5. Temperature Reef building coralscannot 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, lightis 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.
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- 8. Salinity Hermatypic corals seemto 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 Highturbidity 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 reefsthrive 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 areunable 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 Newreefs 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 relationshipsare especially important in structuring coral-reef communities. between Zooxanthellae, coral polyp Carbondioxide, ammonium phosphate Oxygen, photosynthate
- 15. COMPETITION Competition forlimited 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 majorgroups 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 OFSTRESS ON CORAL REEFS intense storms El Niño disease volcanic eruptions predator population explosions natural stream and river runoff exceptionally low tides
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- 21. STREAM AND RIVERRUNOFF
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- 23. Acid Rain inMarine Environment • reduces ability of marine organisms to utilize calcium carbonate • Coral calcification rate reduced 15-20% • Skeletal density decreased, branches thinner
- 24. NUTRIENTS AND ALGAEGROWTH
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- 27. SOME LOCAL HUMANIMPACTS 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 UVRADIATION 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 OFSTRESSES 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 OFCORAL 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
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