Coral Reefs - Part 3 Threats

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  • Threats to coral reefs
    • Physical damage
      • Swimmers, divers, boat anchors and litter
    • Pollution
      • Oils, pesticides and cyanide used illegally by some fishermen kill polyps
      • Fertiliser run-off from farms causes eutrophication
    • Souvenirs and ornaments
      • 2000 species of coral are protected by CITES Appendix II but coral is still collected to sell as tourist souvenirs    
    • Fishing
      • Overexploitation harms food webs
      • Dynamite and cyanide used in fishing kills polyps
    • Sediments
      • Rivers carry sediments from eroding farmland, land reclamation projects and coastal developments to the sea. If it settles, it kills the polyps. 
    • Climate change
      • If temperatures keep rising the polyps will expel their symbiotic algae, causing the reef to ‘bleach’.  This results in poor food chains and are more sensitive to other damage.
      • Sea-level rise mean that the symbiotic algae will not be close enough to the surface to photosynthesise    
      • A higher level of CO2 increases the water acidity which may dissolve the limestone that forms the reef    
    • Crown of Thorns Starfish
      • A natural predator of the polyps, that's population is growing due to overfishing of it's predators
    • Disease and predation
      • Algae that grow on the surface of polyps (not the symbiotic algae!) provide sugars to bacteria that kill polyps    

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