Threats

• Physical damage-

  • hard objects can kill polyps as they are pushed against the hard limestone beneath the living cells
  • litter such as bottles, lost fishing gear, boat anchors and careless divers can all damage reefs
  • damage is also caused by extraction of coral for land reclamation and construction
• Collection of ornaments and souvenirs-

  • many species from coral reefs are collected to be sold as ornaments such as mollusc shells and hard corals
  • trade in about 2000 species of coral is restricted by CITES Appendix 2
• Sedimentation-

  turbid water carried by rivers or sediments disturbed by coastal developments can cover and kill corals
• Pollution-

  • a wide range of pollutants can harm coral reefs, large oil spills can cover coral reefs
  • even at lower concentrations oil is toxic to corals, nutrients such as nitrates and phosphates from agricultural run off and sewage effluents can stimulate the growth ofthe symbiotic algae within the polyps and prevents the release of eggs when the corals reproduce
  • ocean acidification caused by increased carbon dioxide concentrations in the atmosphere
  • more carbon dioxide dissolves in the oceans producing the carbonic acid which makes the oceans more acidic, difficult produce polyp skeleton
• Coral bleaching -

  • this occurs when the symbiotic algae within the coral polyps are expelled, bleached corals look pale
  • this can be caused by a variety of natural and anthropogenic factors
  • one natural factor is the raised light levels caused by increased solar activity
  • human causes are increased water temperatures caused by global climate change
  • low oxygen levels due to high zooplankton activity caused by over fishing of their fish predators
  • pollution including sewage and sunscreen products
  • bleached coral polyps which are not dead and may regain algae in the future grow very slowly
• Introduced species -

  • non-indigenous species introduced in many ways like:
  • from ballast water discharged from ships
  • escaped fish and crustaceans from fish farms
  • accidental and intentional releases from aquaria

  The Red Lionfish was accidentally introduced to the Caribbean in the 1990's and have few predators so spread rapidly and have reduced the populations of indigenous fish species
• Fishing -

  • this is not always damaging but if the catch rate is excessive then over fishing can reduce fish populations and affect other inter-dependant species
• Coastal developments -

  • the expansion of coastal towns , the construction of tourist resorts, ports and marinas can destroy coral reefs directly and increase turbidity causing damage to reefs near the dvelopments
• Loss of associated habitats -

  • mangroves and seagrass beds help to trap suspended sediments and reduce water turbidity
  • they also provide nursery grounds for many of the fish species hat live as adults on coral reefs
  • if the mangroves and seagrass beds are damaged then the coral reefs nearby become damaged too