Coral Reefs in Warming Oceans

• how much of the earth's surface is covered by oceans?

  three quarters
• what are corals?

  colonial animals
• what are corals symbiotic with?

  algae called zooxanthellae
• where are corals found?

  in the tropics
• where is species richness in corals the highest?

  the central indo-pacific
• what is the stress response from corals?

  coral bleaching
• what are corals coloured by?

  algae called zooxanthellae that live within their tissues
• where do corals gain energy from?

  photosynthesis of their symbiotic algae and catching plankton in the water column with their tentacles
• what type of relationship did corals and their symbiotic algae share?

  mutualistic
• why is the relationship between corals and their symbiotic algae mutualistic?

  the algae photosynthesise inside the coral and provide the coral with energy, the coral provides essential nutrients for the algae = this is an adaption to nutrient poor conditions
• give three examples of the essential nutrients that the coral provide for the algae?

  nitrogen, phosphate and sulphur
• when does coral bleaching occur?

  when the relationship between the host and the symbiotic algae is disrupted
• what does coral bleaching result in for the coral?

  loss of tissue biomass and the coral skeleton to be visible through transparent tissue
• what do corals secrete?

  fluorescent proteins that can reflect and dissipate UV light
• when does significant coral bleaching usually occur?

  when degree heating week values reach 4 degrees C weeks
• what does the degree heating weeks value represent?

  the instantaneous bleaching thermal stress during the most recent 12 week period
• what is the degree heating weeks value directly related to?

  the timing and intensity of the coral bleaching
• what are mass bleaching events strongly linked to?

  sustained elevated ocean temperatures
• what is the cellular mechanism behind coral bleaching?

  • damage to the photosynthesis apparatus generates large amounts of reactive oxygen species
  • these overwhelm the oxygen handling pathways
  • causing major cell damage and the host cells to eject the zooxanthellae
• name five of the triggers of coral bleaching?

  heat stress, light stress, hypoxia, hyposalinity and acidification
• what are the five endpoints of coral bleaching?

  cell death of host, digestion of symbiont by host, expulsion of symbiont, host cell detachment and bacterial lysis
• can corals recover from bleaching if the stress is not too prolonged?

  yes
• how do corals recover from bleaching if the stress is not too prolonged?

  symbiotic algae increase in population size and are reabsorbed from the water column
• what happens if corals fail to recover from bleaching?

  mortality
• what does recovery of corals after bleaching require?

  new larvae to settle and establish new colonies on that reef
• when was the global coral bleaching event?

  2014 - 2017
• what % of reefs on the great barrier reef are affected by bleaching?

  93 %
• what is the great coral bleaching event hypothesised to be caused by?

  the strongest El Niño on record
• when was the strongest El Niño event on record hypothesised to cause the great coral bleaching event?

  2014 - 2017
• what was the worst coral bleaching event ever recorded?

  the great coral bleaching event
• what % of coral colonies on the Great Barrier Reef died during the great coral bleaching event?

  67 %
• when does ocean acidification occur?

  when excess carbon dioxide is absorbed from the atmosphere
• what is the pH of sea water?

  slightly alkaline = 8.16
• why are carbonate ions needed in the sea?

  to form shells and skeletons
• what do hydrogen ions do in the sea?

  increase the acidity of the ocean
• what does ocean acidification lead to in terms of ions?

  more hydrogen ions and fewer carbonate ions
• what does having more hydrogen ions due to ocean acidification result in?

  water becomes more acidic
• what does having less calcium ions due to ocean acidification result in?

  having less essential material available for organisms to make structures
• what happens to ocean pH as carbon dioxide increases?

  it decreases, becoming more acidic
• what combine to form calcium carbonate?

  carbonate ions and dissolved calcium