Lecture 14: Coral Reefs and Climate Change

• Biogenic


  Made from living things
• Coral


  • Animals that make a skeleton of calcium carbonate
  • Individual coral is called a colony
  • Colony is made up of multiple identical polyps
• Polyp


  Individual genetically identical organism that makes up a coral colony
• Corals are related to anemones
• Symbiosis


  Two different organisms living together and relying on each other
• Zooxanthellae


  Tiny photosynthetic algae that live within coral tissues
• Coral reef formation

  1. Corals grow and accumulate broken coral fragments

  2. Coral fragments harden and consolidate over time

  3. Corals continue growing upwards creating a reef structure
• Types of coral reefs

  • Fringing reef
  • Barrier reef
  • Atoll
• Coral reefs only occur in the tropics
• The Pacific Ocean has the highest coral diversity
• Threats to coral reefs

  • Warming
  • Acidification
  • Pollution
  • Sedimentation
  • Overfishing
• Coral bleaching


  Corals expel their zooxanthellae in response to stress, usually when temperature increases
• Healthy coral


  • Expels zooxanthellae when stressed
  • Zooxanthellae return when stress is relieved
  • Coral recovers
• Continued warming after bleaching

  Coral dies with seaweed growing on it
• Corals can only survive for so long without their zooxanthellae
• Bleaching


  A break in the stress of bleaching
• Coral bleaching cycle


  1. Healthy coral

  2. Coral bleaches

  3. Coral recovers

  4. Coral becomes healthy again
• Zooxanthellae


  Photosynthesizing organisms that provide food for corals
• Corals can only survive so long without their zooxanthellae
• Warm waters


  Break the cycle of coral recovery
• Oceans are warming, leading to more frequent and longer duration heat waves
• Tropical species like corals have a very narrow range of ideal temperatures
• Even small temperature changes can cause corals to bleach
• Widespread and frequent coral bleaching events have been observed from 2014-2016
• Ocean acidification makes it harder for corals to build skeletons and slows their early growth and development
• Weaker coral skeletons


  Break more easily, harder for corals to maintain and rebuild reefs
• With slower coral development, corals are vulnerable to predation for longer, and take longer to reach reproductive age
• Coral skeleton density is projected to decrease by 14-20% due to ocean acidification
• Assisted evolution


  Growing corals in the lab, selecting for heat-resistant traits, and breeding them to create "super babies" that can survive warming
• Many of the plants and animals we use today have been significantly altered through selective breeding