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Coral Bleaching 101

Coral Bleaching 101. Presented by Mark Eakin Coordinator, NOAA Coral Reef Watch. What is a coral?. A “coral” is actually a “coral colony” Rocky limestone base Surface is covered by thousands of tiny coral animals, called “polyps” Polyps are filled with microscopic algae.

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Coral Bleaching 101

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  1. Coral Bleaching 101 Presented by Mark Eakin Coordinator, NOAA Coral Reef Watch

  2. What is a coral? A “coral” is actually a “coral colony” Rocky limestone base Surface is covered by thousands of tiny coral animals, called “polyps” Polyps are filled with microscopic algae

  3. Anatomy of a coral polyp Each polyp looks like a tiny sea anemone Ring of stinging tentacles around a central mouth Rests in a “cup” on the surface of the colony

  4. What do corals eat? Like a sea anemone, the polyp can capture small prey (mostly zooplankton) with its tentacles Also get nutrition from a symbiotic relationship with zooxanthellae….

  5. What are zooxanthellae? Shrimp Algae Fish

  6. What are zooxanthellae? Algae that live in the coral polyp’s surface layer Algae get nutrients and a safe place to grow Corals get oxygen and help with waste removal Corals also get most of their food from the algae Photo: Michael ten Lohuis

  7. What is coral bleaching? Healthy coral Bleached coral Coral bleaching is caused by stress Poll question: what might be stressful for a coral? We’ll get back to the answer later….

  8. What turns the coral white? Healthy coral with algae Bleached coral with no algae - As a stress response, corals expel the symbiotic zooxanthellae from their tissues - The coral tissue is clear, so you see the white limestone skeleton underneath

  9. What can stress a coral? High light or UV levels Cold temperatures Low salinity and high turbidity from coastal runoff events or heavy rain Exposure to air during very low tides Major: high water temperatures Photos: AIMS and GBRMPA

  10. Thermal stress Corals live close to their thermal maximum limit If water gets 1 or 2°C higher than the summer average, corals get stressed and bleach NOAA satellites measure global ocean temperature and thermal stress

  11. How warm is warm? How hot do you think the ocean has to get before corals start to bleach?

  12. Can corals recover? Yes, if the stress doesn’t last too long Some corals can eat more zooplankton to help survive the lack of zooxanthellae Some species are more resistant to bleaching, and more able to recover Photos: AIMS and GBRMPA

  13. Can corals recover? Corals may eventually regain color by repopulating their zooxanthellae Algae may come from the water column Or they may come from reproduction of the few cells that remain in the coral Jeff Miller, National Park Service

  14. Can corals recover? Corals can begin to recover after a few weeks Jeff Miller, National Park Service

  15. Does bleaching kill corals? Yes, if the stress is severe Some of the polyps in a colony might die If the bleaching is really severe, whole colonies might die Bleaching in Puerto Rico killed an 800-year-old star coral colony in 2005

  16. What else can stress do to corals? Photo: Caroline Rogers, USGS Question: what is something that happens to people when they are highly stressed? Gain weight Get sick Turn orange

  17. What else can stress do to corals? Photo: Caroline Rogers, USGS Question: what is something that happens to people when they are highly stressed? Answer: more likely to get sick

  18. Bleaching and coral disease Coral diseases are found around the world High temperatures and bleaching can leave corals more vulnerable to disease Can quickly kill part or all of the coral colony Marilyn E. Brandt, University of Miami

  19. Bleaching and bioerosion We have seen that bleaching can kill part or all of a coral colony Areas of dead coral are more vulnerable to bioerosion (when animals wear away the coral reef’s limestone structure)

  20. Hurricanes & coral bleaching The same warm water that causes corals to bleach can also lead to strong hurricanes. 2005: Most named storms Most hurricanes Most damage in US

  21. Hurricanes : a mixed blessing • Hurricanes can cause direct physical damage to coral reefs • However, the storms also cools the water • Hurricane Katrina led to less bleaching in the Florida Keys, 2005 22 Aug 2005 2 Sept 2005

  22. Sombrero Reef , FL Hurricanes: a mixed blessing DHW (degC week) SST (degC) Each passing hurricane in 2005 cooled the water in the Florida Keys. Dennis 9 July Katrina 26 Aug Rita 21 Sept Wilma 24 Oct

  23. Can we protect corals from bleaching? Shade reefs Cool reefs Improve water quality Reduce other stress Reduce overfishing

  24. What Can YOU Do? • 1. Learn more about coral reefs. • 2. Spread the word. • http://www.publicaffairs.noaa.gov/ 25list.html • http://www.projectaware.org/americas/english/10TYCD.asp

  25. Bleaching 101: summary Corals are mineral, animal, AND vegetable Hot water bleaches corals Corals may die after bleaching Diseases follow many warming/bleaching stress events

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