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Coral Bleaching 101


... Eakin. Coordinator, NOAA Coral Reef Watch. What is a coral? ... Ring of stinging tentacles around a central mouth. Rests in a 'cup' on the surface of the colony ... – PowerPoint PPT presentation

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Title: 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

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

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.

What are zooxanthellae?
What are zooxanthellae?
  • Algae that live in the coral polyps surface
  • 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
What is coral bleaching?
Healthy coral
Bleached coral
  • Coral bleaching is caused by stress
  • Poll question what might be stressful for a
    coral? Well get back to the answer later.

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

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

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

Can corals recover?
  • Yes, if the stress doesnt 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
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
Can corals recover?
  • Corals can begin to recover after a few weeks

Jeff Miller, National Park Service
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

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
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
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
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
    reefs limestone structure)

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

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

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

What Can YOU Do?
1. Learn more about coral reefs. 2. Spread the
word. http// 25list.
html http//
Bleaching 101 summary
  • Corals are mineral, animal, AND vegetable
  • Hot water bleaches corals
  • Corals may die after bleaching
  • Diseases follow many warming/bleaching stress