coral bleaching 6-7-06

7/30/2019 Coral Bleaching 6-7-06

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Coral Bleaching 101

Presented by Mark Eakin

Coordinator, NOAA Coral Reef Watch


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What is a coral?

- A coral is actually acoral colony -Rocky limestone

base-Surface is coveredby thousands of tiny

coral animals, calledpolyps -Polyps are filled withmicroscopic algae


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Anatomy of a coral polyp

-Each polyp looks likea tiny sea anemone

-Ring of stingingtentacles around acentral mouth

-Rests in a cup on thesurface of the colony


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What do corals eat?

-Like a sea anemone,the polyp can capture

small prey (mostlyzooplankton) with itstentacles

-Also get nutrition froma symbiotic relationshipwith zooxanthellae.


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What are zooxanthellae?

-Algae that live in thecoral polyps surface layer

-Algae get nutrients and asafe 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


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What is coral bleaching?

Coral bleaching is caused by stressPoll question: what might be stressful for a

coral? Well get back to the answer later.

Healthycoral

Bleachedcoral


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What turns the coral white?

- As a stress response, corals expel thesymbiotic zooxanthellae from their tissues- The coral tissue is clear, so you see the

white limestone skeleton underneath

Healthycoralwithalgae

Bleached

coral withno algae


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What can stress a coral?

-High light or UV levels-Cold temperatures-Low salinity and highturbidity from coastal runoff events or heavy rain-Exposure to air during

very low tides-Major: high water temperatures

Photos: AIMS and GBRMPA


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Thermal stress

-Corals live close to their thermal maximum limit-If water gets 1 or 2 Chigher than the summer average, corals getstressed and bleach

-NOAA satellitesmeasure global oceantemperature and thermal

stress


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How warm is warm?

How hot do you think the ocean has to getbefore corals start to bleach?


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Can corals recover?

-Yes, if the stress doesntlast too long

-Some corals can eat morezooplankton to help survivethe lack of zooxanthellae

-Some species are moreresistant to bleaching, andmore able to recover

Photos: AIMS and GBRMPA


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Can corals recover?

-Corals may eventuallyregain color by repopulatingtheir zooxanthellae-Algae may come from thewater column-Or they may come fromreproduction of the few cellsthat remain in the coral

Jeff Miller, National Park Service


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Can corals recover?

-Corals can begin torecover after a few weeks

Jeff Miller, National Park Service


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Does bleaching kill corals?

-Yes, if the stress is severe-Some of the polyps in a

colony might die-If the bleaching is reallysevere, whole coloniesmight die-Bleaching in Puerto Ricokilled an 800-year-old star coral colony in 2005


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What else can stress do to corals?

Question: what is something that happens topeople when they are highly stressed?

Photo:Caroline Rogers, USGS

Gain weight Get sick Turn orange


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Question: what is something that happens topeople when they are highly stressed?

Photo:Caroline Rogers, USGS

What else can stress do to corals?

Answer: more likely to get sick


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Bleaching and coral disease

-Coral diseases arefound around the world

-High temperaturesand bleaching canleave corals more

vulnerable to disease-Can quickly kill part or all of the coral colony

Marilyn E. Brandt, University of Miami


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Bleaching and bioerosion

-We have seen thatbleaching can kill partor all of a coral colony-Areas of dead coralare more vulnerable tobioerosion (whenanimals wear away thecoral reefs limestonestructure)


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Hurricanes & coral bleaching

The same warm water that causes corals tobleach can also lead to strong hurricanes.

2005:Most named stormsMost hurricanes

Most damage in US


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Hurricanes : a mixed blessing

-Hurricanes can causedirect physical damageto coral reefs

-However, the stormsalso cools the water

-Hurricane Katrina ledto less bleaching in theFlorida Keys, 2005

2 Sept 2005

22 Aug 2005


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Hurricanes: a mixed blessing

Each passing hurricane in 2005 cooled the

water in the Florida Keys.

Dennis9 July

Katrina

26 Aug Rita21 Sept

Wilma24 Oct

Sombrero Reef , FL

S S T ( d e g

C )

DHW ( d e g C w

e ek )


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Can we protect corals from bleaching?

Shade reefs Cool reefs Improve water quality Reduce other stress Reduce overfishing


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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.a


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Bleaching 101: summary

- Corals are mineral, animal, AND vegetable- Hot water bleaches corals- Corals may die after bleaching- Diseases follow many warming/bleachingstress events

coral bleaching 6-7-06

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