Colorful Corals

Read the passage, and think of the following questions:1.What is coral made up of ?

2.How does coral fulfill their appetite(填饱肚子 )?

3.How does coral multiply themselves(繁衍后代 )?

4.What’s the relationship between coral and sunshine?

Coral Bleaching(珊瑚的死亡 ) 101

Presented by Mark Eakin

Coordinator, NOAA Coral Reef Watch

What is a coral?

- A “coral” is actually a “coral colony”(珊瑚虫聚集地 )

What is a coral?

-Surface is covered by thousands of tiny coral animals, called “polyps”-Polyps are filled with microscopic algae(微小的海藻 )

Anatomy of a coral polyp

-Each polyp looks like a tiny sea anemone (海葵 )

-Ring of stinging tentacles(触角 ) around a central mouth

-Rests in a “cup” on the surface of the colony

What do corals eat?

-Like a sea anemone(海葵 ), the polyp can capture small prey(食物 ) (mostly zooplankton[浮游生物 ]) with its tentacles

What do corals eat?

• Also get nutrition from a symbiotic relationship with zooxanthellae(虫黄藻 )….

What are zooxanthellae?

Algae Fish Shrimp(小虾 )

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

What is coral bleaching?

Coral bleaching is caused by stressPoll question: what might be stressful for a coral? We’ll get back to the answer later….

Healthycoral

Bleached (死亡的 )

coral

What turns the coral white?

- As a stress response, corals expel(驱逐 ) the symbiotic zooxanthellae from their tissues

- The coral tissue is clear, so you see the white limestone skeleton underneath

Healthy coral with algae

Bleached coral with no algae

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 2°C 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?

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?

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

Photo: Caroline Rogers, USGS

Gain weight Get sick Turn orange

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

Photo: Caroline Rogers, USGS

What else can stress do to corals?

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

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?

-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

Can corals recover?

-Corals can begin to recover after a few weeks

Jeff Miller, National Park Service

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://www.publicaffairs.noaa.gov/ 25list.html

http://www.projectaware.org/americas/english/10TYCD.asp

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