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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

Coral Bleaching 101

Presented by Mark Eakin

Coordinator, NOAA Coral Reef Watch

what is a coral

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

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

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 zooxanthellae6

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

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….

what turns the coral white

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

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

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 warm is warm?

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

can corals recover

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 recover13

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 recover14

Can corals recover?

Corals can begin to recover after a few weeks

Jeff Miller, National Park Service

does bleaching kill corals

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

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 corals17

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

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

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)

hurricanes coral bleaching

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

hurricanes a mixed blessing

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 blessing22

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

can we protect corals from bleaching

Can we protect corals from bleaching?

Shade reefs

Cool reefs

Improve water quality

Reduce other stress

Reduce overfishing

what can you do

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

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