A healthy part of the Great Barrier Reef (left) and a bleached part of the Great Barrier Reef (right)

GARY BELL/OCEANWIDEIMAGES.COM (HEALTHY REEF); XL CATLIN SEAVIEW SURVEY (BLEACHED REEF)

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TEKS: Science: 3.2A, 4.2A, 5.2A, 6.2A, 3.4B, 4.4B, 5.4B, 6.4B; ELA: 3.13, 4.11, 5.11, 6.10

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In Hot Water

Can super-corals save a warming reef?

November 2016
By Amy Barth

JIM MCMAHON/MAPMAN®

Not far off the coast of eastern Australia lies the largest living structure in the world: the Great Barrier Reef. This colorful underwater habitat stretches 2,000 kilometers (1,200 miles) from end to end.

The reef is made of millions of individual corals. Corals look like plants, but they’re actually tiny animals that live in clusters. Their hard skeletons form reefs, which provide food and shelter for ocean animals (see How Corals Build Reefs). Normally, the Great Barrier Reef is teeming with fish, crabs, turtles, and other animals.

Recently, though, the world’s biggest reef has come under threat. It’s suffering from the largest-ever coral bleaching event, when corals get sick and turn white. Many of the corals won’t survive. Other reefs around the world—and the animals that live in them—are also in danger.

Marine biologist Ruth Gates has a plan to help save reefs. In an island lab at the University of Hawaii, she and her team are breeding corals that can survive bleaching. They hope that planting these super-corals in sick reefs could help the reefs recover.

The Great Barrier Reef is the world’s largest living structure. It’s found in the ocean near eastern Australia. The colorful reef stretches 2,000 kilometers (1,200 miles) from end to end. 

The reef is made up of millions of living things called corals. Corals look like plants. But they’re actually tiny animals! They live in clusters. Their hard skeletons form reefs (see How Corals Build Reefs). Ocean animals use the reefs for food and shelter. The Great Barrier Reef is usually full of fish, crabs, turtles, and other animals.

But the Great Barrier Reef is in trouble. It recently suffered from coral bleaching. That’s when corals get sick and turn white. This time, more corals got sick than ever before. 

Many of the corals won’t survive. Other reefs around the world are also in danger. That means the animals that live in them are in danger too.

Ruth Gates is an ocean biologist. She has a plan to help save reefs. She works in a lab at the University of Hawaii. Her team there raises special corals. These corals can survive bleaching. Gates hopes she can plant these super-corals in sick reefs in the future. That could help the reefs recover.

A Heated Problem

Bleaching happens when the water corals live in gets warmer than usual. Ocean temperatures have risen in recent years because of global climate change. And this year, El Niño (el NEEN-yoh)—a warm climate pattern in the Pacific Ocean—made things worse. 

Warm water hurts coral’s relationship with tiny plant-like organisms called algae (AL-jee). The algae live inside corals and give them their color. Usually, the two species cooperate. The corals protect the algae. In exchange, the algae turn energy from sunlight into food for the corals.  

Corals live underwater. When that water gets warmer, corals can bleach. Ocean temperatures have been rising in recent years. That’s mainly because global climate change is warming Earth. This year, a warm weather pattern called El Niño (el NEEN-yoh) hit the Pacific Ocean. That made things worse. 

Why does warm water hurt corals? Corals have important partners. They live with tiny plant-like life called algae (AL-jee). The algae live inside corals. They give the corals their color. 

Usually, corals and algae work together. The corals protect the algae. In return, the algae feed the corals. They turn sunlight into food.

How Corals Build Reefs

A coral reef is made of millions of tiny animals. They grow and reproduce to build up the reef.

KATE FRANCIS

How Corals Build Reefs

A coral reef is made of millions of tiny animals. They grow and reproduce to build up the reef.

KATE FRANCIS

But when temperatures rise, the algae can’t function. “That makes the corals want to get rid of them,” says Gates. Once corals expel the colorful algae, the corals’ pale skeletons show through their clear bodies. They appear white, or “bleached.”

When corals bleach, the entire reef ecosystem suffers. Without algae, corals don’t get enough food. They stop growing and may die and break apart. They can no longer help all the animals that rely on them. 

But when it’s too warm, algae can’t make food. “That makes the corals want to get rid of them,” says Gates. The corals kick out the colorful algae. Without them, the coral’s white skeletons show. That’s why scientists call it “bleaching.” 

Bleaching harms the whole reef ecosystem. Without algae, corals don’t get enough food. They stop growing. They may die and break apart. They can’t help all the animals that live in them anymore. 

CALEB JONES/AP PHOTO

At her lab, marine biologist Ruth Gates grows corals that can resist bleaching.

Reef Report

Rising ocean temperatures have put more than 93 percent of the Great Barrier Reef at risk of bleaching. Other corals around the world are in trouble too. Reefs around Florida and near Gates’s lab in Hawaii have all bleached this year.

Warmer water isn’t the only problem coral reefs face. Pollution has also made oceans more acidic. That can cause corals’ skeletons to dissolve. With one-fourth of all ocean animals making their home in coral reefs, that leaves a lot of underwater life at risk.

But Gates believes corals can make a comeback. To help, she’s growing superstrong corals in her lab near Honolulu. 

When corals bleach nearby, Gates and her team dive into the reef and look for corals that survived. If they find any, they break off samples. “If you go out during a bleaching event, many corals are white,” says Gates. “But there’s always an individual that looks healthy.”

The ocean around the Great Barrier Reef is warming up. More than 93 percent of the reef is now at risk of bleaching. Other corals around the world are in trouble too. Reefs around Florida have bleached this year. So have reefs in Hawaii, near Gates’s lab.

Warmer water isn’t the only problem coral reefs face. Pollution is making oceans more acidic. That means the water can eat away at corals’ skeletons. One-fourth of all ocean animals live in coral reefs. Now many of them are in danger. 

Gates thinks corals can be saved. She’s trying to help. Her lab grows superstrong corals. 

Gates is a diver. Her team swims to nearby reefs after corals bleach. They look for corals that survived. They collect any they find. “If you go out during a bleaching event, many corals are white,” says Gates. “But there’s always an individual that looks healthy.”

HUGH GENTRY VIA VULCAN, INC. (DIVER); CALEB JONES/AP PHOTO (JUVENILE CORAL)

Super-Corals

Back at her lab, Gates puts the healthy coral samples in tanks. She bathes some of them in warm water. This imitates the conditions that cause coral bleaching in the wild. 

Gates is most excited about the corals that survive this treatment. She selects these corals and breeds them, creating baby corals that can resist bleaching too. Then she plants the baby corals on an ocean reef near her lab, where she can watch them grow. 

Over time, Gates plans to breed stronger and stronger corals in her lab. She hopes that this will one day help corals overcome the threats they face. “Someday,” she says, “we can put these super-corals in the ocean to help reefs survive.” 

Gates puts the healthy corals in tanks. She bathes some of them in warm water. She wants to copy what makes corals bleach in the wild. 

Some corals survive the treatment. That makes Gates excited. She grows more of these corals. They don’t bleach either. Then she plants the new corals on a nearby reef. She watches them grow. 

Over time, Gates plans to grow even stronger corals. She hopes to use them to help save reefs. “Someday,” she says, “we can put these super-corals in the ocean to help reefs survive.” 

Acidic Ocean

How does acidic water affect reefs?

Step 8

Observe

Pollution makes oceans more acidic. That harms corals. Coral skeletons are made of the substance calcium carbonate. To mimic coral, you can use seashells, which are made of the same substance.

Pollution makes oceans more acidic. That harms corals. Coral skeletons are made of the substance calcium carbonate. To mimic coral, you can use seashells, which are made of the same substance.

Ask a Research Question

How does acidic ocean water affect calcium carbonate?

How does acidic ocean water affect calcium carbonate?

Form a Hypothesis Based on This Question:

What will happen to seashells in increasingly acidic liquids? 

What will happen to seashells in increasingly acidic liquids? 

Materials

• safety goggles
• 3 jars
• masking tape
• marker
• measuring cup
• white vinegar
• spoon
• 3 seashells (available at craft stores)
• balance
• paper towels
• pencil and paper

• safety goggles
• 3 jars
• masking tape
• marker
• measuring cup
• white vinegar
• spoon
• 3 seashells (available at craft stores)
• balance
• paper towels
• pencil and paper

Procedure

1. Put on safety goggles. Use the masking tape and marker to label the jars A, B, and C. 

2. Now make mixtures with different levels of acidity. Use the measuring cup to add 1 cup of water to Jar A. This liquid is the least acidic.

3. Add 1/2 cup of water and 1/2 cup of vinegar to Jar B. Vinegar makes the mixture more acidic. Stir with the spoon.

4. Add 1 cup of vinegar to Jar C.

5. Use the balance to find the mass of each seashell. Record these measurements.

6. Place one shell in each jar, keeping track of which shell goes in which jar. Record any changes you see in the liquid. 

7. After 24 hours, use the spoon to remove the shells. Dry them off with a paper towel.

8. Use the balance to record the new mass of each shell. Note any changes you observe in its shape, size, and texture.

1. Put on safety goggles. Use the masking tape and marker to label the jars A, B, and C. 

2. Now make mixtures with different levels of acidity. Use the measuring cup to add 1 cup of water to Jar A. This liquid is the least acidic.

3. Add 1/2 cup of water and 1/2 cup of vinegar to Jar B. Vinegar makes the mixture more acidic. Stir with the spoon.

4. Add 1 cup of vinegar to Jar C.

5. Use the balance to find the mass of each seashell. Record these measurements.

6. Place one shell in each jar, keeping track of which shell goes in which jar. Record any changes you see in the liquid. 

7. After 24 hours, use the spoon to remove the shells. Dry them off with a paper towel.

8. Use the balance to record the new mass of each shell. Note any changes you observe in its shape, size, and texture.

Results

How did the mass of each shell change? Subtract each shell’s final mass from its starting mass to find out. Display your results in a table.

How did the mass of each shell change? Subtract each shell’s final mass from its starting mass to find out. Display your results in a table.

Conclusions

1. How did each mixture change the shells?

2. Based on your results, how would you expect acidic ocean water to affect coral reefs?

1. How did each mixture change the shells?

2. Based on your results, how would you expect acidic ocean water to affect coral reefs?

Acidic Ocean

How does acidic water affect reefs?

Step 8

Observe

Pollution makes oceans more acidic. That harms corals. Coral skeletons are made of the substance calcium carbonate. To mimic coral, you can use seashells, which are made of the same substance.

Pollution makes oceans more acidic. That harms corals. Coral skeletons are made of the substance calcium carbonate. To mimic coral, you can use seashells, which are made of the same substance.

Ask a Research Question

How does acidic ocean water affect calcium carbonate?

How does acidic ocean water affect calcium carbonate?

Form a Hypothesis Based on This Question:

What will happen to seashells in increasingly acidic liquids? 

What will happen to seashells in increasingly acidic liquids? 

Materials

• safety goggles
• 3 jars
• masking tape
• marker
• measuring cup
• white vinegar
• spoon
• 3 seashells (available at craft stores)
• balance
• paper towels
• pencil and paper

• safety goggles
• 3 jars
• masking tape
• marker
• measuring cup
• white vinegar
• spoon
• 3 seashells (available at craft stores)
• balance
• paper towels
• pencil and paper

Procedure

1. Put on safety goggles. Use the masking tape and marker to label the jars A, B, and C. 

2. Now make mixtures with different levels of acidity. Use the measuring cup to add 1 cup of water to Jar A. This liquid is the least acidic.

3. Add 1/2 cup of water and 1/2 cup of vinegar to Jar B. Vinegar makes the mixture more acidic. Stir with the spoon.

4. Add 1 cup of vinegar to Jar C.

5. Use the balance to find the mass of each seashell. Record these measurements.

6. Place one shell in each jar, keeping track of which shell goes in which jar. Record any changes you see in the liquid. 

7. After 24 hours, use the spoon to remove the shells. Dry them off with a paper towel.

8. Use the balance to record the new mass of each shell. Note any changes you observe in its shape, size, and texture.

1. Put on safety goggles. Use the masking tape and marker to label the jars A, B, and C. 

2. Now make mixtures with different levels of acidity. Use the measuring cup to add 1 cup of water to Jar A. This liquid is the least acidic.

3. Add 1/2 cup of water and 1/2 cup of vinegar to Jar B. Vinegar makes the mixture more acidic. Stir with the spoon.

4. Add 1 cup of vinegar to Jar C.

5. Use the balance to find the mass of each seashell. Record these measurements.

6. Place one shell in each jar, keeping track of which shell goes in which jar. Record any changes you see in the liquid. 

7. After 24 hours, use the spoon to remove the shells. Dry them off with a paper towel.

8. Use the balance to record the new mass of each shell. Note any changes you observe in its shape, size, and texture.

Results

How did the mass of each shell change? Subtract each shell’s final mass from its starting mass to find out. Display your results in a table.

How did the mass of each shell change? Subtract each shell’s final mass from its starting mass to find out. Display your results in a table.

Conclusions

1. How did each mixture change the shells?

2. Based on your results, how would you expect acidic ocean water to affect coral reefs?

1. How did each mixture change the shells?

2. Based on your results, how would you expect acidic ocean water to affect coral reefs?

Earth Science
Earth's Waters
El Niño

a warm climate pattern that affects the Pacific Ocean every few years
acidic

able to eat away at other substances    
climate change

a change in Earth’s average temperature and weather patterns caused by human activity
coral bleaching

a sickness that affects coral reefs
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