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SCIENCE
 

Climate change is a major threat to coral living on the Great Barrier Reef

This photo taken on September 22, 2014, shows a turtle resting on coral on the Great Barrier Reef – an international marine icon and vast underwater kingdom boasting some of the rarest animals and plants in the world. Photo by: WILLIAM WEST/AFP/Getty Images
This photo taken on September 22, 2014, shows a turtle resting on coral on the Great Barrier Reef – an international marine icon and vast underwater kingdom boasting some of the rarest animals and plants in the world. Photo by: WILLIAM WEST/AFP/Getty Images

The Great Barrier Reef is famous for its kaleidoscope of colors: a rainbow of sea creatures swimming past bright corals.

Last year, however, something strange happened — the reef's coral turned bone-white. Scientists call this "bleaching." 

Unfortunately, the coral may never return to its previous color, a new study says. Scientists say that rising temperatures are to blame, and that swift action is needed to save the Great Barrier Reef.

Heat Stress Turns Coral White

Record-high temperatures in 2015 and 2016 caused the bleaching event. A bleached-white coral means that it has been stressed by the heat. This stress causes the reef to expel the algae that lives in its tissue. However, the algae also provides the reef with food. Losing algae means the reef loses energy.

Bleached coral is more likely to become diseased. Without sufficient time to recover — which can take one decade or more depending on the type of coral — it can die.

For the new study released late Wednesday, an Australian-led team examined the impact of three major bleaching events: in 1998, 2002 and 2016. The bleaching happened all along the reef, which stretches for 1,400 miles.

They found that in 2016, more than four times as much coral faced extreme bleaching than the two previous events. 

Only 9 percent escaped bleaching altogether, compared with more than 40 percent in 2002 and 1998.

The Damage Is Likely To Be Permanent

The team said that the chances of the northern Great Barrier Reef returning to its pre-bleached days are very slim. The scale of damage that occurred in 2016 was just too much, they said. Scientists also warned that it is highly likely that a fourth bleaching will happen in the next 10 or 20 years, as global temperatures continue to rise.

Earlier this month, researchers warned that the reef was already experiencing a second straight year of bleaching.

Local wildlife experts have tried to protect the reefs. But they cannot properly protect it from the extreme heat, the researchers wrote in the journal Nature. That is part of a global problem. 

Still, scientists and conservationists are focusing on new plans to protect the reef. They are trying to maintain the quality of the water around it. But even the most highly protected reefs cannot escape the dangers of heat stress, they said.

Conservation Efforts Are Failing

Helping the coral recover will become more challenging and less effective in coming decades, the study said. 

Local work to conserve and protect the site has had "no discernible effect" on helping corals resist the heat, they say.

Terry Hughes, part of Australia's Centre of Excellence for Coral Reef Studies, helped lead the reef study. At the same time the study was released, Hughes unveiled plans to track the reef's bleaching this year. Hughes said researchers were heading out again to survey the coral from both the sky and underwater.

"We’re hoping that the next two to three weeks will cool off quickly, and this year’s bleaching won’t be anything like last year," he said. "The severity of the 2016 bleaching was off the chart." Australia's summer is ending. Its seasons are the opposite of the U.S. since it is located in the Southern Hemisphere.

Highest-Ever Sea Temperatures Recorded Last Year

Janice Lough, from the Australian Institute of Marine Science, helped lead the study. She said the average sea-surface temperatures for the Australian summer in 2016 were the highest ever recorded in the Great Barrier Reef.

"In each of the three events since 1998, the pattern of bleaching matches exactly where the warmest water was each year. That allows us to predict when and where bleaching is likely to occur this year,” she added.

Hughes and Lough agree climate change is the number-one threat to the reef. They argue that the only solution was "urgent and rapid action" to limit global warming, which will only increase water temperatures and cause more coral to die.

Dying Coral Will Only Get Worse With Time

"It broke my heart to see so many corals dying on northern reefs on the Great Barrier Reef in 2016,” said Hughes. He led surveys of the reef from aircraft, which revealed the damage.

"With rising temperatures due to global warming, it’s only a matter of time before we see more of these events. A fourth event after only one year is a major blow to the reef," Hughes said.

The world's nations met in Paris in 2015 to discuss global warming. They agreed to limit burning of fossil fuels. The countries hope this will limit the average warming of Earth to 2 degrees Celsius, or 3.6 degrees Fahrenheit. Still, as this latest bleaching event shows, that may not be enough to save the corals.

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1
Anchor 2: Central Idea

Which two of the following sentences from the article include CENTRAL ideas of the article?

  1. Unfortunately, the coral may never return to its previous color, a new study says.

  2. Scientists say that rising temperatures are to blame, and that swift action is needed to save the Great Barrier Reef.

  3. They found that in 2016, more than four times as much coral faced extreme bleaching than the two previous events.

  4. "It broke my heart to see so many corals dying on northern reefs on the Great Barrier Reef in 2016,” said Hughes.

A

1 and 3

B

2 and 4

C

2 and 3

D

3 and 4

2
Anchor 2: Central Idea

Which statement would be MOST important to include in a summary of the article?

A

Since the Great Barrier Reef stretches for 1,400 miles along the Australian coast, future signs of bleaching will be monitored closely.

B

Because there is a pattern of bleaching that scientists have documented, additional damage to the reef can be expected.

C

Even if efforts to curb climate change are successful, it may be too late to save the Great Barrier Reef.

D

Although bleaching of the reef is caused by climate change, local work is focused on conservation of the site.

3
Anchor 4: Word Meaning & Choice

Read the paragraph from the introduction [paragraphs 1-3].

The Great Barrier Reef is famous for its kaleidoscope of colors: a rainbow of sea creatures swimming past bright corals.

How does using the word "kaleidoscope" affect the tone of this sentence?

A

It conveys the sense that the reef is a fragile structure.

B

It conveys a shifting, jewel-like atmosphere.

C

It conveys a sense of subdued movement.

D

It conveys the geometric quality of the reef.

4
Anchor 4: Word Meaning & Choice

Read the paragraph from the section "Heat Stress Turns Coral White."

Bleached coral is more likely to become diseased. Without sufficient time to recover — which can take one decade or more depending on the type of coral — it can die.

Which answer choice is the BEST definition of the word "sufficient" as used in the sentence?

A

adequate

B

generous

C

average

D

sparse

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