Half of the Great Barrier Reef Is Dead

See where coral in the world's largest coral reef system has been bleached to death.

This story appears in the August 2018 issue of National Geographic magazine.

Half of the Great Barrier Reef has been bleached to death since 2016. Mass coral bleaching, a global problem triggered by climate change, occurs when unnaturally hot ocean water destroys a reef’s colorful algae, leaving the coral to starve. The Great Barrier Reef illustrates how extensive the damage can be: Thirty percent of the coral perished in 2016, another 20 percent in 2017. The effect is akin to a forest after a devastating fire. Much of the marine ecosystem along the reef’s north coast has become barren and skeletal with little hope of recovery.

New

Guinea

Great Barrier Reef Marine Park

Australia

Brisbane

Sydney

Canberra

Gulf of

Papua

New

Guinea

Reef bleaching severity

Proportion of individual

reef in 1998, 2002, or

2016 event*

Extreme

(more than 60%)

Cooktown

Moderate (30–60%)

Low (10–29%)

Cairns

Townsville

Australia

Mackay

150 mi

150 km

Worse than expected

Bleaching in 2016 occurred so rapidly that scientists had to retool their predictions for how much heat the reef could endure.

HOW HOT FOR HOW LONG

As climate change warms Earth’s oceans, underwater heat waves last longer. Coral species can’t withstand extended hot periods. They start to die off, which diminishes reef diversity. After heat stress becomes severe, as it did along the northern Great Barrier Reef in 2016, few species remain, and final die-off is rapid.

HEAT STRESS

Great Barrier Reef Far Northern

Management Area

16

12

8

4

Heat stress in 2016 killed 80% of coral in this section of the reef.

2014

2015

2016

2017

Degree heating week (DHW)

combines intensity and duration of heat stress into a single number.

NO TIME FOR RECOVERY

Severe regional bleaching used to hit a given reef about every 27 years. Since the 1980s, the pace has accelerated­ to every six. Even in the best conditions, badly damaged reefs take at least 10 years to rebound. The Great Barrier Reef, struck two years in a row, may never fully recover.

A healthy partnership

Algae feed the coral; coral provides shelter and nutrients to the algae.

Enlarged

below

Relationship breakdown

Coral stressed from overly hot water expels the algae, causing the coral to starve. The skeleton of dying coral decays once exposed.

Stressed

Healthy

Bleached

Zooxanthellae algae

Decay

*MOST SEVERE SCORE (SOME REEFS SURVEYED IN MORE

THAN ONE BLEACHING).

 

LAUREN E. JAMES AND CLARE TRAINOR, NGM STAFF

ART: MATTHEW TWOMBLY. SOURCES: ARC CENTRE OF

EXCELLENCE FOR CORAL REEF STUDIES; NOAA CORAL

REEF WATCH; ROBIN BEAMAN, JAMES COOK UNIVERSI-

TY; AUSTRALIAN HYDROGRAPHIC OFFICE; GEOSCIENCE

AUSTRALIA; AUSTRALIAN INSTITUTE OF MARINE

SCIENCE; RAY BERKELMANS AND OTHERS, CORAL REEFS

23, 2004; © OPENSTREETMAP CONTRIBUTORS,

AVAILABLE UNDER OPEN DATABASE LICENSE:

OPENSTREETMAP.ORG/COPYRIGHT

Half of the Great Barrier Reef has been bleached to death since 2016. Mass coral bleaching, a global problem triggered by climate change, occurs when unnaturally hot ocean water destroys a reef’s colorful algae, leaving the coral to starve. The Great Barrier Reef illustrates how extensive the damage can be: Thirty percent of the coral perished in 2016, another 20 percent in 2017. The effect is akin to a forest after a devastating fire. Much of the marine ecosystem along the reef’s north coast has become barren and skeletal with little hope of recovery.

New

Guinea

Direction of view

HEAT STRESS

HOW HOT FOR HOW LONG

As climate change warms Earth’s oceans, underwater heat waves last longer. Coral species can’t withstand extended hot periods. They start to die off, which diminishes reef diversity. After heat stress becomes severe, as it did along the northern Great Barrier Reef in 2016, few species remain, and final die-off is rapid.

Great Barrier Reef Far Northern Management Area

Degree heating week (DHW)

combines intensity and duration of heat stress into a single number.

16

12

8

4

Great Barrier Reef Marine Park

Heat stress in 2016 killed 80% of coral in this section of the reef.

Australia

Brisbane

Sydney

2014

2015

2016

2017

Canberra

Mackay

Reef bleaching severity

Proportion of individual reef

in 1998, 2002, or 2016 event*

Extreme (more than 60%)

Moderate (30–60%)

Low (10–29%)

Townsville

New

Guinea

Cairns

Cooktown

Australia

Gulf of

Papua

Far Northern

Management Area

Worse than expected

Bleaching in 2016 occurred so rapidly that scientists had to retool their predictions for how much heat the reef could endure.

Lockhart

River

Cape York

Peninsula

N

Saibai

Island

New

Guinea

Stressed

Healthy

Bleached

Enlarged

at right

NO TIME FOR RECOVERY

Severe regional bleaching used to hit a given reef about every 27 years. Since the 1980s, the pace has accelerated­ to every six. Even in the best conditions, badly damaged reefs take at least 10 years to rebound. The Great Barrier Reef, struck two years in a row, may never fully recover.

Zooxanthellae algae

Decay

A healthy partnership

Algae feed the coral; coral provides shelter and nutrients to the algae.

Relationship breakdown

Coral stressed from overly hot water expels the algae, causing the coral to starve. The skeleton of dying coral decays once exposed.

SCALE VARIES IN THIS PERSPECTIVE. DISTANCE FROM SAIBAI ISLAND TO CAPE YORK IS 90 MILES. *MOST SEVERE SCORE (SOME REEFS SURVEYED IN MORE THAN ONE BLEACHING). LAUREN E. JAMES AND CLARE TRAINOR, NGM STAFF. TERRAIN RENDERING: CHARLES PREPPERNAU. ART: MATTHEW TWOMBLY. SOURCES: ARC CENTRE OF EXCELLENCE FOR CORAL REEF STUDIES; NOAA CORAL REEF WATCH; ROBIN BEAMAN, JAMES COOK UNIVERSITY; AUSTRALIAN HYDROGRAPHIC OFFICE; GEOSCIENCE AUSTRALIA; AUSTRALIAN INSTITUTE OF MARINE SCIENCE; RAY BERKELMANS AND OTHERS, CORAL REEFS 23, 2004; © OPENSTREETMAP CONTRIBUTORS, AVAILABLE UNDER OPEN DATABASE LICENSE: OPENSTREETMAP.ORG/COPYRIGHT