92 Scientific American, May 2022
50%
1990 2000 2010 2020
50%
West Indian Ocean
Red Sea, Gulf of Aden Gulf of Oman
South Asia
East Asia
Australia
Caribbean
Brazil
Pacific
Eastern Pacific
0 50% 100%
Colonized by algae
Healthy coral
Colonized by algae
Data notavailableData notavailable Healthy coral
–0.4 0 ̊C +1.2
Sources: “Status of Coral Reefs of the World: 2020,” by ICRI, GCRMN, Australia Institute
of Marine Science and UNEP; NOA A (
sea-surface temperature data
)
GRAPHIC SCIENCE
Text and Graphic by Katie Peek
The United Nations recently released
a sweeping report on the health of the
planet’s coral. Healthy reef cover—where
squishy polyps and colorful algae coat
the white skeletons of hard coral—has
dropped 14 percent in the past decade.
Coastal development, ocean plastic pol-
lution and overfishing all take their toll,
allowing destructive algae to proliferate.
But warming oceans, which bleach
coral, are the biggest threat to reefs world-
wide. The all too familiar story has a few
bright spots, however. Coral rebounded
after major bleaching events in 1998 and
2005, showing recovery is possible. And
the most biodiverse coral in the world—
the so-called Coral Triangle in the west-
ern Pacific Ocean—is holding its ground.
A Checkup on the
World’s Coral Reefs
The prognosis isn’t all bad
Recovery Potential
The warm waters of the
1997–1998 El Niño event
bleached South Asian
coral severely, but a
decade of normal temp
eratures allowed it to
recover. Still, research
ers fear bleaching events
now happen too fre
quently for full recover
ies in between.
A Story of Hope
East Asian reefs have
proved more resilient
than others, possibly
because the region has
long seen more variable
temperatures than other
parts of the ocean. The
region hosts 600 of the
800 known species of
coral and accounts for a
third of the ocean’s reefs.
Color bars show how
warm a region’s water
was each year, relative
to 1971–2000:
Each chart shows the fraction
of coral that is healthy ( pink )
or colonized by
destruc tive algae ( green ),
relative to 1990–2019.
Aqua bars represent
the fraction of
global coral found
in that region:
Key