Scientific American - USA (2022-05)

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