April 4, 2022 - Heatwave Impacts Great Barrier Reef

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Great Barrier Reef
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When viewed from space, Australia’s Great Barrier Reef appears to be a
string of precious gems strung across the Coral Sea just off the
Queensland coast. When viewed from Earth, the uniqueness of this
precious ecosystem becomes even more obvious. According to the United
Nations Education, Science and Cultural Organization (UNESCO) World
Heritage Convention, the Great Barrier Reef is a site of remarkable
variety and beauty. It contains the world’s largest collection of coral
reefs, with 400 types of coral, 1,500 species of fish, and 4,000 types
of mollusk. It also holds great scientific interest as the habitat of
species such as the dugong (‘sea cow’) and the large green turtle,
which are threatened with extinction. Because the diversity of species
and habitats—and their unique interconnectivity—make the Great Barrier
Reef one of the richest and most complex natural ecosystems on Earth,
this natural wonder was inscribed on the World Heritage List in October
1981.

Despite the fact that no other World Heritage property contains such
biodiversity, the Great Barrier Reef is in trouble. In early March
2022, sea temperatures across the reef spiked, creating heatwave
conditions. On April 1, the Australian Government’s Great Barrier Reef
Marine Park Authority confirmed that these warm temperatures had
created a mass bleaching event of the reef, with bleaching observed at
multiple reefs in all four management areas of the Reef. This was
considered to be largely consistent with the spatial distribution of
the heat stress experienced over summer. This is the fourth time in six
years that the Great Barrier Reef has been impacted by bleaching, and
it the first time it has occurred during La Niña conditions. Typically,
La Niña brings cooler temperatures to local waters.

Bleaching is a stress response by coral and does not necessarily mean
that the coral has died. Corals have a symbiotic relationship with a
type of microscopic algae known as zooxanthellae. The colorful
zooxanthellae live within the coral, providing oxygen and helping the
coral to remove wastes. In turn, the coral provides the algae with a
protected environment and the compounds they need for photosynthesis.
The zooxanthellae also provide the glorious colors that we associate
with coral. When coral become stressed—most often by a rise in ocean
temperature of as little as 1˚C—the corals expel the algae, exposing
the pale white ‘skeleton’ of the coral. This bleaching isn’t
immediately fatal to the coral, but it weakens them, opening them to
disease, starvation, and death. If conditions return to normal and the
symbiotic relationship is repaired, coral may recover from a bleaching
event.

The Great Barrier Reef Marine Park’s website stated on April 1 that
water temperatures had cooled since early March but noted that most of
the Marine Park was continuing to experience the effects of significant
heat stress. Localized weather patterns will remain critical in
determining the overall extent and severity of coral bleaching. The
website also noted that the Reef Authority is now working with its
partners to conduct in-water surveys to complement aerial surveys of
the reef. This will provide more detailed information about bleaching
intensity, mortality and depth range of bleaching impacts.

On March 31, 2022, the Moderate Resolution Imaging Spectroradiometer
(MODIS) on board NASA’s Terra satellite acquired a true-color image of
the Great Barrier Reef. The reef remains sparkling with blue tones
throughout the length visible in this image. The MODIS instrument is
quite useful for measuring Sea Surface Temperatures (SSTs), which are
correlated with coral bleaching events, but true-color images do not
usually show substantial color changes in bleaching events, as coral
sits underneath water and thus reflectivity may not change
substantially. Currently, airplane flights or inspection by diving are
more sensitive for estimating the amount of bleaching on any given
coral reef than most satellites.

Image Facts
Satellite: Terra
Date Acquired: 3/31/2022
Resolutions: 500m (151.4 KB), 250m (325.1 KB)
Bands Used: 1,4,3
Image Credit: MODIS Land Rapid Response Team, NASA GSFC



https://modis.gsfc.nasa.gov/gallery/individual.php?db_date=2022-04-04

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