*[Enwl-eng] 'Heroic effort' as scientists race to rescue corals
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Wed Aug 30 20:00:51 MSK 2023
+ record ocean heat threatens widespread bleaching
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If this summer has felt hot for many people on land then imagine how
it has felt in the ocean, where 90% of the excess heat generated by
greenhouse gas emissions has been absorbed. El Niño, the hot phase of a
natural cycle in the Pacific Ocean which influences weather worldwide, has
amplified global heating during 2023 to make the ocean hotter than at any
other time in modern history.
As seawater in some regions has approached hot-tub temperatures,
scientists have fretted over coral reefs, ecosystems which harbour the
greatest concentration of species in the ocean. Many of these bastions of
marine biodiversity have endured overfishing, pollution and creeping
acidification. Is record ocean heat in 2023 the final straw?
You're reading the Imagine newsletter – a weekly synthesis of academic
insight on solutions to climate change, brought to you by The Conversation.
I'm Jack Marley, energy and environment editor. This week, we hear from
conservationists who are racing to save coral reefs from increasingly
hostile conditions.
Tropical coral reefs are astonishingly resilient. New research reveals
how these ecosystems – composed of tiny animal polyps in a limestone
skeleton they share with photosynthetic algae – have managed to thrive in
low-nutrient waters for millions of years.
As well as catching plankton with their tentacles and living off the
sugars their algal cohabitants make via photosynthesis, corals can eat the
algae living in their cells to acquire growth-boosting nitrogen and
phosphorous.
"This vegetarian diet allows the corals to tap into a large pool of
nutrients that was previously considered unavailable to them," say authors
Jörg Wiedenmann and Cecilia D'Angelo at the University of Southampton.
While well adapted to a challenging environment, tropical corals have
had to contend with rapid changes in recent years.
"A paper by [US] scientist Derek Manzello showed that in the Florida
Keys, the number of days per year in which water temperatures were higher
than 90°F (32°C) had increased by more than 2,500% in the two decades
following the mid-1990s relative to the prior 20 years," says Ian Enochs,
who leads coral research at a National Oceanic and Atmospheric
Administration (NOAA) lab in Miami, Florida.
"That is a remarkable increase in the number of days that corals are
experiencing particularly stressful warm water."
When corals are stressed for long enough they bleach: their colourful
algae departs and the remaining reef turns pale and can eventually starve or
succumb to disease, eroding to sand over time. A paper by Enochs' colleague
John Morris found that 70% of reefs in the Florida Keys are now eroding
faster than they are growing.
Marine heat waves (prolonged bouts of high sea temperatures) may last
weeks, but the damage they cause to reefs can be permanent. Samuel Starko at
the University of Western Australia and Julia K. Baum at the University of
Victoria studied the aftermath of El Niño-driven bleaching on Kiritimati
(Christmas Island) in the central Pacific Ocean between 2015 and 2016.
"We focused on the widespread lobed coral (Porites lobata). This
species is among the most heat-tolerant corals, and despite almost 90% of
all coral cover being lost on Kiritimati, over half of lobed corals
survived," they say.
"In fact, some Porites colonies didn’t bleach at all."
Scientists have found surprisingly hardy coral species in other
regions too. The survival of these remnants may maintain the illusion of a
healthy ecosystem – but dwindling species are a problem in their own right.
"Because interbreeding between ... lineages and species can offer a
potential avenue for future adaptation, losses of genetic diversity could
make a bad problem even worse by limiting future adaptation to changing
environments," they say.
An emergency response
The overwhelming odds against coral reefs have not deterred
researchers. Michael Childress, an associate professor of biology and
conservation at Clemson University, describes the "heroic efforts" of
scientists who sprung into action as a heat wave unravelled across the
Caribbean in June.
"Divers have been in the water every day, collecting thousands of
corals from ocean nurseries along the Florida Keys reef tract and moving
them to cooler water and into giant tanks on land," he says.
Corals can recover their algal companions if water temperatures return
to normal within a few weeks. The volunteers, students and government
scientists removing seaweed and predators encroaching reefs in the Florida
Keys and rescuing coral fragments grown in underwater nurseries could buy
these ecosystems precious time.
New research findings from reefs in the remote Pacific suggest these
efforts might not be in vain. Over 35 years, an international team of
scientists discovered that coral communities in Palau have increased their
tolerance of higher temperatures by 0.1°C a decade.
"That’s slightly less than the increase in global temperatures (about
0.18°C/decade) but does suggest these coral reefs have an innate capacity
for climate resilience," says author Liam Lachs, a PhD candidate in climate
change ecology and evolution at Newcastle University.
This means that there is a brief window in which people intervening to
limit local threats to reefs could help corals weather a peak in global
temperatures.
"But this can only improve their long-term futures if there is strong
global action on reducing carbon emissions," Lachs says.
So far, countries have not responded to the worsening plight of coral
reefs by slashing their emissions of carbon dioxide, which overwhelmingly
come from burning fossil fuels. Australia hosts the world's largest reef.
Despite being elected with a pledge to take drastic action on climate
change, its government approved a new coal mine in May.
"And still we fail to face up to the fact that the Great Barrier Reef
is dying," says Ove Hoegh-Guldberg, a professor of marine science at the
University of Queensland.
"We thought we might have had decades but it may be just years. Before
1980, no mass bleaching had ever been recorded. Since then it has only
become more common."
- Jack Marley, Environment commissioning editor
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Imagine.
The heroic effort to save Florida’s coral reef from extreme ocean heat
as corals bleach across the Caribbean
Ocean temperatures have hit record highs off the Florida Keys.
Scientists and volunteer divers are racing to save these valuable creatures.
Read more
Corals are starting to bleach as global ocean temperatures hit record
highs
Water temperatures in the 90s off Florida in July are alarming, a NOAA
coral scientist writes. Scientists in several North American countries have
already spotted coral bleaching off their coasts.
Read more
Remote Pacific coral reef shows at least some ability to cope with
ocean warming – new study
This may buy us time, but many reefs are still doomed without serious
action on climate change.
Read more
How do coral reefs thrive in parts of the ocean that are low in
nutrients? By eating their algal companions
Reef corals grow vigorously in nutrient-poor water – new research has
found out why.
Read more
Coral reefs: How climate change threatens the hidden diversity of
marine ecosystems
Exploring the often unseen, and poorly understood, nuances of
diversity within coral reefs may prove essential for ensuring the long-term
health of Earth's oceans.
Read more
Is the Great Barrier Reef reviving – or dying? Here’s what’s
happening beyond the headlines
In recent years, the Barrier Reef has had a reprieve – and coral has
regrown strongly. But now the reprieve looks to be over and the heat is back
on.
Read more
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Sent: Wednesday, August 30, 2023 8:02 PM
Subject: 'Heroic effort' as scientists race to rescue corals
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