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‘Dead Corals Don’t Make Babies’: New Great Barrier Reef Coral Growth Declined 89% After Back-to-Back Bleaching Events

Oceans
Coral bleaching at Lizard Island on the Great Barrier Reef in March 2016. The Ocean Agency / XL Catlin Seaview Survey / Richard Vevers

The back-to-back coral bleaching events that damaged two-thirds of Australia's Great Barrier Reef in 2016 and 2017 have had a lasting impact on the health of the largest living structure on earth.

A study published in Nature Wednesday found that the death of corals in 2016 and 2017 has significantly decreased the ability of new corals to grow and thrive. In 2018, there has been an 89 percent decline in the number of new corals on the reef compared to the historic record.

"Dead corals don't make babies," lead author and James Cook University professor Terry Hughes said, as BBC News reported.


The researchers, from the ARC Center of Excellence for Coral Reef Studies in Australia, were surprised by the extent of the decline in new corals. It was the first time they had observed such a decline on the reef.

"We thought the Barrier Reef was too big to fail," ARC chief investigator Andrew Baird told The New York Times, "but it's not."

Baird added that the study was the first to document the collapse of the processes of an ocean ecosystem.

Bleaching occurs when warm water forces corals to expel the algae that gives them color and nutrients. Reefs can recover from such events, but it takes about a decade. The Great Barrier Reef has suffered four since 1998 and, if greenhouse gas emissions continue at current levels, there could be two bleaching events every decade beginning in 2035.

The extent of the most recent bleaching events — covering 900 miles of reef — also made it harder for baby corals to replenish impacted coral populations, BBC News explained.

"Babies can travel over vast distances, and if one reef is knocked out, there are usually plenty of adults in another reef to provide juveniles," Baird told BBC News. "Now, the scale of mortality is such that there's nothing left to replenish the reef."

The bleaching impacted some corals more than others. New Acropora corals decreased by 93 percent. These are table-shaped corals that are responsible for the three-dimensional structure of the reef and provide habitat for species like coral trout and clown fish.

"We've always anticipated that climate change would shift the mix of coral," Hughes told National Geographic. "What's surprised us is how quickly that is now happening. It's not happening in the future. It's something that we're now measuring."

A 2018 study had provided some hope by finding that corals that survived the 2016 bleaching event were also better able to withstand the event in 2017. Researchers are trying to breed the more resilient corals, but National Oceanic and Atmospheric Administration's Coral Reef Watch coordinator Mark Eakin, who was not involved in the study, told The New York Times that projects like this could not replenish the whole reef.

"Those are at the scale of a large family garden," he said, while the threat to the Great Barrier Reef could cause "the loss of an entire seascape."

Baird seemed to agree.

"We've gotten to the point now where local solutions for the reef are almost pointless―the only thing that matters is action on climate change," Baird told BBC News.

Coral bleaching at Heron Island on the Great Barrier Reef in January 2016.

The Ocean Agency / XL Catlin Seaview Survey / Richard Vevers

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Farms with just one or a handful of different crops encourage fewer species of pollinating and pest-controlling insects to linger, ultimately winnowing away crop yields, according to a new study.

Up to half of the detrimental impacts of the "landscape simplification" that monocropping entails come as a result of a diminished mix of ecosystem service-providing insects, a team of scientists reported Oct. 16 in the journal Science Advances.

Monocrop palm oil plantation Honduras.

SHARE Foundation / Flickr / CC BY-NC 2.0​

"Our study shows that biodiversity is essential to ensure the provision of ecosystem services and to maintain a high and stable agricultural production," Matteo Dainese, the study's lead author and a biologist at Eurac Research in Bolzano, Italy, said in a statement.

It stands to reason that, with declines in the sheer numbers of insects that ferry pollen from plant to plant and keep crop-eating pests under control, these services will wane as well. But until now, it hasn't been clear how monocultures affect the number and mix of these species or how crop yields might change as a result.

Aiming to solve these questions, Dainese and his colleagues pulled together data from 89 studies cutting across a variety of landscapes, from the tropics of Asia and Africa to the higher latitudes of northern Europe. They tabulated the number of pollinating and pest-controlling insects at these sites — both the absolute number of individuals and the number of species — along with an assessment of the ecosystem services the insects provided.

In almost all of the studies they looked at, the team found that a more diverse pool of these species translated into more pollination and greater pest control. They also showed that simplified landscapes supported fewer species of service-providing insects, which ultimately led to lower crop yields.

The researchers also looked at a third measure of the makeup of insect populations — what they called "evenness." In natural ecosystems, a handful of dominant species with many more individuals typically live alongside a higher number of rarer species. The team found as landscapes became less diverse, dominant species numbers dwindled and rare species gained ground. This resulting, more equitable mix led to less pollination (though it didn't end up affecting pest control).

"Our study provides strong empirical support for the potential benefits of new pathways to sustainable agriculture that aim to reconcile the protection of biodiversity and the production of food for increasing human populations," Ingolf Steffan-Dewenter, one of the study's authors and an animal ecologist at the University of Würzburg in Germany, said in the statement.

The scientists figure that the richness of pollinator species explains around a third of the harmful impacts of less diverse landscapes, while the richness of pest-controlling species accounts for about half of the same measure. In their view, the results of their research point to the need to protect biodiversity on and around crops in an uncertain future.

"Under future conditions with ongoing global change and more frequent extreme climate events, the value of farmland biodiversity ensuring resilience against environmental disturbances will become even more important," Steffan-Dewenter said.

Reposted with permission from our media associate Mongabay.

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