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Better understanding of coral-algae relationship could help prevent bleaching

By
Brooks Hays
Symbiotic algae is seen growing inside the coral polyps of Acropora tenuis. Photo by Katarina Damjanovic
Symbiotic algae is seen growing inside the coral polyps of Acropora tenuis. Photo by Katarina Damjanovic

May 13 (UPI) -- To better protect coral reefs, scientists suggest an improved understanding of the coral-algae relationship is necessary.

During coral bleaching events, environmental stress triggers a breakup of the symbiotic relationship between coral and algae.

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In a new study published in the journal Trends in Ecology and Evolution, scientists argue most of the research into coral bleaching have focused exclusively on coral. The study's authors call for an increased focus on the algae that house themselves inside coral skeletons.

"Little is known about the molecular mechanisms underlying their symbiotic relationship -- how can we understand the break-up if we don't understand the relationship in the first place?" Cheong Xin Chan, a researcher at the University of Queensland and its Institute for Molecular Bioscience, said in a news release.

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Chan and his colleagues want to figure out why algae abandon coral when the going gets tough -- when temperatures rise and acidity levels rise. They also want to find out why some algae and their coral partners are more resilient than others.

The algae that partner with coral are dinoflagellates, a group of phytoplankton. The algae get shelter from coral, while the coral usurp some of the energy algae harvests from sunlight via photosynthesis.

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"This algae family is very diverse," Chan said. "Some are toxic, causing the harmful algal blooms known as 'red tides', while others provide bioluminescence or grow in sea ice, and many are free-living."

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To learn more about these phytoplankton, Chan and his colleagues are sequencing the genomes of as many species as they can, searching for genes responsible for qualities like resilience and adaptability.

But figuring out how to unravel and study algal genomes is a challenge in and of itself.

"Nothing is straightforward with these algae as they have some of the weirdest genomes we've ever seen," said IMB researcher Raul González-Pech. "In a human cell, the DNA is organized into 23 pairs of chromosomes but the DNA of these algal cells is so tightly packed that we still don't know exactly how many chromosomes they have."

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Chan, González-Pech and their research partners are making progress. They have already sequenced the genomes of nine algae species in just four years. The team of researchers is currently working to compare the genomes of coral-loving algal species with those of free-roaming or solitary species.

"Dinoflagellates are vital for the survival of Australia's Great Barrier Reef," Chan said. "We can use genomic information to address fundamental questions of what makes these algae successful symbiotic partners in the coral reefs, for example, how they contribute to heat-resistance in certain corals more than others."

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