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Coral’s Microbiome “Reshuffles” During Hibernation

Astrangia poculata coral species.
Microscope image of symbiotic A. poculata coral with polyps extended and microalgae. Credit: Alicia Schickle, Roger Williams University
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A new study has analyzed the microbiome of a species of coral before, during and after a period of “dormancy” during cold temperatures. The research is published in Applied and Environmental Microbiology.

“Nap” time for the northern star coral

Winter is coming, which means many creatures on Earth are preparing for hibernation – a period of rest that enables energy conservation and survival in harsh weather conditions. On land, small mammals such as chipmunks and hedgehogs scour for burrows and safe hiding spots for their long-term nap.

Under water, a species of coral – Astrangia poculata – also known as the “northern star coral” similarly experiences a period of quiescence, providing a seasonal reset. Found in the Arctic waters, A. poculata retracts its tentacles, stops eating and goes dormant when the temperature of the water drops. 

“Dormancy, at its most basic, is a response to an environmental stressor – in this case, cold stress,” says Dr. Anya Brown, assistant professor in evolution and ecology and member of the Bodega Marine Laboratory at the University of California, Davis (UC Davis). “If we understand more about this recovery period, it might help us understand what microbes may be responsible for recovering coral in warmer tropical systems.”

Brown is the lead author of a new study that questioned: what happens to the coral’s microbiome while it’s in dormancy? The research, conducted in collaboration with Woods Hole Oceanographic Institution (WHO) and Roger Williams University, is the first to characterize wild coral microbiomes before, during and after quiescence.

Coral’s microbiome “reshuffles” during rest

The scientists used 16s rRNA gene sequencing, a commonly adopted tool for studying the microbiome. From October 2020 to March 2021, they dove 60 feet down into the cold waters of a dock in Woods Hole, Massachusetts, to collect 10 distinct colonies of A. poculata, which were then sequenced upon returning to the lab.

Brown and colleagues found that, while the coral “sleeps”, it sheds copiotrophic microbes, including putative pathogens. During and after quiescence, the scientists identified an increase in bacteria and archaea that are associated with nitrification, perhaps in response to the coral not eating during dormancy. “We have long hypothesized that A.poculata’s  seasonal dormancy allows the coral microbiome to reset and restructure,” says co-author Dr. Koty Sharp, associate professor at Roger Williams University. “Our research found evidence for a shuffling during that dormant period that may help us identify microbial associates that are key to coral health and recovery from disturbance.”

“This work opens a lot of questions,” Brown adds. “A big one is: Why does the coral ‘wake up’ in the early spring? This study suggests that key microbial groups may play an important role in triggering the onset of or emergence from this coral’s dormancy and the regulation of its microbiome.”

The predictability of A. poculata’s dormancy offers a natural manipulation system to “further identify factors that regulate host-microbial associations”, the authors conclude in the paper.

Reference: Brown AL, Sharp K, Apprill A. Reshuffling of the coral microbiome during dormancy. AEM. 2022;0(0):e01391-22. doi:10.1128/aem.01391-22.

This article is a rework of a press release issued by the University of California, Davis. Material has been edited for length and content.