Researchers have shown that the microbial populations in corals undergo changes during their winter “hibernation”

Astrangia poculata coral from Ft Wetherill, Rhode Island demonstrating facultative symbiosis. By RRotjan – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=84640526

Many creatures, from bears and squirrels to parasitic wasps and even a few fortunate humans, prepare to catch a break as winter approaches. This is also the time of year when the northern star coral (Astrangia poculata) goes into its dormant or quiescent phase. But as it sleeps, what happens to its microbiome?

Researchers at the University of California, Davis, lead by Assistant Professor Anya Brown, discovered that the coral benefits from a periodic reset as its microbial populations undergo a transition during its dormant period. Coral in warmer seas, which are more vulnerable to the effects of climate change and other environmental threats, may benefit from this research.

Dormancy, at its most fundamental, is a reaction to an environmental stressor—in this case, cold stress, as explained by Brown of the UC Davis Bodega Marine Laboratory in the Department of Evolution and Ecology. Knowing more about this recovery phase might help the researchers identify the bacteria responsible for the regeneration of coral in warmer tropical settings.

Researchers from Woods Hole Oceanographic Institution (WHOI) and Roger Williams University conducted the first study to link a persistent change in the marine organism’s microbial population to its state of dormancy. The findings were published in the journal Applied and Environmental Microbiology.

WHOI associate scientist and research co-author Amy Apprill remarked that the study reveals that microorganisms respond to stress and recover in a predictable fashion.  This information is crucial for the future development of probiotics or other microbial therapeutics for tropical corals suffering from stress.

In order to harvest 10 individual colonies of the coral A. poculata from a wharf in Woods Hole, Massachusetts, researchers plunged 60 feet down into chilly, almost 40 degrees Fahrenheit water from October 2020 to March 2021. In the Atlantic Ocean, you may find this coral everywhere from the Gulf of Mexico to Massachusetts. Cooler water temperatures cause the coral to retract its tentacles, cease feeding and reacting to touch, and enter a dormant state.

Before, during, and after dormancy, the researchers characterized the microbiomes of the wild coral. They discovered that while the coral is in its “resting” phase, its microbiome rids itself of microorganisms that thrive on nutrients and microbes linked with pathogens, while simultaneously growing microbes that may give nitrogen. They observed that this reorganization aids the corals in keeping their microbial community structure stable.

The researchers have long theorized that Astrangia’s seasonal dormancy permits the coral microbiome to reset and reorganize, acording to Koty Sharp, an associate professor at Roger Williams University and co-author on the study. Their  findings suggest a reorganization takes place during this time of inactivity, which might lead to the discovery of microbial partners critical to coral health and recovery after disturbance.

This work adds the coral A. poculata to the list of creatures known to undergo changes to their microbiomes during their inactive periods, which already includes bears, squirrels, insects, and others. The gut microbiota of the ground squirrel, for instance, is crucial to the recycling of nitrogen while the squirrel is fasting during hibernation.

The researchers said that it raises several questions.  Among the most important is this: What causes the coral to “wake up” in the early spring? This research adds to the growing body of evidence that certain microbial communities play a crucial role in the emergence from or initiation of dormancy in this coral, as well as in the management of its microbiome.

Sources:

Anya L. Brown et al. (2022). Reshuffling of the Coral Microbiome during Dormancy, Applied and Environmental MicrobiologyDOI: 10.1128/aem.01391-22

https://phys.org/news/2022-12-microbial-communities-shift-coral-winter.html