California: As winter approaches, many animals hunker down for some much-needed rest, from bears and squirrels to parasitic wasps and a few lucky humans.
During this time, the northern star coral (Astrangia poculata) also enters a dormant state known as quiescence. However, what happens to its microbiome while it sleeps?
A study by Assistant Professor Anya Brown of the University of California, Davis discovered that microbial communities shift as this coral enters dormancy, providing it with an important seasonal reset. The findings could have ramifications for coral in warmer waters dealing with climate change and other environmental issues.
"Dormancy, at its most basic, is a response to an environmental stressor -- in this case, cold stress," said Brown, who is part of the UC Davis Bodega Marine Laboratory in the Department of Evolution and Ecology. "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."
The study, published in the journal Applied and Environmental Microbiology with scientists from Woods Hole Oceanographic Institution, or WHOI, and Roger Williams University, is the first to demonstrate a persistent microbial community shift with dormancy in a marine animal.
"This study shows that microbes respond to stress and recover in a predictable pattern," said co-author Amy Apprill, an associate scientist at WHOI. "It's foundational knowledge that may help us develop probiotics or other microbial treatments for stressed tropical corals."
Researchers dove 60 feet into cold, nearly 40-degree Fahrenheit water from a dock in Woods Hole, Massachusetts, from October 2020 to March 2021 to collect 10 distinct colonies of the coral A. poculata. This coral can be found in the Atlantic waters from the Gulf of Mexico to Massachusetts. When the temperature of the water drops, the coral retracts its tentacles, stops eating and responding to touch, and goes dormant.
The researchers studied the microbiomes of wild corals before, during, and after dormancy. They discovered that while the coral "sleeps," its microbiome sheds nutrient-loving and pathogen-associated microbes while increasing microbes that may contribute nitrogen. The scientists discovered that this restructuring aids corals in maintaining the structure of their microbial communities.
"We have long hypothesized that Astrangia's seasonal dormancy allows the coral microbiome to reset and restructure," said co-author 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."
Why does coral wake up?
With this study, a marine species -- the coral A. poculata -- now joins bears, squirrels, crickets and others on the list of animals that have microbiomes that shift while they are dormant. For example, the ground squirrel's gut microbiome plays an essential role in nitrogen recycling while the squirrel fasts during hibernation. "This work opens a lot of questions," Brown said. "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." —ANI