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Koty Sharp emerges from the ocean off the coast of Fort Wetherill, Rhode Island, and walks onto the rocky beach. She's wearing scuba gear and carrying a red mesh bag. Sharp is an ecologist at Roger Williams University in nearby Bristol, and the red bag holds a treasure.
She opens it for inspection. "This what a coral colony looks like, here in Rhode Island," says Sharp, gazing fondly into the bag. Inside there are about 30 small gray rocks, each about the size of a quarter. The rocks appear to be covered with snot.
"It’s not as charismatic as tropical corals, we will definitely accept that," says Sharp. "But these stand to tell us a lot of basics about corals."
This tough, tiny coral — which is much prettier underwater, Sharp insists — is called the Northern Star. It's a temperate species that grows all along the East Coast, from Buzzards Bay to the Gulf of Mexico. It's New England's only native hard coral, and it has a lot to teach scientists about its tropical cousins.
"Most people are surprised to find out that there are corals in New England, and that’s why we think this is so special," says Sharp. "It’s a really peculiar and, I would argue, important organism. Because it is able to live up here in New England, and survive cold winters and very warm summers, it has some properties that other corals — especially those in the tropics — don’t have, and we can learn more about how corals function in response to temperature by studying this coral."
Most tropical corals can survive only a small, temporary shift in temperature. Scientists predict that virtually all tropical coral reefs will disappear if Earth warms by 2 degrees Celsius.
Sharp is one of a handful of researchers studying the Northern Star — known to scientists as Astrangia poculata — with the hope that it might offer a better understanding of basic coral biology and strategies to help protect endangered tropical coral reefs. Many of them work under the umbrella of the Astrangia Research Working Group, which is co-led by Sharp, Sean Grace of Southern Connecticut State University and Boston University ecologist Randi Rotjan.
Rotjan has been studying corals for more than a decade, and has a special place in her heart for the Northern Star.
"It's a strange one," she says. "It's a hard, calcified coral, but it doesn't get bigger than your fist. It grows up and down the East Coast of the U.S. primarily, but it can grow from the intertidal down to at least a couple hundred feet, maybe even a little deeper, which gives it a really wide range. But in the shallowest parts of its range it's really special."
Special, says Rotjan, because they can survive "bleaching," which kills many tropical corals.
Little organisms that live inside coral — called symbionts — use photosynthesis to make sugar, which they feed to the corals in exchange for a place to live. It's the symbionts that give tropical corals their brilliant colors. When the symbionts leave — usually because the water gets too hot for too long — the corals are "bleached" translucent or white.
"When corals bleach it sort of sets a clock ticking," Rotjan says. "When the symbionts leave they start to starve. And if the symbionts don't come back in time they starve to death."
But not the Northern Star. Unlike tropical corals, our scrappy little coral survives bleaching. In fact it often looks bleached but is perfectly healthy. That’s partly because it’s figured how to feed itself when the symbionts aren't around. But that’s not the whole story, and nobody knows the full secret to its survival. Yet.
Sharp has found that the Northern Star changes its microbiome with the seasons. And she suspects that the coral’s unique way of hunkering down during the winter and reemerging in the spring may offer a parallel to tropical corals trying to recover from heat stress or bleaching.
To understand this process better, Sharp wants to study the entire life cycle of the Northern Star, raising it from single cells to adulthood.
Sharp says it’s a lot of work to raise Astrangia from scratch, and grow larvae into adult colonies in the lab. Her team has done this a couple times on a very small scale, but now they're trying to scale it up. If her team can pull it off, they’ll be the first in the world to do it.
"Getting these earliest life stages tell us a lot about what controls symbiosis in these corals, when they first acquire the beneficial microbes that keep them alive, and that we think are really important for their survival in the ecosystem," says Sharp. "We think it's actually the key to their resilience."
The scientists hope that learning the basic biology of the Northern Star will prove useful for all coral researchers. "A temperate coral is not a tropical coral, but because they have so many similarities we can learn a lot," says Rotjan, who likens Astrangia to a "mouse model" for corals. "We've made major breakthroughs in our understanding of human biology and physiology [and] human medicine by using mice, but nobody would ever claim that a mouse is a human. But we've still learned a ton and it's the same here. It's a really good mouse model for us."
Rotjan says interest in the Northern Star has grown in recent years, perhaps because tropical corals are under such threat.
"We're living at a time when corals are really important and need more help and attention in science and study," she says. "And this coral has a lot to teach us."
This segment aired on August 23, 2019.
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