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Beneath the ocean’s surface lie delicate multicolored cities covering less than 1% of the ocean’s floor. Despite its fragile skeletal exterior, coral sustains over a quarter of all marine life.
Reefs also are the foundation of many coastal communities, providing essential foods, medicine and protection from natural disasters for more than 1 billion people, a new report from the Global Coral Reef Monitoring Network found.
However, the colorful ecosystems are increasingly in danger as rising sea temperatures cause large-scale bleaching events, with a progressive loss of about 14% of the world’s reefs between 2008 and 2019, according to the study released earlier this month.
While Hawaii’s reef spans over 410,000 acres, the islands have lost nearly 7% of their hard coral cover over the past 10 to 15 years, the GCRMN report found. And during the state’s last extreme bleaching event in 2019, some reefs experienced as much as 55% live coral loss, according to the Department of Land and Natural Resources.
“There’s not a lot we can do to change ocean conditions back to where they were 30-40 years ago in terms of heat stress and ocean acidification,” said Jennifer Koss, director of the National Oceanic and Atmospheric Administration’s coral reef conservation program.
Despite the alarming reports, scientists remain hopeful that the reef devastation can be reversed as they seek ways to help coral, which is an invertebrate animal, evolve and acclimate to rapidly warming waters, starting with its microscopic genetic composition.
Fascinated by genetics in high school, Czech Republic native Eva Majerova was the first in her family to have the option of choosing what she wanted to study in college after the fall of the communist regime in 1989.
She eventually chose molecular biology and genetics, and ended up in Brussels where she did cancer research, trying to understand what makes cancer cells immortal.
After nearly 10 years, she applied to the Ruth Gates Coral Lab — now known as the Coral Resilience Lab — hoping to answer a similar question after noticing that some corals thrived while others died in similar circumstances.
“I basically do the very same with cancer as I do with corals,” Majerova said. “I’m trying to figure out how it is possible that these more resilient corals don’t die or don’t bleach.”
In March, Majerova and her colleague Crawford Drury released a final version of their research paper — funded by the Paul G. Allen Family Foundation and the Annenberg Foundation — although it’s still awaiting peer review.
Majerova worked with the late Ruth Gates — the former director of Hawaii’s Institute of Marine Biology — and found that corals could acclimate to higher temperatures after consistent off and on exposure to heat.
Now, she’s using a tool that has been shown to be effective in helping to fight and prevent cancer: antioxidants.
For corals, she used an antioxidant called mannitol — a plant sugar that mimics antioxidants produced by the coral — to decrease bleaching when placed in a hotter environment.
“I like to read a ton of literature from human research and I try to apply it to corals,” she said.
In her study, she took seven colonies of coral from different depths in Kaneohe Bay and analyzed the samples in a lab on Coconut Island, a private research center on the Windward side of Oahu.
She had four groups: a control group maintained at 26 degrees Celsius, a preconditioned group that was alternated between the control temperature and 29 degrees Celsius for 72 hours at a time for two weeks, non-preconditioned coral and non-preconditioned coral that were given mannitol under heat stress.
After subjecting all experimental corals to extreme heat stress — 32 degrees Celsius for 72 hours — the non-preconditioned corals were almost completely bleached while the pre-conditioned coral and non-preconditioned coral with mannitol showed very mild signs of damage.
Looking beyond physical color differences, Majerova found much higher DNA damage to non-preconditioned coral compared to the other two experimental groups.
The study concluded that the antioxidant mannitol helped a non-preconditioned coral behave as if it had acclimated after weeks of on-and-off heat exposure.
Majerova isn’t the only researcher racing to understand the molecular biology of coral. The GCRMN dataset included the work of more than 300 scientists across 73 different countries.
Phillip Cleves, a principal investigator with the department of embryology at the Carnegie Institution of Science, explained that he’s been spawning coral in a basement lab in Baltimore and using the first type of genetic engineering in coral to allow coral gene disruption.
“We think that by just generating clearer insights into how corals work at the molecular level, this will make us better at understanding what’s going to happen and if there’s anything we can do to help them,” he said.
Cleves said he hopes to understand the genes and pathways that corals use to make them either susceptible or resistant to bleaching, and to use that information to build a platform to identify naturally resilient coral.
But he said that researchers have been working to understand coral on a molecular level for decades and still don’t have all the answers.
“If you read the primary literature, you can find maybe a half a dozen different possible mechanisms for why corals bleach,” Cleves said. “Some people think it’s immune-related, some people think it’s nutrition, some people think it’s due to reactive oxygen; however, despite our efforts to understand this deeply, we don’t have a clear idea of what gene pathways cause bleaching.”
Coral has a symbiotic relationship with algae, which provides its color and allows them to produce oxygen and energize.
However, Majerova said excessive heat stress causes the symbiotic algae to overexcite and overproduce oxygen or “free radicals” that damage the coral’s DNA. The coral then evicts the algae, causing itself to bleach.
“Symbiont is not like this friendly organism anymore, but it is recognized as something harmful — it is recognized as if it was a harmful bacteria and the coral gets rid of it,” she said.
University of Hawaii professor Robert Toonen said a lot is still unknown.
“We still do not know who is in charge,” he said. “Is it the coral animal? Or is it the algal symbionts?”
Rather than focusing on microbiology, Toonen studies the thousands of organisms that make coral reefs functional. He conducts research to predict coral response under different conditions like ocean acidification and extreme warming events.
“My personal belief is that we could never scale up what we are doing — where we are manipulating antioxidants or captive breeding of corals — to the scale that we can transplant across the entire planet,” Toonen said.
Koss welcomed what she called unprecedented collaboration in the coral community.
“There’s been a lot more investment globally into restoration, into threat abatement and quantifying the benefits of corals,” she said. “I would say that we’re making good progress and we’re understanding the innate resilience of corals in ways that we didn’t before.”
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