Herpes strains found to be common in reef ecosystems
By Summit Voice
SUMMIT COUNTY — After finding that bacteria from waste water effluent are a major factor in the elkhorn coral die-off in Florida’s coastal waters, researchers are focusing on other pathogens that may be affecting reefs, including viral disease.
“We have found that nutrient increases from pollution can cause increased levels of viral infection, as do warmer water and physical handling,” said Rebecca Vega-Thurber, an assistant professor of microbiology at Oregon State University. “Now we have to determine if those increases in infection cause actual diseases that are killing the coral.”
One of the surprises from recent research was the predominance in corals of herpes viruses – similar but not identical to the herpes virus that can infect humans. Herpes viruses appear to constitute a majority of the viruses found in corals, and one experiment showed that herpes-like viral sequences were produced in coral tissues after acute episodes of stress.
“We were shocked to find that so many coral viruses were in the herpes family,” Vega-Thurber said. “But corals are one of the oldest animal life forms, evolving around 500 million years ago, and herpes is a very old family of viruses that can infect almost every kind of animal. Herpes and corals may have evolved together.
“Coral abundance in the Caribbean Sea has gone down about 80 percent in the past 30-40 years, and about one-third of the corals around the world are threatened with extinction,” Vega-Thurber said.
“We’ve identified 22 kinds of emerging disease that affect corals, but still don’t know the pathogens that cause most of them,” Vega-Thurber said. “Most researchers have looked only at bacteria. But we suspect viruses may play a role in this as well, and it’s important to learn more about what is causing this problem. Corals are the building blocks of the tropical seas.”
A research program at OSU, one of only two of its type in the world, is studying viral “metagenomics” in corals, meaning the analysis of multiple genomes at the same time. It may help explain one of the underlying causes of coral decline, and is one of the most comprehensive analyses yet done on the types of viruses in a marine animal. It may also shed light on the broader range of viruses that affect not only corals but many other animals, including humans.
It’s not yet certain, researchers say, whether the viruses being found on corals are actually causing diseases.
“Just because you harbor a virus doesn’t mean you are getting sick from it,” Vega-Thurber said. “This is part of what we have to pin down with further research.”
Some of the possible causes of coral decline that have been identified so far include global warming that causes coral bleaching, loss of symbiotic algae that help nourish corals, pollution such as sewage runoff, and human-coral interactions.
A “mucus” sometimes found on corals can harbor human-borne viruses, and levels of these viruses have been correlated with terrestrial human population density.
Corals are often a major component of marine ecosystems and biodiversity, especially in the tropics. They host thousands of species of fish and other animals. And whether or not viruses are implicated in coral disease, it may also be that they are passing diseases along to fish.
The research was recently published in the Journal of Experimental Marine Biology and Ecology. Further studies are “likely to reveal that viruses have numerous and profound roles on coral reefs,” the scientists said. “As the diversity, distribution and function of reef-associated viruses becomes increasingly well defined, so will our ability to predict, prevent and/or mitigate disease epizootics on coral reefs, they concluded.