Scientists have found that a surprising organism may sometimes be present when coral reefs undergo devastating bleaching events: a form of herpes virus.
In a recent paper in the journal Frontiers in Microbiology, researchers from Oregon State University describe how, while they were studying corals on Australia's Great Barrier Reef, a bleaching event began to take place. The researchers took samples of the bleaching corals and of the surrounding water, and found that the viral loads in the corals had exploded to levels 2-4 times higher than ever recorded in corals. The viruses included retroviruses and megaviruses; a type of herpes virus was particularly abundant.
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It might seem surprising to think of viruses in the context of coral reefs. But in fact marine viruses are by far the most abundant lifeforms in the ocean -- if one does consider them lifeforms, a subject of some scientific controversy. Approximately 1023 viral infections occur in the sea every second, and the approximately 1030 viruses in the ocean, if placed end to end, would span farther than the nearest 60 galaxies.
And while we may associate herpes with cold sores and awkward conversations with potential partners, herpes viruses are ancient and are found in a wide range of mammals, marine invertebrates, oysters, corals and other animals. (However, while part of the same family, herpes viruses that affect corals do not infect humans, and vice-versa.)
However, the researchers could not confirm whether the viral outbreak caused the bleaching, was a consequence of it, or took place simultaneously.
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"It's a total chicken and the egg question," Rebecca Vega-Thurber, an assistant professor of microbiology in the OSU College of Science and corresponding author on the study, told Quartz. "Did the bleaching event induce viral production, or did stress induce viruses which help induce bleaching? They're probably going on at the same time."
Indeed, the specific proximate causes of bleaching -- so-called because corals expel the symbiotic algae that live within them and give them their color -- remain uncertain, although some combination of environmental stresses certainly plays a part. The most significant appears to be increased water temperature, but others can include pollution and overfishing. The latest study suggests that, as with humans, being under stress can render corals more susceptible to infection.
"This is bad news," Vega-Thurber said. "This bleaching event occurred in a very short period on a pristine reef. It may recover, but incidents like this are now happening more widely all around the world."
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Last year, NOAA declared that the world was now experiencing its third global coral bleaching event, the previous two being in 1998 and in 2010. The current event began in the northern Pacific Ocean in 2014, moved south during 2015, and may continue into this year, NOAA officials said.
"People all over the world are concerned about long-term coral survival," Vega-Thurber said. "This research suggests that viral infection could be an important part of the problem that until now has been undocumented, and has received very little attention."