14 DAY TRIAL // You can be naughty and get cold sores around your mouth or other orifices of your body. But for corals, this is not just annoying, it is killing them. Herpes viruses and other diseases could be a main factor in the deaths of coral reefs caused by humans throughout the world, as a new research reveals.
It is well known that humans destroy corals indirectly and directly through global warming, overfishing, pollution or environmentally harmful methods of fishing (like dynamite use). Reefs close to populous coasts are usually deserted of life or threatened, and this means about 70 % of all reefs.
"For some reason, when you put people next to reefs, they die," said co-author Forest Rohwer, microbiologist of San Diego State University.
Corals reefs are the most diverse submarine ecosystems, the rainforests of the sea. They harbor thousands of species, from invertebrates like sponges, snails and starfish to a high variety of small fish like angelfish and clown fish, or big fish like parrot fish, barracuda, groupers and sharks.
"But the most amazing variety is actually found in the realm we can't see: We know [from DNA sequencing] that the most diverse things on a coral reef are actually the microbial community." said Rohwer.
"There are about 10 million bacteria and 1 billion archaea on every square centimeter of coral, and two neighboring corals can have completely different microbes living on their surfaces."
In just one milliliter of reef water, there can be one million bacteria and 10 million viruses. The microbes feed on chemical substances synthesized by algae around the reef, but usually the algae are eaten by small fishes, which are eaten by big fishes, which are food for sharks - so little is left for the germs.
"This allows the coral to actually control their microbial community by providing the food source to them through their mucous. Normally, corals use their cilia (tiny finger-like structures) to pass the bacteria along and push them off in balls of mucous that come off the corals and burst", Rohwer said.
But overfishing impairs this cycle and offers the conditions for microbes' booming, in which case they turn into pathogens. "The coral is actually losing control of its microbial community," Rohwer said.
The deadliest infections, in tests made on Panamanian corals, proved to be caused by the herpes viruses. Herpes viruses are widespread in many species (95 % of humans carry some forms and many of them are sexually transmitted).
"Everybody in this room has at least a couple herpes viruses running around. And when you get stressed, or immuno-compromised, they're going to start hopping out and giving you little cold sores or other wounds that we won't talk about. That seems to be what's going on in the corals too," explained Rohwer.