Ocean Creatures Keep Millions of Viruses at Bay

In these virus-focused times, it's encouraging to know that many marine creatures fight viruses, including cockles. Nuttapong Photographer/Shutterstock

The rainforest has long been a cradle for virus-kind. HIV, ebola and yellow fever all started out in those lush fortresses of biodiversity.

But when it comes to harboring viruses, the rainforest has nothing on the ocean.

Scientists have tallied almost 200,000 distinct populations of viruses in the ocean, according to a study published in the journal Cell. But the actual count may run in the millions. Compare that to the several thousand viruses known to lurk in rainforests.

Plenty of those viruses don't pose a threat to humans, but for the ones that might, a surprising band of defenders has emerged. New research led by marine ecologist Jennifer Welsh from the Royal Netherlands Institute for Sea Research, suggests sea creatures play a crucial role in stemming the viral tide and maintaining a healthy balance in the sea.

"Viruses are the most abundant biological entities in marine environments, however, despite its potential ecological implications, little is known about virus removal by ambient non-host organisms," the researchers note in the paper, which was published in Scientific Reports.

Creatures that reduce viral abundance

As the paper highlights, all viruses don't get their hooks into living creatures. Some simply can't get past physical barriers erected to stop them, like shells. Other creatures use passive techniques, like filters on their feeders that don't let even the tiniest virus pass through.

The Japanese oyster filters seawater to collect nourishment — oxygen or food — and if a virus happens to get hoovered up along the way, that's fine too.

The creatures that make the biggest dent in the virus population are often tiny and not very well known. Anemones, polychaete larvae, sea squirts, crabs, cockles and sponges are the heroes that don't make the headlines.

A sponge in the Caribbean sea.
It may appear unassuming, but a sponge is the Death Star of the sea as far a viruses are concerned. Nuttapong Photographer/Shutterstock

To test their virus-fighting prowess, researchers brought 10 different animal species into the lab. Among them, sea sponges proved especially proficient at dispatching their microscopic enemies.

"In our experiments, the sponges reduced the presence of viruses by up to 94 percent within three hours," Welsh explains in a statement. "Another experiment showed that the uptake of viruses happens indeed very quickly and effectively. Even if we offered new viruses to the water every 20 minutes, the sponges remained tremendously effective in removing viruses."

Crabs proved capable combatants too, slashing 90 percent of viruses in a 24-hour span. Cockles fared less well but still eliminated 43 percent of the viruses, and oysters casually eliminated 12 percent.

Photo: John Tann [CC BY 2.0]/Flickr

However, researchers were quick to point out that the ocean is a much more volatile environment than a laboratory, with many other factors that may help or hinder these creatures.

"The situation there is much more complex, as many other animal species are present and influence one another," Welsh adds in the release.

Viruses emerging in new places

In the natural world, marine animals — much like humans — face a rising number of viruses, and some are strengthened by climate change. A 2019 study by researchers at the University of California-Davis School of Veterinary Medicine published in Scientific Reports suggests melting sea ice is adding another deadly virus to the mix: Phocine distemper virus, or PDV, which has caused extensive mortality in Atlantic seals.

"As sea ice continues its melting trend, the opportunities for this virus and other pathogens to cross between North Atlantic and North Pacific marine mammals may become more common," the study's lead author Elizabeth VanWormer noted in a press release.

If we're going to keep viruses like PDV and others at bay, we're going to have to draw a line in the sand on climate change. Along the way, we may even give marine life a boost while they're fighting the good fight.