Marine Viruses: Small Size, Large Impact

by Nicole Finnicum

Viruses have been top of mind lately – what they are, how they function, and the damage they cause.

Because we’re ocean people, we started to wonder about viruses in the ocean. Do viruses exist there? Who are their hosts? Is their biology the same? We decided to take a deep dive into marine virology and were quite surprised with what we found.

Marine viruses have only been isolated in the last 50 years, with most of the research on viral diversity beginning in the 1980s. In recent decades, scientists have learned that marine viruses are more abundant than initially thought. It turns out that marine viruses are so abundant that each and every cupful of ocean water is teeming with them. Not to worry though, these types of viruses cannot infect humans, but do infect marine life, from the large marine mammals to the smallest microbes.

This finding only came after a recent three-year study from the Tara Oceans global oceanographic research expedition. The Tara collected water samples from all over the world, from the surface of the ocean down to the deep sea with a goal to isolate new virus populations. The crew came back with an astounding number – they found 195,728 distinct viral populations in the ocean.

Technically, this make viruses the most abundant predator in the ocean.

Marine viruses are found most commonly in shallow, coastal areas and more abundant in the summer months. The Tara expedition located several viral “hot spots” in warm and temperate waters, but they also found that 40% of the viruses were found in the Arctic Ocean – a surprising discovery.

Most of the viruses isolated in this study were found to be bacteriophages – these are viruses that specifically infect bacteria, so we’re going to focus on those.

It is important to mention, however, that there are many other types of marine viruses that do infect vertebrates and invertebrates in the ocean, many of which are commercially important. Such viruses include the white spot syndrome virus of panaeid shrimp and viruses including rhabdovirus, reovirus, and nodavirus, which infect finfish. Other viruses such as the morbillivirus have had detrimental effects on harbor seals and can also infect cetaceans (whales and dolphins).

Now, back to bacteriophages – the most common type of marine virus. When a bacteriophage infects a bacterium, it attaches to receptors on the outside of the bacterial cell then injects its DNA into the host. The virus DNA replicates, forming new bacteriophages and then causes the host bacterial cell to lyse, or burst. When this burst happens, organic matter, or carbon, is released into the environment, along with new viral particles.

However, the carbon released is not available to organisms higher up on the food chain, like plankton and fish, but is instead made bio-available only to other microbes. This occurs because of a process called the viral shunt. A viral shunt is a special pathway that viruses undergo that diverts the flow of carbon back to other microbes in the ocean – essentially, a carbon recycling process.

Because viruses can redirect where carbon goes in the ocean, they are fulfilling a role in overall ecosystem functions of the ocean, specifically by regulating the availability of carbon and nutrients. This means that carbon is diverted from the traditional carbon cycle pathway and being trapped in as biomass, rather than being released into the atmosphere.

It has been suggested that marine viruses can recycle up to 150 gigatons of carbon per year, which is much more than plankton can turn over.

Scientists are currently looking at how carbon recycling by viruses can be an implication for understanding how marine viruses play into global carbon cycles and climate change. And, with the newly discovered ‘hot spots’ of viral activity in the ocean, scientists could use those spots to harness the viral activity to move carbon to be stored in the deep sea.

We are still far from understanding the implications for virology in global climate studies, but are on the path to learning more every day. This is a perfect example of how there are so many mysteries in the ocean waiting to be discovered and that many of those mysteries remain unseen to the naked eye.


Finnicum is the Operations Manager at Sanibel Sea School. Part of the SCCF (Sanibel-Captiva Conservation Foundation) Family, Sanibel Sea School’s mission is to improve the ocean’s future, one person at a time.

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