When a virus infects a cell, it hijacks its biosynthetic machinery to replicate, turning it into a sort of virus factory, until it causes the cell to rupture: a process known as viral lysis. Besides producing new viruses, rupturing the host cell releases cellular components into the water as dissolved organic matter. 
This matter becomes readily available food for other microorganisms, which in turn will be eaten by larger organisms. Through this mechanism, known as the viral shunt, viruses recycle nutrients, fueling the base of the marine food web. 

Through lysing their hosts, these tiny ocean inhabitants also play a key role in transporting carbon to the seabed, helping to mitigate climate change. 

When the infected cell ruptures, large, sticky molecules known as TEPs (Transparent Exopolymer Particles) are also released. These gelatinous particles easily aggregate with other debris, mucus, and fecal pellets, forming what is known as “marine snow“: visible flakes of organic matter that slowly sink towards the deeper layers of the ocean. This process, called the viral shuttle, acts as an “elevator” that transports organic matter (and therefore carbon) to the ocean depths, helping to store it in the seabed and effectively removing it from the atmosphere. Studying the role of viruses in the carbon cycle is crucial for better understanding how oceans behave under the pressure of climate change.

Marine viruses can move genes among different organisms through a process known as “horizontal gene transfer”.
During the process of viral infection and replication, fragments of the host’s DNA can be accidentally packaged into new viral particles and then transferred to another host upon infection. This genetic exchange accelerates the pace of evolution, allowing microbial communities to adapt rapidly to environmental changes. This genetic reshuffling is particularly important in the deep ocean, where it enables microorganisms to survive in extreme and variable conditions.

Marine viruses represent an extraordinary resource for biotechnology, as they are considered the largest unexplored reservoir of genetic diversity on our planet. Most of the genetic properties of marine viruses are still unexplored, but recent discoveries have highlighted innovative features that could lead to significant advances in different fields, including medicine, materials science, and cosmetics.

A promising application is phage therapy, which uses bacteriophages (or phages), that are viruses that specifically infect bacteria, to fight off bacterial infections.
Marine bacteriophages stand out as some of the most promising and safe options for fighting infections, thanks to their remarkable specificity, strong lytic activity, and ability to adapt to extreme aquatic conditions. This approach is particularly relevant in aquaculture, a sector where the overuse of antibiotics is a growing concern.

Far from being mere pathogens, marine viruses play crucial roles in the marine environment by regulating microbial community composition and diversity, recycling nutrients, and influencing biogeochemical cycles. Despite being incredibly numerous, most of these viruses are harmless to humans and are, in fact, essential for the balance of marine ecosystems.