Marine viruses are tiny infectious agents found in oceans and seas, primarily infecting marine microorganisms like bacteria and phytoplankton. They play a crucial role in regulating marine ecosystems by controlling microbial populations and influencing nutrient cycling. These viruses can impact the health of marine food webs and contribute to the overall productivity of ocean environments. By lysing (breaking down) their host cells, marine viruses release organic matter back into the water, which can be utilized by other organisms, thus supporting the marine food chain and enhancing ocean health.