Aquatic microbes play an important role in the cycling of nutrients throughout water ecosystems. They promote decomposition by breaking down dead plants and animals. This leads to the release of nutrients into the water. In addition, microbes serve as food for animals, such as marine worms that eat bacteria and fungi living in the aquatic sediments. One of the most important roles of aquatic microbes is the production of oxygen by phytoplankton. These microbes release oxygen as they harness the energy of the sun during photosynthesis.