Detritivores are organisms within an ecosystem that feed on dead and decaying plant and animal material and waste (called detritus); detritivores represent more than half of the living biomass. Protozoa, polychaetes, nematodes, Fiddler crabs, and filter-feeders are a few examples of detritivores that live in the salt marsh ecosystem. (Fiddler crabs, for instance, scoop up grains of sand and consume the small particles of decaying organic material between the grains.) While microbes would eventually decompose most material, detritivores speed up the process by comminuting, and partly digesting the dead, organic material. This allows the microbes to get at such material more readily. The continuing decomposition process is vital to the existence of an ecosystem—essential in the maintenance of nutrient cycles, as well as the natural renewal of soil fertility.