Hydrothermal systems of deep-sea spreading centers stand out as islands of life on a seafloor where the abundance of megafauna is otherwise very low. These hydrothermal systems support a dense biomass of microbes and animals in an ecosystem that relies on chemosynthesis for energy. Hydrothermal systems are relatively rare features of the vast, deep seafloor. Current data suggest that hydrothermal systems probably occur every 50–100 km and that around 1000 systems are active at any one time (Baker and German, 2004); however, only about 10 percent of the total 60,000 km of the global mid-ocean ridge has been surveyed in any detail for the presence of hydrothermal activity. Although some individual sites cover an area the size of a football stadium and are described as being “large,” on the expanse of the seafloor they, too, represent a minute area.