In the absence of sunlight, deep-sea hydrothermal vents have formed unique ecosystems, and their energy sources are completely different. This is chemical synthesis. Chemosynthesis is the process by which certain microorganisms mediate chemical reactions to produce energy. Well, animals that live near hydrothermal vents feed on chemicals that rise from the bottom of the sea from the escaping fluid. As a local food source, hydrothermal vents typically have high biomass, in stark contrast to the very rare distribution of animals outside of ventilated areas, where animals depend on food falling out of their stomachs. Chemosynthetic microorganisms provide the basis for the biological colonisation of the fountain. Chemosynthetic microorganisms live as symbionts on or under the seafloor, even in the bodies of other vent animals.