Photosynthetic and chemosynthetic microbes can also form symbiotic relationships with host organisms. In these locations, chemosynthetic archaea and bacteria typically form the base of the food chain. Similar to mid-ocean ridges, back-arc basins have hydrothermal vents and associated chemosynthetic communities. These communities receive much less attention than the chemosynthetic communities associated with hydrothermal vents. These organic carbon molecules suggest organisms living within the vents, harnessing chemosynthetic reactions to metabolize. In such zones, chemosynthetic microbes provide energy and carbon to the other organisms. One example is the symbiotic relationship between the tube worm "Riftia" and chemosynthetic bacteria. Due to the toxicity of , only resistant chemosynthetic bacteria survive. According to Sassen (1997) the role of hydrates at chemosynthetic communities has been greatly underestimated. These systems are largely driven by chemosynthetic derived energy. Chemosynthetic bacteria are found in benthic marine ecosystems. Bush Hill has become one of the most thoroughly studied chemosynthetic sites in the world. Chemosynthetic communities thrive where cold fluids seep out of the forearc. Chemosynthetic archaea use hydrogen sulfide as an energy source for carbon fixation, producing sugars.