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How do sulfur-oxidizing bacteria provide energy for organisms near hydrothermal vents?

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Diagram showing ocean zonation by depth and region, with labeled layers: littoral, sublittoral, bathyal, abyssal, and hadal along the seafloor, and epipelagic, mesopelagic, bathypelagic, and abyssalpelagic in open water. The littoral zone is at the high-tide mark. Vertical scale marks photic and aphotic zones from surface to 10,000 meters. — Marine ecosystem Zonation of the ocean. Note that in the littoral zone the water is at the high-tide mark.

Near deep-sea hydrothermal vents, sulfur-oxidizing bacteria serve as the foundation of the food web by performing chemoautotrophic metabolism. Unlike organisms that rely on sunlight, these bacteria derive chemical energy by oxidizing sulfur compounds, such as hydrogen sulfide ( $H_{2} S$ ), into sulfate ( $S O_{4}^{2 -}$ ).12

This process provides a vital source of organic carbon in the aphotic zone, supporting a diverse range of vent fauna. Many of these animals, including mussels, clams, and vestimentiferan worms, host these bacteria in symbiotic relationships, allowing the host to benefit directly from the bacteria's primary production. Additionally, free-living bacteria form dense, mat-like colonies on hard surfaces, which serve as a food source for various crabs, copepods, and other vent-associated organisms.1