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How do marine animals form mutualistic relationships with bacteria 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, certain marine animals—such as mussels, large bivalve clams, and vestimentiferan worms—form mutualistic symbioses with chemoautotrophic bacteria.12

These relationships function through the following process:

Energy Acquisition: The bacteria thrive in the warm, sulfur-rich water emitted by the vents. They oxidize sulfur (sulfide) to derive chemical energy, which they use to fix carbon dioxide into organic carbon.12
Nutritional Integration: The host animals harbor these bacteria within their bodies. By hosting the bacteria, the animals are able to derive nutrition directly from them.2

This process, known as chemosynthesis, allows these vent-dwelling organisms to serve as the primary producers for their marine ecosystem, effectively replacing the role that photosynthesis plays in other environments.12