The "tube worms" get their metabolic energy by drawing in carbon dioxide and hydrogen sulfide from the hot spring fluids and providing it to symbiotic bacteria inside their bodies. The warm fluid flowing from the fractures in the rocks is seawater that has flowed a kilometer or so down into the crust encountering molten magma at depth, heated to high temperatures then quenched by mixing with cool water while ascending. The fish hang out in this deep sea spa because they are the top of a food chain, with the primary productivity provided by chemosynthetic bacteria, which get their energy from the chemical reactions of the hot spring fluids. (photo by John Edmond, sitting next to me in ALVIN)
These hot springs, driven by the flow of energy outward from the interior of the earth, are elegant examples of what Ilya Prigogine calls Dissipative Structures. The flow of thermal energy, and earth's gravity, provide constraints, and the collective properties of water molecules produce convection cells.
Extension of this concept of "self-organizing" bahavior - the emergence of order, the coherent behavior of collections of molecules in this case, from chaos, under the influnce of a flow of energy and appropriate constraints - leads to the notion that similar hot springs on the floors of the earth's first oceans were the site of the origin of life on Earth.
The Origin of Life