Final answer:
The hydrothermal vent ecosystem is distinct from other ocean ecosystems due to its extremely high temperatures, and chemotrophs, rather than phototrophs, are the prokaryotes expected in such environments due to the lack of sunlight and the presence of inorganic substances for chemosynthesis.
Step-by-step explanation:
The abiotic factor that makes the hydrothermal vent ecosystem different from other ocean ecosystems is A. Temperature. Hydrothermal vents feature unusually high temperatures compared to the surrounding deep-sea environments. Here, water is superheated by magma beneath the Earth's crust and can reach temperatures up to 400°C (or 752°F), which is a stark contrast to the typically cold temperatures of the deep ocean.
In terms of metabolic needs, one would expect to find prokaryotes classified as chemotrophs at hydrothermal vents. These organisms are capable of obtaining energy by oxidizing inorganic substances, such as hydrogen sulfide, which is abundant in these ecosystems. Given the absence of sunlight deep in the ocean, phototrophs, which require light to conduct photosynthesis, would not be found here. Instead, chemosynthetic bacteria and archaea support the food web in these unique environments.