Step 1: Deep sea hydrothermal vents are located in regions where sunlight does not reach.
Step 2: In the absence of sunlight, photosynthesis is not possible.
Step 3: Primary producers in these ecosystems obtain energy by oxidizing inorganic substances such as hydrogen sulfide.
Step 4: Such organisms are known as chemolithotrophic bacteria.
Hence, the primary producers in deep sea hydrothermal vents are chemolithotrophic bacteria.