Which aquatic microorganisms eat phytoplankton and then become food for fish, crustaceans and other large species?

Zooplankton

The correct answer is option 2. Zooplankton.

The aquatic microorganisms that eat phytoplankton and then become food for fish, crustaceans, and other larger species are called Zooplankton.

Zooplankton are small, drifting organisms that feed on phytoplankton, other zooplankton, and organic matter suspended in the water. They play a crucial role in marine and freshwater ecosystems as a primary food source for various aquatic organisms, forming an essential link in the aquatic food web. Examples of zooplankton include tiny crustaceans, larval forms of larger animals, and small jellyfish.