Given the task definition and input, reply with output. Given a scientific passage and an answer, generate a question for the given answer.

Passage: Algae play significant roles as producers in aquatic ecosystems. Microscopic forms live suspended in the water column. They are the main component of phytoplankton . As such, they contribute to the food base of most marine ecosystems. Answer: algae
What is the main component of phytoplankton?