Which of the following statements about plankton is true?

Plankton are a vital component of aquatic ecosystems, primarily because they serve as the foundational primary producers in many aquatic food webs. They consist mainly of phytoplankton, which are microscopic plants that utilize photosynthesis to create energy from sunlight. This process not only supports their growth but also produces oxygen as a byproduct, making them essential for maintaining the health of both aquatic environments and the atmosphere.

Phytoplankton serve as the first link in the food chain, providing energy for a wide variety of organisms, from tiny zooplankton to larger fish and marine mammals. This role establishes them as a crucial food source within the aquatic ecosystem, underscoring the importance of their existence for the survival of many marine species.

The correct statement emphasizes the role of plankton in food production, distinguishing them from other organisms in their habitat that may not contribute to the energy flow in the same way.