What is the main role of zooplankton in marine ecosystems?

The correct choice highlights that zooplankton serve as primary consumers that feed on phytoplankton. In marine ecosystems, phytoplankton, which are microscopic plants, are the primary producers that perform photosynthesis and produce energy from sunlight. Zooplankton, which include a variety of small creatures like copepods and krill, consume these phytoplankton, thus playing a crucial role in the transfer of energy from primary producers to higher trophic levels in the food web.

By feeding on phytoplankton, zooplankton directly link the primary production of the ocean to larger organisms, including small fish and larger marine animals, making them an essential component of the marine food web. Their role helps sustain fish populations and supports overall marine biodiversity, emphasizing their importance in regulating marine metabolic processes and nutrient cycling.