Final answer:
Benthic invertebrates, sea ducks, and bivalves are all organisms that feed on phytoplankton; the first two are more mobile and may actively seek it out, while bivalves filter it from the water as they feed.
Therefore, bivalves is the correct answer.
Step-by-step explanation:
The organisms that feed on phytoplankton include a variety of marine life, spanning different trophic levels and ecological niches. Among the consumers of phytoplankton are benthic invertebrates, which are organism that crawl in sediments at the bottom of a body of water and can include species such as clams that are filter feeders, actively removing plankton from the water column. Sea ducks are higher order predator vertebrates (phylum Chordata) which may find food in the waters by using taste or chemical cues to find prey, including phytoplankton. Another important group of phytoplankton feeders are bivalves, such as oysters and mussels. These creatures are efficient filter feeders, which means they consume plankton as they filter water for nutrients, thereby playing a crucial role in controlling phytoplankton populations and the clarity of the water.