Zooplankton refers to small, often microscopic animals that drift in aquatic environments, including oceans, rivers, and lakes. They are a crucial component of the aquatic food web, serving as primary consumers that feed on phytoplankton and are, in turn, preyed upon by larger animals such as fish. Zooplankton includes a diverse range of organisms, from tiny protozoa to larger crustaceans like copepods and krill. Their abundance and diversity play a significant role in nutrient cycling and energy transfer in aquatic ecosystems.