What is definition of planktonic?

Planktonic refers to organisms that drift or swim in the water column, unable to maintain their position against water currents. These organisms can be microscopic or large, single-celled or multicellular, and include algae, bacteria, protozoa, and small animals such as copepods, krill, and jellyfish. Planktonic organisms form the base of many marine food chains and play a critical role in the ocean's biogeochemical cycles. They are classified into two main groups: phytoplankton (plants) and zooplankton (animals). Planktonic organisms are important indicators of water quality and environmental health, and their distribution and abundance can be used to monitor changes in marine ecosystems.