Bacterioplankton - The second group namely zooplankton consists mainly of protozoans which feed on phytoplanktons, bacteria and detritus. Zooplanktons are found in regions just below that of phytoplanktons they try to escape from light and sink to the bottom regions. During night they come to the surface Zooplanktons are motile forms with cilia or flagella and show vertical migration.
During day time and feed on their prey. Thus they exhibit a diurnal migration. Sometimes, bacteria in the water column may be considered as a separate planktonic group which are called bacterioplankton.
