Weegy: They need sunlight and water to survive. [ Two special adaptations phytoplankton have to stay in the photic zone:
Light weight - diatoms are made of silica which is a lightweight material they use to make up their thecas.
Flagella - dinoflagellates use two flagella to move about the water column and move towards areas of higher UVA/UVB concentrations. ] (More)