Krill eat phytoplankton, which can technically be considered seaweed but also it is considered algae too. Phytoplankton are plant plankton. Zooplankton are animal plankton. Phytoplankton include seaweed and algae. Phytoplankton are mostly made up of diatoms and dino flagellates. Diatoms are microscopic, single celled plants covered by two shells that look glossy. Dino flagellates are tiny plants with white shells all over them. The shells have a whip like motion that allows the phytoplankton to move.