Pangea split during the Jurassic Period. There were dinosaurs in the Jurassic Period, which went extinct in the Cretaceous Period. Conifers and ferns were present in the Jurassic Period, but not in the Cretaceous Period.
The thing that would most likely to happen if the phytoplankton in the ocean were reduced is that the amount of carbon dioxide will increase since these plants are the one who is consuming most CO2 in the water.
The plant will wilt because the concentration of water in saltwater is lower than the concentration of water in the plant itself (because it is a freshwater plant). Water will diffuse out of each individual cell and the cell will crenellate (or shrivel up) causing the plant to wilt.
