Light and photosynthesis
Light zones in the ocean
Plants in the ocean produce over half the world's oxygen.
The most important plants in the ocean are too small to be seen without a microscope.
They float near the surface and drift with the currents, so they have been named phytoplankton (phyto=plant, plankton=drifter).
Phytoplankton are the 'grass' of the sea. Where they grow there is food for marine animals.
Ocean colour tells you how much phytoplankton there is in the water.