(image Uwe Kils)
Phytoplankton (Greek phyton, "plant")) are the algal component of the plankton that drift in the water column. They obtain energy by photosynthesis, and so live mostly in the well-lit surface layer of the sea (or euphotic zone). Their cumulative energy fixation in carbon compounds (primary production) is the basis for the vast majority of oceanic (see chemosynthesis) and all freshwater food chains. One of the most remarkable and direct food-chain is phytoplankton - krill - whales.