What do baby oysters eat, and how do they eat it?

Baby oysters eat algae by filtering seawater through their gills (sort of like a whale filtering water through its baleen to get shrimp). Algae is a microscopic plant that grows in water, so the oyster is a vegetarian, or plant eater. In fact, oysters eat only algae, or phytoplankton, through their entire life. A good sized adult oyster can filter some 80 Litres of water per day, and if every litre contained thousands of tasty, digestible bits of algae, you can imagine the process.