Have you ever found flintstone on the beach? You probably didn't realize that the stone was once millions of one-celled diatoms! Diatoms form an important group within the marine phytoplankton. They are capable of fixing lots of energy from the sun, making them an important source of food for plankton feeders, such as worms, copepods and fish larvae. In turn, these small animals are food for larger animals, such as fish. Diatoms make up the base of the food web in the sea. Depending on the species, diatoms live in the water as well as on the bottom of the sea. They don't grow larger than several tenths of a millimeter.