source of new energy into the ocean ecosystem. It is possible that sinking diatoms are an important source of energy for deep ocean ecosystems. Attached diatoms are also eaten by animals that graze on the wide variety of surfaces on which diatoms grow, including the blades of seagrass and kelp, mudflats, sandflats, "bare" rock and on the shells of other animals such as molluscs. How do they grow and reproduce? Under the right conditions, diatoms can reproduce very rapidly and a population of a small species can double each day. Diatoms normally reproduce by binary fission, where one 'mother cell' splits into two daughter cells. The two halves of the mother frustule become the 'lids' for the daughter frustules- the 'box' parts are made inside, as the daughters separate. One daughter cell will therefore be the same size as the parent, and the other will be slightly smaller. Over time, a lineage of diatoms will get smaller and smaller, although a few species avoid this problem by having stretchable frustules. When cells get too small, they discard their old frustules and build new, much larger ones. This process can be connected to sex. In many centrics, some individuals will break up into many small sperm-like cells. These 'fertilise' other diatoms, which then produce new, large frustules. In pennates, 'sex' involves two adult cells lining up alongside each other, dividing and then swapping one daughter cell each. The new pairs of daughter cells fuse, giving two cells that are each half