Due to the death and decay of the spring plankton, fresh nutrients become available in the autumn. Of course, this is a generality and the occurrence of primary and secondary plankton blooms depends on the exact geographical and climatic factors. For diatoms, silica is especially important and a limiting factor. In the Netherlands, the Oosterschelde is a favourite place for our club to collect diatoms. We can find in our Northern seas about 160 different sorts of planktonic diatoms, of which 112 are of the round type and the rest of the more elongate type.
Reproduction occurs mostly asexually.
A round diatom is a sort of pill box. Prior to division, two new box ends are formed in the middle of the cell. Separation then occurs and as a result, one of the new cells has the same size as the original cell and the other new cell is smaller than the original cell. This could result in cells getting smaller and smaller, but at a certain size the diatoms regain their size by what we call auxospore formation. Auxospore formation in Centricae is a method of sexual reproduction.