The dataset corresponds to the diatom plankton count recorded from 1907 in Helgoland Roads. The original data set was handwritten in paper sheets to be found at the AWI library collection. Original counts were recorded in German as: Selten (s), Vereinzelt (v), Nicht selten (n.s.), Häufig (h), sehr häufig (s.h.) and massenhaft (m). Data was digitized and converted into an English scale and then into numerical data as follows:Not present (-): 0selten (s) - rare (r): 1vereinzelt (v) - occasional (o): 2nicht selteen (n.s.) - not rare (n.r): 3häufig (h) - common (c): 4sehr häufig (s.h.) - very common (v.c): 5massenhaft (m) - mass bloom (m): 6* Cells left in blank correspond to species not found by the time, but encountered later the year