The Biological Station Helgoland holds one of the largest and longest marine plankton time series in Europe, named 'Helgoland Roads' after the sampling location. This time series has been running continuously, with samples taken on a work-daily basis since 1962. As far as possible species counts are carried out at species level. This has allowed us to show long-term changes in abundance and seasonality of different organisms, but also to reliably demonstrate the appearance of species entirely new in the Helgoland Roads phytoplankton community. More complex analyses have also shown long-term shifts in diversity and delays in the start of the spring bloom after warm autumn/winter seasons. The latter was shown using a simple index: The mean diatom day.