Year-to-year variation in the occurrence of some dominant phytoplankton species in Dutch coastal waters, 1973–1984

The surface water layer of a 70 km wide area along the Dutch coast has been sampled monthly from (February) 1973 to (August) 1984, as part of a water quality assessment research. The blooming periods of phytoplankton algae studied, fluctuated from year-to-year, but diatom blooms increased in length in the late 1970s. Dinoflagellates decreased in cell numbers in the same period. The observation of highest cell numbers of some diatoms and dinoflagellates in the lower salinity near coastal waters can be explained by eutrophication effects.