The North Sea is an example of a temperate marine ecosystem, which already now has been significantly affected by climate change and which is connected over the North Atlantic to the polar Arctic Ocean. The surface temperature of North Sea waters increased in average one degree over the past 40 years. As a consequence in the German Bight a temperature related delay of the diatom spring bloom has been identified. Furthermore, a northward movement of warm water species could be observe, e.g. Ceratium trichoceros was found only in waters south of the UK before 1970, but recently it is found off the west coast of Scotland and in the northern North Sea. In the area of the North Sea, PLANKTOSENS aims at the assessment of the diversity and abundance of plankton key species. This involves a regular analysis of the phytoplankton diversity taking advantage of molecular approaches and sensing technology.