Pressures on marine ecosystems are increasing due to human population growth, pollution and climate change. Monitoring of phytoplankton species occurrences is crucial to study the health of marine ecosystems, since primary producing phytoplankton forms the basis of marine food webs. Shifts in phytoplankton species distribution can indicate changes in ecosystem health. The currently used microscopic identification method for phytoplankton has limitations which can be overcome with DNA based identification methods. Combination of the DNA based, and microscopic methods will give a better assessment of the total phytoplankton biodiversity, but currently the required reference sequence databases are incomplete and incoherent. This project aims at harmonizing new DNA based methods among the Nordic countries and Baltic Sea countries at an early stage, creating guidelines on how to implement DNA based methods in phytoplankton monitoring and improve required sequence databases. Quarterly network meetings and a workshop will be organized for institutions and researchers involved in Nordic and Baltic Sea phytoplankton monitoring. The resulting guidelines will be popularized as open access podcast for the general public and published in Tema Nord or a similar open access journal.