Photosynthetic picoplankton constitutes a large fraction of the primary producers in the Baltic Sea. Microdiversity widespread in the group that consist of both photosynthetic picoeukaryotes and picocyanobacteria. There is not that much know of the group in this region of the world. This means that very closely related picoplankton will react different to environmental changes. In this study I investigated how two photosynthetic picoplankton strains (Syn5 and Syn7) reacted to different light spectrums and nitrogen sources in combination with the aim to know their niche in the ocean. This was investigated in the lab with experimental flasks covered with colored cellophane papers and prepped with two different nitrogen sources (nitrate and ammonia). The isolates were also determined genetically by sequencing of a fragment of the 16S rRNA. White light showed better growth compared to red and green light for Syn7. There were no interaction effects found or effects from nutrients solely. The isolates 16S rRNA gene showed high similarity to plastid sequences of Chlorophyta and had high identity with previously reported sequences from the Baltic Sea. Different responses indicated that the two isolates can be adapted to different ecological niches, but more investigation is needed.