EN
Nanoflagellates are important bacterivores, but their role is often underestimated because forms capable of phagotrophy and containing chlorophyll (mixotrophs) are excluded from analyses. Research conducted in the coastal zone of the Gdańsk Basin (Baltic Sea) revealed seasonal changes in the relationship between the biomasses of small (1–8 μm) nanoflagellates with (NFChl+) and without chlorophyll (NFChl–). Three distinct patterns were distinguished: (i) spring, when the biomass of NFChl+ was lower than that of NFChl–, (ii) summer and autumn, when NFChl+ were dominant (about 90%), and (iii) late autumn and winter, when the prevalence of NFChl+ was lower (71–79%). Additional studies showed the existence of spatial differences in the composition of the nanoflagellate community. These spatial differences were not shaped by freshwater input. The possible importance of mixotrophic forms in the Gdańsk Basin is discussed.