Phytoplankton size structure and environmental forcing within the euphotic zone in Southern Adriatic-Ionian coastal area

Here, we analysed the variation of size–abundance distributions of marine nano- and micro-phytoplankton guilds in relation to main environmental forcing factors and taxonomic composition. The study was carried out in the Southern Adriatic–Ionian Region and was based on physical, chemical and biological data collected during four cruises at 21 stations on seven transects. Biological data included density, individual cell size and species composition of nanoand micro-phytoplankton guilds and total and size-fractionated biomass of the entire phytoplankton community. We used canonical correspondence analysis to relate variation in nano- and micro-phytoplankton size–abundance distributions to variation of spatial, abiotic and biotic environmental forcing factors. Results showed that environmental forcing factors explained up to 75% of the size–abundance distribution variation in the study area. Variations in size–abundance distributions of the nano- and micro-phytoplankton guilds were relatively independent of taxonomic composition. Therefore, the obtained results suggested a relevant role of individual body size as an organizing factor of phytoplankton guilds.