Prokaryotic and eukaryotic microbial community responses to N and P nutrient addition in oligotrophic Mediterranean coastal waters: Novel insights from DNA metabarcoding and network analysis

The effects of the abrupt input of high quantities of dissolved inorganic nitrogen and phosphorus on prokaryotic and eukaryotic microbial plankton were investigated in an attempt to simulate the nutrient disturbances caused by eutrophication and climate change. Two nutrient levels were created through the addition of different quantities of dissolved nutrients in a mesocosm experiment. During the developed blooms, compositional differences were found within bacteria and microbial eukaryotes, and communities progressed towards species of faster metabolisms. Regarding the different nutrient concentrations, different microbial species were associated with each nutrient treatment and community changes spanned from the phylum to the operational taxonomic unit (OTU) level. Network analyses revealed important differences in the biotic connections developed: more competitive relationships were established in the more intense nutrient disturbance and networks of contrasting complexity were formed around species of different ecological strategies. This work highlights that sudden disturbances in water column chemistry lead to the development of entirely different microbial food webs with distinct ecological characteristics. •Bacterial and microbial eukaryotic communities changed after addition of high quantities of dissolved inorganic N and P.•Composition changes were obvious at the phylum level; Actinobacteria, Chlorophytes, Cryptophytes differentiated treatments.•Succession of plankton populations was similar under different nutrient conditions.•Few differentiations were found in the succession of the micro-eukaryotes: Bacillariophyta, Cilliophora and Dinoflagellata.•Different nutrient quantities caused changes in the ecological connections among OTUs.•Low nutrient addition resulted in more positive relationships between same trophic groups; high addition in negative ones.