Contrasting resistance of prokaryotic plankton biomass and community composition to experimental nutrient inputs in a coastal upwelling system (NW Spain).

Increasing nutrient inputs driven by global environmental pressures may lead to changes in prokaryotic plankton biomass and community composition in coastal environments. Nutrient addition experiments (inorganic, organic, and mixed) were performed at the continental shelf outside the Ría de Vigo, in spring, summer and autumn 2014, and the results contrasted with those from similar previous experiments carried out inside the ría in 2013. The mixed nutrient additions caused the greatest changes in community composition, mostly consisting of blooms of Vibrionales. Inorganic nutrients yielded increased proportions of Oceanospirillales and Alteromonadales. Euclidean distances among samples were used to estimate compositional resistance to disturbances derived from nutrient additions. Changes in prokaryotic biomass were used as an indicator of biomass resistance. Generally, prokaryotic communities were more resistant to inorganic than organic nutrient additions. Communities sampled inside the ría, presumably exposed to greater perturbations, showed milder variability in the non-amended control than those from outside the ría. By contrast, shelf communities, with higher ambient organic matter concentrations, were more resistant to organic and mixed nutrient additions than those from the ría. Our data suggest that the perturbation history is related to the resistance of microbial communities to changes in nutrient inputs into the coastal ocean. [ABSTRACT FROM AUTHOR]