For the comparison of the share of biomass within the microbial community samples were collected on monthly basis from the Adriatic Sea (N = 110) from one coastal (ST103) and one open sea (CA009) site during 2010. Seawater samples from the Adriatic Sea sites and offshore site in the English Channel were collected by Niskin bottles through vertical profile. At four shore sites from the English Channel samples were collected manually from the surface. All samples were fixed with formaldehyde (2% final concentration), kept in the dark at 4 ºC and analyzed within two weeks. For epifluorescence microscopy (EM) preserved samples were stained with 4'-6-diamidino-2-phenylindole (DAPI) (1 μg.
