Cell counts and POC/PON content of P.antartica for the 4 different treatments were determined at the beginning and at the end of the experiment. The cell density and size were determined using a Beckman MultisizerTM 3 Coulter Counter® with a 100 μm aperture. For the POC/PON, 250 mL of water were filtered onto pre-combusted glass-fiber filters (15h, 500 ̊C, GF/F, ~0.6 μm, 25 mm, Whatman, Wisconsin, USA) and stored at -20°C in pre-combusted glass petri dishes. Prior to analysis with an Euro Elemental Analyzer 3000 CHNS-O (HEKAtech GmbH), the filters were dried for > 12h at 60 °C and then acidified with 200 μL of 0.2N HCL to remove inorganic carbon and dried a second time. Contents of POC and PON were corrected for blank measurements and normalized to filtered volume and cell densities to yield cellular quotas.