Cell counts and cell specific chlorophyll autofluorescence were mea- sured using a BD Accuri C6 flow cytometer. Culture samples were dilute ed (100 LL culture in 900 uL medium) and passed through 30 Hm filters to remove debris. Flow cytometry was carried out at a flow rate of 35 uL min and a core size of 16 Hm. Phaeodactylum cells were quanti fied after gating from forward scatter and relative fluorescence emission (excitation at 488 nm, emission detection at 670 nm).