Calculation procedure =We calculate the phytoplankton standing stock from which the non-uniform grazing begins, with Eq. (12) =We then assess phytoplankton production according(17). The time from to to t in this equation represents the period of non-uniform grazing equals the period of 8 night hours: =This value represents the diurnal production, providing that only non-uniform grazing on the main phytoplankton mass occurs by migratory ind of Calanus helgolandicus, and providing that only living cells are grazed As at dawn of subsequent days