The aim of t h~s study was to quantify zooplankton feeding interactions and copepod reproduction dunng blooms of dlatoms and flagellates (lncludlng E m~l l a n~a huxleyl) In fertilised mesocosms A number of mlcrozooplankton grazlng (dilution senes), copepod f e e d~n g (bottle ~ncubation) and egg productlon experiments were performed during a 4 \vk summer penod Mlcrozooplankton (malnly ciliates) peaked dunng an initial bloom d o m~n a t e d by the diatom Skeletonema costatum and flagellates 210 pm w h~c h apparently became grazer-controlled Mauimum grazing rates were 1 5 to 1 8 d.' for diatoms, the calcifying haptophyte Emlllan~a huxleyl and flagellates 2 to 10 pm, and 65 to 80% of the average standing stock of these algae were removed dally Dunng a subsequent bloom of E h u x l e y~ the m~crozooplankton composition changed and ~t s biomass decreased to <25 % and the daily turnover of dlatoms and E huxleyl fell to ca 50% In contrast to other algae E huxleyl spec~fic growth was never surpassed by microzooplankton grazlng The copepod C finn~archlcus (CV and CV1 females) preferred cihates 230 pm, but ciliates <30 pm, dlatoms and rotlfers were also occas~onally preyed upon at h~g h rates E h u x l e y~ was barely Ingested at low concentrations (0 4 to 6 X 105 cells I-') but was cleared at 106 m1 lnd -' d ' at peak concentrations (1 2 X 107 cells I-') It then made up 74 % of total carbon Ingestion Although copepod lngest~on rates were slmilar dunng blooms of diatoms and E huxleyl, egg productlon rates were s~gnlficantly higher dunng blooms of the latter, and mesozooplankton biomass increased 3 tlmes more In mesocosms dominated by E huxleyl compared to mesocosms w~t h dlatom blooms at slmllar algal blomass Impact by copepods on the phytoplankton development was m a n l y induced lndlrectly by selective predation on the m~crozooplankton A method to correct copepod feeding rate measurements for errors d u e to loss of n~~crozooplankton grazing In the ~n c u b a t~o n bottles IS presented