ABSTRACT: The structure and ecological role of protozooplankton (ciliates and heterotrophic dinoflagellates) were studied in Disko Bay, West Greenland, from mid-July to mid-September 1994. Heterotrophic dinoflagellates dominated the protozooplankton biomass. When diatoms formed subsurface blooms, heterotrophic dinoflagellates averaged 70% of the integrated protozooplankton biomass. After the diatoms declined, large heterotrophic dinoflagellates became less abundant. Ciliates followed the same vertical distribution as heterotrophic dinoflagellates. However, in contrast to heterotrophic dinoflagellates, maximum ciliate biomasses developed in surface water after the diatom blooms, when the large copepods (Calanus spp.) migrated to the deeper water. Mixotrophic oligotrich ciliates, mainly Laboea strobila, contributed on average 20% to the integrated ciliate biomass. Growth experiments revealed similar specific maximum growth rates for ciliates and heterotrophic dinoflagellates. Maximum growth rates were allometrically related to cell volume. Ciliates and heterotrophic dinoflagellates appear to be key organisms in the cycling of organic matter in this Arctic pelagic ecosystem.

KEY WORDS: Arctic pelagic food web · Protozooplankton structure · Ciliates · Heterotrophic dinoflagellates

Published in AME Vol. 16, No. 3 (1999) on February 24
ISSN: 0948-3055. Copyright © Inter-Research, Oldendorf/Luhe, 1999