AME 16:217-232 (1999)  -  doi:10.3354/ame016217

Plankton community structure and carbon cycling on the western coast of Greenland during the stratified summer situation. II. Heterotrophic dinoflagellates and ciliates

Henrik Levinsen1,*, Torkel Gissel Nielsen1, Benni Winding Hansen2

1National Environmental Research Institute, Department of Marine Ecology and Microbiology, Frederiksborgvej 399, PO Box 358, DK-4000 Roskilde, Denmark
2Roskilde University, Department of Life Sciences and Chemistry, PO Box 260, DK-4000 Roskilde, Denmark

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

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