Microbial processes in a high-latitude fjord (Kongsfjorden, Svalbard): II. Ciliates and dinoflagellates |
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Authors: | Lena Seuthe Kriss Rokkan Iversen Fanny Narcy |
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Institution: | (1) Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics, University of Troms?, 9037 Troms?, Norway;(2) Norwegian Polar Institute, 9296 Troms?, Norway;(3) Laboratoire d’Oc?anographie de Villefranche, UPMC, Univ Paris 06, UMR 7093, 06234 Villefranche-sur-mer, France;(4) Laboratoire d’Oc?anographie de Villefranche, CNRS, UMR 7093, 06234 Villefranche-sur-mer, France |
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Abstract: | The composition and ecological role of ciliates and dinoflagellates were investigated at one station in Kongsfjorden, Svalbard,
during six consecutive field campaigns between March and December 2006. Total ciliate and dinoflagellate abundance mirrored
the seasonal progression of phytoplankton, peaking with 5.8 × 104 cells l−1 in April at an average chlorophyll a concentration of 10 μg l−1. Dinoflagellates were more abundant than ciliates, dominated by small athecates. Among ciliates, aloricate oligotrichs dominated
the assemblage. A large fraction (>60%) of ciliates and dinoflagellates contained chloroplasts in spring and summer. The biomass
of the purely heterotrophic fraction of the ciliate and dinoflagellate community (protozooplankton) was with 14 μg C l−1 highest in conjunction with the phytoplankton spring bloom in April. Growth experiments revealed similar specific growth
rates for heterotrophic ciliates and dinoflagellates (<0–0.8 d−1). Food availability may have controlled the protozooplankton assemblage in winter, while copepods may have exerted a strong
control during the post-bloom period. Calculations of the potential grazing rates of the protozooplankton indicated its ability
to control or heavily impact the phytoplankton stocks at most times. The results show that ciliates and dinoflagellates were
an important component of the pelagic food web in Kongsfjorden and need to be taken into account when discussing the fate
of phytoplankton and biogeochemical cycling in Arctic marine ecosystems. |
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