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Seasonal patterns in composition and biomass of autotrophic and heterotrophic nano- and microplankton communities on the north Norwegian shelf
Verity, P.G.; Wassmann, P.; Ratkova, T.N.; Andreassen, I.; Nordby, E. (1999). Seasonal patterns in composition and biomass of autotrophic and heterotrophic nano- and microplankton communities on the north Norwegian shelf. Sarsia 84: 265-277
In: Sarsia. University of Bergen. Universitetsforlaget: Bergen. ISSN 0036-4827, more
Peer reviewed article  

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Keyword
    Marine

Authors  Top 
  • Verity, P.G.
  • Wassmann, P.
  • Ratkova, T.N.
  • Andreassen, I.
  • Nordby, E.

Abstract
    From monthly transects on the shelf off northern Norway, data describe the size, abundance, and biomass of photosynthetic nano-and picoplankton, heterotrophic (aplastidic) nanoplankton, and ciliates. Samples were analyzed using a state-of-the-art color imaging system. The numerically dominant phytoplankton were pico-and nanoplankton. Highest biomasses occurred in summer, and in- creased earlier in the year and attained higher values in inshore stations compared to offshore sta- tions.Mean cell sizes were small,2-5 µm diameter nanoplankton and 1 µm eucaryotic picoplankton; cyanobacteria were comparatively unimportant contributors to biomass. The dominant herbivores appeared to be heterotrophic flagellates, which were generally similar in size, concentration, and biomass to the phototrophic forms. Their temporal and spatial distribution mimicked their putative prey, except that they often occurred in abundance deeper than the photosynthetic nanoplankton. Oligotrich ciliates were also abundant. The ratio of photosynthetic: heterotrophic plankton (P:H) biomass exhibited spatial and temporal trends. P:H in surface waters was low in March (<0.5), increased to maxima (2-3)in June-July, and decreased again during late summer and into October (0.4-0.6).Contrary to expectations, small-celled auto-and heterotrophs apparently dominated nutrient uptake, remineralization, and likely reduced vertical fluxes of microplankton-derived organic matter from the euphotic zone of the north Norwegian shelf. It is suggested that the significance of small cells was exacerbated by significant grazing of large phytoplankton and protozoans by meso-and macrozooplankton.

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