Seasonal patterns in composition and biomass of autotrophic and heterotrophic nano- and microplankton communities on the north Norwegian shelf

Abstract

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 pica- and nanoplankton. Highest biomasses occurred in summer, and increased earlier in the year and attained higher values in inshore stations compared to offshore stations. Mean cell sizes were small, 2-5μ.m diameter nanoplankton and 1μm 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 r...