PLANKTON COMMUNITIES IN TWO FJORDS OF WEST SPITSBERGEN

Abstract

Samples of phyto-, bacterio- and zooplankton were collected from two small fjords of West Spitsbergen Island during the spring and summer seasons of 2007–2010. The phytoplankton level was generally low throughout the study period; total algal abundances being somewhat higher in spring compared to the summer, with the exception of 2007. Although the species composition of the dominant algal plankton groups varied among years, Dinophyta and Flagellata always contributed the most. Total bacterioplankton abundance in the upper water layer of both fjords varied between 0.45 and 3.5*106 cells/ ml. Total bacterioplankton abundance and biomass in Gren-Fjord and Billefjord imply their mesotrophic state. The abundances peaked in spring, exceeding the summer values 1.5- to 3‑fold in different years. The relative abundances of different morphological types of bacterial cells in Gren-Fjord during sampling periods of 2007, 2009 and 2010 were similar; and the cocci morphological type dominated. In 2008, however, the bacterioplankton consisted of nearly equal abundances of rods and cocci in both fjords. Bacterioplankton concentrations in the top 30‑m water layer were 2–2.5 higher compared to near-bottom layers. The zooplankton species diversity was dominated by widespread Arctic and ArctoBoreal species. While Calanus finmarchicus (Gunner 1765), Oithona similis (Claus 1866), nauplii and veligers of bivalves contributed the most in abundance, the greatest contribution to biomass was made by Calanus finmarchicus and Sagitta е legans (Verrill 1873). Being an important control of zooplankton development, hydrological conditions strongly influence the spatial distribution of the community.