Changes in plankton and fish larvae communities across hydrographic fronts off West Greenland

The variability in plankton community structure was studied in Disko Bay and across important fishing banks off the west coast of Greenland. The primary goal of the study was to investigate possible linkages between hydrographical processes and plankton structures, hypothesizing that hydrographic fronts would be present in the area, and that these to a large extent determine plankton distribution, composition and productivity. We sampled along four cross-shelf transects, one covering Disko Bay and Disko Bank, while the other three covered Store Hellefiske Bank, Lille Hellefiske Bank and Sukkertop Bank. The hydrography was examined by CTD profiling, the phytoplankton by fluorescence profiling and water bottle sampling, while mesozooplankton and ichthyoplankton were sampled by vertical or oblique net hauls, respectively. We observed distinct along-shelf flowing currents in the area (e.g. the West Greenland Current, the Polar Current and the Irminger Current), and the physical characteristics indicated frontogenesis at the shelf slope, in regions of 80–100 m water depth. Phytoplankton and ichthyoplankton showed a cross-shelf structuring with apparent linkages to frontal characteristics, while a more diverse pattern was observed for the mesozooplankton which were dominated by Calanus finmarchicus, Calanus glacialis and Calanus hyperboreus. The relationship between hydrographic characteristics and plankton distribution differed among species, and apparently specific plankton communities were established in different areas of the shelf. For example the larvae of Boreogadus saida, Ammodytes sp., Reinhardtius hippoglossoides and Stichaeus punctatus differed markedly in distributional characteristics. In addition to the cross-shelf structuring, marked differences in species composition and total plankton abundance were observed in the along-shelf (north–south) direction. The latitudinal differences in the unicellular plankton communities are interpreted largely within a seasonal successional framework (i.e. an early dominance of diatoms followed by increasing importance of smaller unicellular plankton), while the ichthyo- and zooplankton communities also differed by the respective dominance of species with polar versus temperate origin. Our findings suggest that the flow of major currents and the establishment of hydrographical fronts are of primary importance to the plankton communities in the West Greenland shelf area, influencing the early life of fish and the recruitment to the important fisheries resources.