Vertical distributions of zooplankton using the Video Plankton Recorder in two high-latitude fjords. “A case study on diel migration in Billefjorden, Svalbard, and seasonal migration in Porsangerfjord, northern Norway”

Abstract

Zooplankton is the link between primary producers and higher trophic levels, so it is of vital importance for the food chain. The strong seasonality in the Arctic affects the vertical distribution of zooplankton in the water column. Predators can also affect the vertical distributions of their prey in the water column due to avoidance adaptations. The importance of these differences between prey and predator vertical distributions is the main point of interest in this study. The present study is an attempt to gain more knowledge about how the vertical distribution and interactions between prey and predator zooplankton affect the structure/their disposition throughout the water column. It is important to know the interactions and vulnerability of the species, and how they adapted to survive in this special environment. The study took place in two different arctic fjords, where diel and seasonal migrations were studied. The diel vertical migration (DVM) of prey related to predators was studied, using a Multi Plankton Sampler (MPS), MIK nets, trawl nets and the video Plankton Recorder (VPR) in Billefjorden, Svalbard. The seasonal vertical migration (SVM) was studied along different sampling stations at Porsangerfjord, Northern Norway. The zooplankton community of Porsangerfjord has not been deeply studied. This study will try to cover the lack of information in this area. DVM was observed for more vulnerable prey species and SVM was observed for all the species. Migration to the surface was related to the phytoplankton bloom for all the species. Also, differences in distributions between predator – prey and small – large copepods were observed some of the months. In summer and fall, small and large copepods have different vertical distributions and predators affect on the vertical distribution of their prey. Visual predators can be in high abundance in fjords in Norway and further analysis comparing acoustic data from echo sounders with data from VPR will give a better overview on the predator – prey interactions and migrations.