Using the optical plankton recorder LOKI (Lightframe On-sight Key species Investigations) to elucidate high-resolution vertical distribution patterns of Arctic zooplankton species in Fram Strait

The plankton recorder LOKI provides high-resolution pictures, continuously taken by a 4 Megapixel camera during vertical hauls from 1000 depth to the surface. Linked to each picture, hydrographical parameters are being recorded, e.g. salinity, temperature, oxygen concentration and fluorescence. This allows to exactly identifying distribution patterns in relation to environmental conditions. In order to analyse the community composition, abundance and depth distribution of the species in the Fram Strait, we have conducted two hauls during a RV Polarstern cruise in July/August 2015 (PS93.2) to the deep-sea observatory “Hausgarten” of the Alfred-Wegener-Institute, Germany. We sampled the most northern (79°56’35” N, 3°11’45” E) and the most southern station (78°35’97” N, 5°4”11” E) of the “Hausgarten” monitoring stations. The two stations were similar with regard to zooplankton community composition. Copepods, among which Calanus, Oncaea and Microcalanus were the most frequent genera, dominated with a contribution of more than 80%. Calanus reached the highest abundances in surface layers ( 300m. Abundances at the northern station were twice as high as at the southern station. Mean weighted depths of the dominant taxa were significantly deeper at the northern than at the southern station, which corresponded to the deeper location of the Return Atlantic Intermediate Water.