Optical methods in zooplankton studies – how efficient is LOKI (Lightframe On-sight Key species Investigation) in analyzing Arctic zooplankton communities?

• Main Authors: Hildebrandt, Nicole, Henke, Theresa, Niehoff, Barbara
• Format: Conference Object
• Language: unknown
• Published: 2017
• Subjects: Arctic; Zooplankton; Copepods
• Online Access: https://epic.awi.de/id/eprint/44056/; https://hdl.handle.net/10013/epic.50567

Optical methods are increasingly important in zooplankton studies. They allow to cover wide spatial ranges and to study the distribution of dominant taxa in greater detail than with classical net tows. The Lightframe On-sight Key species Investigation system (LOKI) is a plankton recorder that provides high-resolution photographs (4 megapixel) of mesozooplankton organisms and particles taken directly in the water column during vertical hauls from 1000 m to the surface. A build-in image analysis automatically recognizes objects in the pictures and saves the respective vignettes for later analyses. In addition to the camera system, the LOKI carries sensors for measuring depth, salinity, temperature, oxygen concentration and fluorescence. This allows to study the small-scale zooplankton distribution patterns in relation to environmental conditions. In order to evaluate how efficient LOKI is in analysing Arctic zooplankton communities, we attached a net to the outflow of the camera system. This allows to evaluate how many of the individuals passing by are detected by the camera. The comparability of the results with traditional multi-net hauls is another criterion for the reliability and performance of the LOKI. Hence, we conducted parallel sampling of zooplankton with LOKI and multi-net hauls on the same stations during various expeditions with RV Polarstern. Both gears were equipped with nets of 150 μm mesh size and towed vertically with 0.5 m sec-1 from 1000 m depth to the surface. Results indicate that the abundances of dominant large taxa (Calanus, Metridia, ostracods) determined by LOKI mirror their abundance in net samples, whereas small, fragile copepods (Oithona) as well as fast swimming predators (chaetognaths, amphipods) are under-sampled by LOKI. These results will be discussed in the view of suitability of the LOKI system for studies on zooplankton distribution and biodiversity. Summarizing the hitherto experience with the LOKI, we will also present suggested improvements in data analysis and workflow.