Stauffer, Julian B. (2022) Using eDNA and in situ observations to study Arctic cephalopod distribution and diversity. (Master thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 64 pp.

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Abstract

Cephalopods are key players in marine foodwebs, connecting trophic levels as predators of fish, crustaceans, and other cephalopods and as prey for various oceanic consumers. Knowledge about cephalopods is still limited, in particular for species inhabiting regions that are hard to access (e.g., deep sea, polar regions) or regions without cephalopod fisheries. Cephalopod populations have been proliferating during the last decades as a result of climate change and depletion of fish populations. The Arctic Ocean ecosystem is subject to one of the highest rates of global change. The Arctic Ocean is increasingly influenced by Atlantic water masses that expand northwards (Atlantification), changing the physical environment of its inhabitants. As such, it is expected that diversity and distribution alterations are occurring in marine Arctic nekton communities as observed already for some fish and plankton communities. To assess the biological impacts of Atlantification, this thesis aimed to establish diversity and distribution baseline data of Arctic cephalopods. Towards this aim, we used a combined approach of environmental DNA (eDNA) metabarcoding using a universal cephalopod primer pair targeting the 18S rRNA gene and video analysis. Samples for the eDNA analysis were taken in 2019 during the PS121 cruise to the HAUSGARTEN observatory located in the Fram Strait. Four stations were sampled in biological quadruplicates at 8 depths from 50 m to 2250 or 2534 m, resulting in 128 samples. Data on cephalopod taxa was extracted from videos obtained during three cruises. Two cruises used the towed camera PELAGIOS during horizontal video transects in the Fram Strait (approx. 20-2500 m). Additionally, video was collected during the ascent and descent of the remotely operated vehicle (ROV) used during the cruise SO276, which steamed from the Norwegian Basin to the Porcupine Abyssal Plain in the Northern Atlantic. Despite serious contamination issues, the eDNA analysis showed that the 18S universal cephalopod primer can amplify and detect the two most abundant Arctic cephalopod species Gonatus fabricii and Rossia palpebrosa. We encountered 42 individual cephalopods during the video transects, including Gonatus sp., Cirroteuthis muelleri, and Mastigoteuthidae. The video footage allowed to document different cephalopod behaviour like inking by Gonatus and motionless, upside-down drifting by cirrates. To optimize the cephalopod eDNA pipeline, a new universal cephalopod primer was developed that targets the 28S rRNA gene. This novel primer was able to amplify cephalopod DNA extracted from tissues and could identify 16 out of 46 cephalopod species at least to genus level. The 28S primer could identify species that could not be detected by the 18S universal primer used here. This study showed that the combined approach of eDNA and video analysis is a promising tool to study distribution and diversity of Arctic cephalopods. Unfortunately, contamination during the eDNA pipeline prevented statements about exact species diversity and distribution. The 28S rRNA gene proved to be useful for the development of a universal cephalopod primer, but the primer should be modified for eDNA metabarcoding application.

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