| Abstract: | The Arctic is warming at least four times faster than the global average, as a result of anthropogenic climate change. Sea and air temperatures are rising, and perennial sea ice coverage has declined over the last four decades, with ice-free summers predicted to occur before 2050. Furthermore, in the Arctic gateway, Fram Strait, an increasing influence of warm Atlantic water is driving the ‘Atlant... The Arctic is warming at least four times faster than the global average, as a result of anthropogenic climate change. Sea and air temperatures are rising, and perennial sea ice coverage has declined over the last four decades, with ice-free summers predicted to occur before 2050. Furthermore, in the Arctic gateway, Fram Strait, an increasing influence of warm Atlantic water is driving the ‘Atlantification’ of both environmental and biological processes. These changes affect habitat and resource availability for marine species in the region, causing shifts in species distributions and assemblages. There has been an intensification in research targeting the impacts of these changes over the last decades, however, important gaps in baseline knowledge of the current state of Arctic marine biodiversity still remain. The development of environmental DNA (eDNA) metabarcoding techniques has given rise to cost-effective and non-invasive methods for biodiversity assessments. One major advantage of eDNA is that it has the potential to detect delicate or elusive taxa that are typically overlooked or damaged by traditional net sampling, such as gelatinous zooplankton (GZP). This highly diverse group plays major roles across Arctic marine ecosystems. However, gaps in basic ecological data persist, including information on species assemblages and distribution. Thus, the overarching aim of this thesis was to apply eDNA metabarcoding to increase our knowledge of Arctic marine biodiversity, with a focus on GZP ecology.
Environmental DNA signals elucidated well-known vertical structuring of pelagic diversity and community composition in the open ocean (Chapter Two) and in the marginal ice zone (Chapter Three) of Fram Strait. Distinct community assemblages were linked to environmental conditions, which represented different water masses (Chapter Two) and different sea ice and meltwater dynamics (Chapter Three). Finally, significant structuring in community composition was revealed across the inner section of a Svalbard fjord (Chapter Four), based on seawater- and sediment-derived eDNA. These findings demonstrate that eDNA metabarcoding is a valuable tool for investigating the spatial patterns and abiotic drivers of marine biodiversity in the Arctic. It also proved to be a sensitive and accurate method for investigating biodiversity across different spatial scales, habitats, seasons and environmental conditions. It was applied across a large area of the open ocean in Fram Strait during summer, in a sampling scheme that encompassed depths from surface waters down to the bathypelagic (Chapter Two). It was also used to detect fine-scale patterns in the upper meters of the sub-ice water column in the marginal ice zone, during the late summer (Chapter Three). Lastly, it was implemented during the polar night period, in the central section of a semi-enclosed fjord system with high levels of glacier input and water turbidity (Chapter Four).
Additionally, this thesis was able to demonstrate that eDNA metabarcoding is a valuable method for investigating the diversity of GZP in the Arctic Ocean. Comparisons between eDNA and non-DNA-based survey methods (Chapters Two and Four) showed that eDNA recovered the highest numbers of species. It was also evident that each technique had inherent biases, with different GZP communities detected depending on the survey method used. Thus, we were able to confirm that eDNA greatly improves our repertoire for sampling GZP in the Arctic, but a combination of sampling methods should be employed to gain a more accurate picture of the diversity present. Finally, multi-marker analyses were applied (Chapters Three and Five) to further investigate the accuracy of two commonly used universal metabarcoding markers and their associated primers for amplifying common Arctic GZP taxa. The COI gene showed higher taxonomic resolution (e.g., species-level) but was affected by primer mismatches for some groups. The 18S gene was able to amplify more GZP groups, but genus and species-level assignments were not accurate. Therefore, it was evident that both are useful for investigating GZP diversity, but which one to prioritize should be determined by the research question at hand. Finally, it was evident that gaps in reference databases persist for both genes and that filling these with GZP samples from the Arctic should be a priority for future research.
Overall, the research presented in this thesis supports the use of eDNA metabarcoding as a non-invasive and sensitive method for improving our understanding of Arctic marine biodiversity. It shows the utility of eDNA metabarcoding to go beyond presence data and to investigate abiotic drivers of eukaryotic biodiversity in different marine habitats and conditions. Moreover, it highlights the benefits of incorporating eDNA methods into GZP research to better understand how this important, yet understudied group will be affected by ongoing climate change in the Arctic. Finally, this thesis contributes valuable baseline data to our current understanding of marine eukaryotic biodiversity in the Atlantic sector of the Arctic. |
