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Environmental DNA metabarcoding reveals seasonal and spatial variation in the vertebrate fauna of Ilulissat Icefjord, Greenland

Sascha Schiøtt*, Mads Reinholdt Jensen, Eva Egelyng Sigsgaard, Peter Rask Møller, Marcelo de Paula Avila, Philip Francis Thomsen, Søren Rysgaard

*Corresponding author:

ABSTRACT: Ilulissat Icefjord in Greenland is experiencing the effects of climate change, with the Sermeq Kujalleq glacier now being one of the fastest moving and most productive ice streams in Greenland. This is most likely affecting the distribution of species in the fjord including species of importance for local fisheries, but due to heavy ice conditions, few studies on environmental and ecological conditions have been made. However, new techniques such as environmental DNA (eDNA) metabarcoding make it possible to gain deeper insight into the fjord system. Here, we combine local ecological knowledge with data on hydrographic conditions (Conductivity, Temperature, Depth: CTD), stable isotopes (δ 18O), and eDNA metabarcoding to investigate the spatial and seasonal distribution of marine fish and mammals inside Ilulissat Icefjord. Our eDNA results support the local observations that Arctic char migrate to the southern fjord branch during the summer, that harp seals forage in large herds in the fjord system, that polar cod is the dominant prey fish in the area, and that Greenland shark most likely does not reside in the fjord system. Lower predation pressure in the Icefjord, due to the absence of the Greenland shark and polar bears, as well as limited fishing/hunting activities in the fjord, are presumed to be one of the reasons why ringed seals and Greenland halibut are known to be larger in the Icefjord. Furthermore, our results indicate that in summer, the southern branch of the fjord system has a more diverse community of vertebrates, but also different water masses compared to the northern branch and main fjord, which indicate a time lag between inflows to the different branches of the fjord system. Our approach highlights the value of combining local ecological knowledge with scientific research and represents a potential starting point for monitoring biological responses in Ilulissat Icefjord associated with climate-induced changes.