Abstract
Climate warming is rapidly altering marine ecosystems towards a more temperate state on the European side of the Arctic. However, this “Atlantification” has rarely been confirmed, as long-term datasets on Arctic marine organisms are scarce. We present a 19-year time series (1982–2016) of diet samples from black-legged kittiwakes as an indicator of the changes in a high Arctic marine ecosystem (Kongsfjorden, Svalbard). Our results highlight a shift from Arctic prey dominance until 2006 to a more mixed diet with high contribution of Atlantic fishes. Capelin, an Atlantic species, dominated the diet composition in 2007, marking a shift in the food web. The occurrence of polar cod, a key Arctic fish species, positively correlated with sea ice index, whereas Atlantic species demonstrated the opposite correlation indicating that the diet shift was likely connected with recent climate warming. Kittiwakes, which gather available fish and zooplankton near the sea surface to feed their chicks, can act as messengers of ecosystem change. Changes in their diet reveal that the Kongsfjord system has drifted in an Atlantic direction over the last decade.
Highlights
Climate change in the Arctic is a model projection but an ongoing process[1,2]
Arctic species contributed significantly more than Atlantic species to the wet weight of regurgitates in 1997–1998, 2004–2006, and 2011–2012 (Fig. 3, see Extended Data Table 2 for model statistics), whereas Atlantic species contributed more than Arctic species in 2007
Decreasing contribution of Arctic species concomitant with the increase in Atlantic fishes in kittiwake diet samples from Kongsfjorden are likely connected with recent climate warming − driven by increased advection from West Spitsbergen Current and dramatic decrease in marginal sea ice extent around Svalbard[4,29,30]
Summary
Climate change in the Arctic is a model projection but an ongoing process[1,2]. The European side of the Arctic, including the northern Barents Sea and Svalbard archipelago (Fig. 1a), has gradually experienced less sea ice and warmer water temperatures during the last four decades[3,4,5] Such changes in physical drivers influence species distributions: Arctic species retract northwards following the retreating marginal ice zone, while abundances of boreal and Atlantic species are expected to increase in the warmer sea-ice-free habitat[6,7,8]. This “borealization” of the Arctic[6], or the “Atlantification” of the European Arctic, will affect the food web structure by altering the community composition of lower and middle trophic levels[6,7,9]. We used a unique long-term time series of diet samples from kittiwakes breeding around inner Kongsfjorden to test whether the ecosystem has changed in an Atlantic direction, with concurrent food-web changes in the lower part of the marine ecosystem
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