Consequences of Atlantification on a Zooplanktivorous Arctic Seabird

Global warming, combined with an increasing influence of Atlantic Waters in the European Arctic, are causing a so-called Atlantification of the Arctic. This phenomenon is affecting the plankton biomass and communities with potential consequences for the upper trophic levels. Using long-term data (2005-2020) from a high Arctic zooplanktivorous seabird, the little auk (Alle alle), we tested the hypothesis that the Atlantification affects its diet, body condition and demography. We based our study on data collected in three fjords in West Spitsbergen, Svalbard, characterized by distinct oceanographic conditions. In all three fjords, we found a positive relationship between the inflow of Atlantic Waters and the proportion of Atlantic prey, notably of the copepod Calanus finmarchicus, in the little auk chick diet. A high proportion of Atlantic prey was negatively associated with adult body mass (though the effect size was small) and with chick survival (only in one fjord where chick survival until 21 days was available). We also found a negative and marginally significant effect of the average proportion of Atlantic prey in the chick diet on chick growth rate (data were available for one fjord only). Our results suggest that there are fitness costs for the little auk associated with the Atlantification of West Spitsbergen fjords. These costs seem especially pronounced during the late phase of the chick rearing period, when the energetic needs of the chicks are the highest. Consequently, even if little auks can partly adapt their foraging behaviour to changing environmental conditions, they are negatively affected by the ongoing changes in the Arctic marine ecosystems. These results stress the importance of long-term monitoring data in the Arctic to improve our understanding of the ongoing Atlantification and highlight the relevance of using seabirds as indicators of environmental change.publishedVersio

Consequences of Atlantification on a Zooplanktivorous Arctic Seabird

Global warming, combined with an increasing influence of Atlantic Waters in the European Arctic, are causing a so-called Atlantification of the Arctic. This phenomenon is affecting the plankton biomass and communities with potential consequences for the upper trophic levels. Using long-term data (2005-2020) from a high Arctic zooplanktivorous seabird, the little auk (Alle alle), we tested the hypothesis that the Atlantification affects its diet, body condition and demography. We based our study on data collected in three fjords in West Spitsbergen, Svalbard, characterized by distinct oceanographic conditions. In all three fjords, we found a positive relationship between the inflow of Atlantic Waters and the proportion of Atlantic prey, notably of the copepod Calanus finmarchicus, in the little auk chick diet. A high proportion of Atlantic prey was negatively associated with adult body mass (though the effect size was small) and with chick survival (only in one fjord where chick survival until 21 days was available). We also found a negative and marginally significant effect of the average proportion of Atlantic prey in the chick diet on chick growth rate (data were available for one fjord only). Our results suggest that there are fitness costs for the little auk associated with the Atlantification of West Spitsbergen fjords. These costs seem especially pronounced during the late phase of the chick rearing period, when the energetic needs of the chicks are the highest. Consequently, even if little auks can partly adapt their foraging behaviour to changing environmental conditions, they are negatively affected by the ongoing changes in the Arctic marine ecosystems. These results stress the importance of long-term monitoring data in the Arctic to improve our understanding of the ongoing Atlantification and highlight the relevance of using seabirds as indicators of environmental change.publishedVersio

Foraging, reproduction and survival of the zooplanktivorous seabird Little Auk (Alle alle) in the Arctic in relation to climatic and environmental variability

The ability of individuals to acquire and store energy for life-history traits such as reproduction and survival, is finite. This demands prioritizing some traits at the expense of other traits. Which traits to prioritize, depends on the life-history strategy of a species. ‘Slow’-living species, in contrast to ‘fast’-living species, mature late, produce small broods, have low extrinsic mortality and high life expectancy. They tend to allocate resources cautiously to current reproduction, thereby enhancing their survival and potential for future reproduction. Many seabird species employ the slow-living life-history strategy. In order to assess the effects of predicted future climate change on seabird populations, it is important to understand how life-history traits, such as reproduction and survival, are influenced by climatic and environmental variability. The aim of this thesis was to assess the effects of climatic and environmental variability on foraging (i.e. energy acquisition), reproduction and survival of the little auk (Alle alle), the most abundant seabird species breeding in the Arctic. It is in the Arctic regions, where the effects of global climate change are expected to be strongest. Data on oceanographic conditions, foraging trip durations, chick provisioning rates, chick diet, chick fledging success and adult survival was collected on Bjørnøya, a small island in the western Barents Sea, and at three colonies (Isfjorden, Kongsfjorden and Magdalenefjorden) on the western coast of Spitsbergen, Svalbard during 2006-2013. The study area is influenced by both warm, Atlantic and cold, Arctic water masses. The results show that little auk adults preferred to forage in cold water masses at the shelf-sea area, but that oceanographic conditions did not influence their foraging trip durations or chick provisioning rates. On the other hand, the number of good quality prey items delivered daily to a chick correlated negatively with ocean temperature, and both chick fledging success and adult survival was higher when ocean temperature was lower. The higher fledging and survival probabilities were most likely due to higher availability of good quality prey in the little auk’s foraging grounds. Indeed, both these life-history traits seemed highly responsive to changes in environment. High sensitivity indicates that in the future, when Arctic warming is expected to continue and favoured Arctic zooplankton is gradually replaced with Atlantic zooplankton, little auk populations are likely to decrease substantially. This in turn may influence the dynamics of the entire Arctic food web, in which little auks play an important role

Relationships between isotopic ratios, body condition and breeding success in a High Arctic seabird community

Predators such as seabirds are often used as bio-indicators of the marine environment. This is based on the assumption that changes in seabird populations are driven by changes in their prey. We tested this assumption in a High Arctic seabird community by assessing the relationships between the diet, body condition, and breeding performance of 4 ecologically different species: the little auk Alle alle, black-legged kittiwake Rissa tridactyla, Brünnich’s guillemot Uria lomvia, and glaucous gull Larus hyperboreus, breeding in Svalbard, Norway. Interannual changes in seabird diet (2009−2015) were assessed by estimating their carbon and nitrogen isotopic ratios (δ15N and δ13C) during the breeding and non-breeding seasons (i.e. using blood and feather tissues). We found interannual variation in the isotopic ratios during both seasons in all 4 species. These variations differed among species, thus suggesting dietary changes, instead of changes in isotopic baselines, as the most plausible mechanism underlying such patterns. We also found that seabirds had a lower average hatching success when the average δ15N during the previous nonbreeding season was higher. Our results suggest that changes in the average prey composition during the non-breeding season may partially explain changes in breeding performance of Svalbard seabirds.acceptedVersio

Arctic complexity: A case study on diel vertical migration of zooplankton

- © The Author 2014. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited