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Cold‐water lakes situated in high latitudes and altitudes have pivotal socio‐ecological importance both globally and locally. However, they are increasingly threatened by multiple anthropogenic stressors, such as climate change, hydropower and invasive species. The development of efficient management strategies is therefore urgently needed and requires a comprehensive understanding of the factors influencing the biodiversity and ecological processes of these ecosystems. We provide a holistic knowledge base for informed future research and management by addressing the interplay between local and global environmental drivers of food webs in Arctic charr (Salvelinus alpinus, Salmonidae) and brown trout (Salmo trutta, Salmonidae) dominated cold‐water lakes in Fennoscandia. The trophic niche and population dynamics of these generalist top consumers provide extensive insights into the effects of natural and anthropogenic drivers on food webs in intensively studied Fennoscandian cold‐water lakes, covering marked biogeographical gradients in abiotic and biotic conditions. Drawing on a synthesis of existing literature, our focus is on three pivotal drivers: (1) lake location and connectivity, (2) lake area and morphometry and (3) fish community composition. These drivers significantly influence the complexity and the origin and flow of energy in lake food webs, and ultimately the size structure of the charr and trout populations. Furthermore, we highlight ongoing environmental changes in Fennoscandian cold‐water lakes caused by hydropower and invasive species. Finally, we identify crucial knowledge gaps and propose management actions for improving the future state of Fennoscandian cold‐water lake ecosystems and their charr and trout populations. [ABSTRACT FROM AUTHOR]

Our understanding of the environmental behavior, bioaccumulation and concentrations of chlorinated paraffins (CPs) and Dechloranes (Dec) in the Arctic environment is still limited, particularly in freshwater ecosystems. In this descriptive study, short chain (SCCPs) and medium chain (MCCPs) CPs, Dechlorane Plus (DP) and analogues, and polychlorinated biphenyls (PCBs) were measured in sediments, benthic organisms, three-spined stickleback (Gasterosteus aculeatus), Arctic char (Salvelinus alpinus) and brown trout (Salmo trutta) in two Sub-Arctic lakes in Northern Norway. Takvannet (TA) is a remote lake, with no known local sources for organic contaminants, while Storvannet (ST) is situated in a populated area. SCCPs and MCCPs were detected in all sediment samples from ST with concentration of 42.26--115.29 ng/g dw and 66.18--136.69 ng/g dw for SCCPs and MCCPs, respectively. Only SCCPs were detected in TA sediments (0.4--5.28 ng/g dw). In biota samples, sticklebacks and benthic organisms showed the highest concentrations of CPs, while concentrations were low or below detection limits in both char and trout. The congener group patterns observed in both lakes showed SCCP profiles dominated by higher chlorinated congener groups while the MCCPs showed consistency in their profiles, with C14 being the most prevalent carbon chain length. Anti- and syn-DP isomers were detected in all sediment, benthic and stickleback samples with higher concentrations in ST than in TA. However, they were only present in a few char and trout samples from ST. Dec 601 and 604 were below detection limits in all samples in both lakes. Dec 603 was detected only in ST sediments, sticklebacks and 2 trout samples, while Dec 602 was the only DP analogue found in all samples from both lakes. While there were clear differences in sediment concentrations of DP and Dec 602 between ST and TA, differences between lakes decreased with increasing δ15N. This pattern was similar to the PCB behavior, suggesting the lake characteristics in ST are playing an important role in the lack of biomagnification of pollutants in this lake. Our results suggest that ST receives pollutants from local sources in addition to atmospheric transport. [ABSTRACT FROM AUTHOR]

Climate warming causes shorter winters and changes in ice and snow cover in subarctic lakes, highlighting the need to better understand under-ice ecosystem functioning. The plankton community in a subarctic, oligotrophic lake was studied throughout the ice-covered season, focusing on lipid dynamics and life history traits in two actively overwintering copepods, Cyclops scutifer and Eudiaptomus graciloides. Whereas C. scutifer was overwintering in C-IV to C-V stage, E. graciloides reproduced under ice cover. Both species had accumulated lipids prior to ice-on and showed a substantial decrease in total lipid content throughout the ice-covered period: E. graciloides (60%–38% dw) and C. scutifer (73%–33% dw). Polyunsaturated fatty acids of algal origin were highest in E. graciloides and declined strongly in both species. Stearidonic acid (18:4n-3) content in E. graciloides was particularly high and decreased rapidly during the study period by 50%, probably due to reproduction. The copepods differed in feeding behavior, with the omnivore C. scutifer continuing to accumulate lipids until January, whereas the herbivorous E. graciloides accumulated lipids from under-ice primary production during the last months of ice-cover. Our findings emphasize the importance of lipid accumulation and utilization for actively overwintering copepods irrespective of the timing of their reproduction. [ABSTRACT FROM AUTHOR]

We analysed data of a globally distributed model organism (brown trout, Salmo trutta) in an attempt to understand relationships among biogeography, prey communities, and climate on diet composition at regional spatial scales (Scandinavia) and thereafter explored whether diet patterns remained the same at global scales. At regional scales, we uncovered comprehensive patterns in diet composition among neighbouring freshwater ecoregions, with site-specific prey communities as the best predictor of the observed prey utilization patterns. Thus, we posit that environmental gradients altering site-specific prey communities and consequently the trophic niche of the predator through bottom-up mechanisms are key in understanding spatial dietary patterns. Proximity was also important for the revealed biogeographic patterns at global scales. We suggest that geographic location (latitude and elevation) as a proxy of environmental heterogeneity is key at small spatial scales, and climate at global extents, to understand spatial dietary patterns. Our findings support the hypothesis that future shifts in prey communities due to climate change will strengthen biographical patterns in feeding of freshwater fishes, with consequences for invasiveness assessment and nature management and conservation. Nous avons analyse des donnees sur un organisme modele a repartition planetaire (la truite brune, Salmo trutta) pour tenter de comprendre les relations de la biogeographie, des communautes de proies et du climat avec la composition du regime alimentaire a des echelles spatiales regionales (la Scandinavie), puis nous avons examine si les motifs de repartition des regimes alimentaires demeurent les memes a des echelles planetaires. Aux echelles regionales, nous avons releve des motifs comparables de composition du regime alimentaire entre ecoregions d'eau douce voisines, les communautes de proies propres au site constituant le meilleur predicteur des motifs d'utilisation des proies observes. Nous postulons donc que des gradients environnementaux qui modifient les communautes de proies propres au site et, consequemment, par l'entremise de mecanismes ascendants, la niche trophique du predateur sont d'importance cle pour la comprehension des motifs de repartition spatiale des regimes alimentaires. La proximite est aussi importante pour les motifs biogeographiques releves a des echelles planetaires. Nous suggerons que l'emplacement geographique (latitude et altitude) comme variable substitutive de l'heterogeneite environnementale a petite echelle et le climat a l'echelle planetaire revetent une importance cle pour la comprehension de la repartition spatiale des regimes alimentaires. Nos constatations appuient l'hypothese selon laquelle les modifications futures des communautes de proies dues aux changements climatiques renforceront les motifs biogeographiques d'alimentation des poissons d'eau douce, ce qui aura des consequences sur revaluation du potentiel d'envahissement et sur la gestion et la conservation des milieux naturels. [Traduit par la Redaction], Introduction Knowledge of the feeding habits of fish populations is essential to understand their ecological role in food webs and their potential carrying capacity, which in turn is critical for [...]

Host density, host body size and ambient temperature have all been positively associated with increases in parasite infection. However, the relative importance of these factors in shaping long‐term parasite population dynamics in wild host populations is unknown due to the absence of long‐term studies. Here, we examine long‐term drivers of gill lice (Copepoda) infections in Arctic charr (Salmonidae) over 32 years. We predicted that host density and body size and water temperature would all positively affect parasite population size and population growth rate. Our results show that fish size was the main driver of gill lice infections in Arctic charr. In addition, Arctic charr became infected at smaller sizes and with more parasites in years of higher brown trout population size. Negative intraguild interactions between brown trout and Arctic charr appear to drive smaller Arctic charr to seek refuge in deeper areas of the lake, thus increasing infection risk. There was no effect of host density on the force of infection, and the relationship between Arctic charr density and parasite mean abundance was negative, possibly due to an encounter‐dilution effect. The population densities of host and parasite fluctuated independently of one another. Water temperature had negligible effects on the temporal dynamics of the gill lice population. Understanding long‐term drivers of parasite population dynamics is key for research and management. In fish farms, artificially high densities of hosts lead to vast increases in the transmission of parasitic copepods. However, in wild fish populations fluctuating at natural densities, the surface area available for copepodid attachment might be more important than the density of available hosts. [ABSTRACT FROM AUTHOR]