Two poly(vinylidene fluoride) (PVDF) membrane modification approaches, i.e., poly(vinylpyrrolidone) (PVP) modification and sulfonation, were applied and investigated to produce a fouling-resistant membrane for microalgae filtration. Both methods were able to alter the membrane surface to become more hydrophilic. However, clean water permeance increased only for the PVP-modified membranes, while the sulfonated membranes underwent a significant morphology transformation to a denser membrane and thus lower permeance. Microalgae filtration with PVP-modified membranes showed less fouling compared to the pristine one, particularly in the beginning of the filtration, indicating that fouling reduction on these membranes mainly occurs in the initial fouling stage. Fouling is also found to be influenced by the microalgae species, possibly due to the different properties of the formed cake layer.
Arctic cod (Boreogadus saida) is the most abundant forage fish in the Arctic Ocean. Here we review Arctic cod habitats, distribution, ecology, and physiology to assess how climate change and other anthropogenic stressors are affecting this key species. This review identifies vulnerabilities for different life stages across the entire distribution range of Arctic cod. We explore the impact of environmental (abiotic and biotic) and anthropogenic stressors on Arctic cod with a regional perspective in a scenario up to the year 2050 and identify knowledge gaps constraining predictions. Epipelagic eggs and larvae are more vulnerable to climate change and stressors than adults. Increased water temperatures, sea-ice decline, altered freshwater input, acidification, changing prey field, increased interspecific competition, new predators, and pollution are the principal stressors that will affect Arctic cod populations. Detrimental effects are likely to be greater in regions characterized by the advection of warmer Atlantic and Pacific waters. In contrast, Arctic cod may benefit from ocean warming in colder areas of the High Arctic. The risk from fisheries is moderate and primarily limited to bycatch. Overall, a decrease in suitable habitat and an associated decline in total Arctic cod biomass are predicted. In most Arctic seas, the relative abundance of Arctic cod within the fish community will likely fluctuate in accordance with cold and warm periods. A reduced abundance of Arctic cod will negatively affect the abundance, distribution, and physiological condition of certain predators, whereas some predators will successfully adapt to a more boreal diet. Regional management measures that recognize the critical role of Arctic cod are required to ensure that increased anthropogenic activities do not exacerbate the impacts of climate change on Arctic marine ecosystems. Ultimately, the mitigation of habitat loss for Arctic cod will only be achieved through a global reduction in carbon emissions.
The Arctic marine ecosystem is changing fast due to climate change, emphasizing the need for solid ecological baselines and monitoring. The polar cod Boreogadus saida functions as a key species in the Arctic marine food web. We investigated the stomach contents of polar cod from the northern Barents Sea using DNA metabarcoding with the mitochondrial cytochrome c oxidase I gene in parallel with classical visual analysis. Arctic amphipods and krill dominated the diet in both methods. Yet, metabarcoding allowed for the identification of digested and unidentifiable prey and provided higher taxonomic resolution, revealing new and undiscovered prey items of polar cod in the area. Furthermore, molecular results suggest a higher importance of barnacles and fish (presumably eggs and pelagic larvae) in the diet than previously recorded. Parasites and, in 6 cases, other prey items were only visually identified, demonstrating the complementary nature of both approaches. The presence of temperate and boreal prey species such as northern krill and (early life stages of) European flounder and European plaice illustrates the advection of boreal taxa into the polar region or may be indicative of ongoing borealisation in the Barents Sea. We show that a combination of visual analysis and metabarcoding provides complementary and semi-quantitative dietary information and integrative insights to monitor changing marine food webs.
Climate change is rapidly modifying marine fish assemblages in the Arctic. Since fish eggs and larvae have narrower thermal tolerance than nonreproductive adults, their response to increasing temperatures is likely one of the main drivers of these changes. In this study, we described ichthyoplankton assemblages in West Greenland between 62 and 73 °N, during summers 2017-2019, and investigated the relationship between sea surface temperature in the spring and summer and the survival of Arctic cod (Boreogadus saida) early life stages over the hatching season. Warm years were associated with partial recruitment failures resulting from thermal stress to the eggs and larvae hatched late in the season. Using past environmental conditions, we forecasted an imminent decline in Arctic cod recruitment in the regions of Uummannaq and Disko Bay. Observations from fjords suggested that glacial meltwater could create a subsurface thermal refuge allowing Arctic cod larvae to survive despite very high summer sea surface temperature (ca. 10°C). As the Greenland ice sheet is melting at an unprecedented speed, the mechanism underlying the ″glacial meltwater summer refuge hypothesis″ could curb some of the negative effects of ocean warming on the survival of young Arctic cod in West Greenland and other Arctic fjord systems.
The current and projected environmental change of the Arctic Ocean contrasts sharply with the limited knowledge of its genetic biodiversity. Polar cod Boreogadus saida (Lepechin, 1774) is an abundant circumpolar marine fish and ecological key species. The central role of polar cod in the Arctic marine food web warrants a better understanding of its population structure and connectivity. In this study, the genetic population structure of 171 juveniles, collected from several fjords off West-Svalbard (Billefjorden, Hornsund and Kongsfjorden), the northern Sophia Basin and the Eurasian Basin of the Arctic Ocean, was analysed using nine DNA microsatellite loci.Genetic analyses indicated moderate to high genetic diversity, but absence of spatial population structure and isolation-by-distance, suggesting ongoing gene flow between the studied sampling regions. High levels of connectivity may be key for polar cod to maintain populations across wide spatial scales. The adaptive capacity of the species will be increasingly important to face challenges such as habitat fragmentation, ocean warming and changes in prey composition. In view of a limited understanding of the population dynamics and evolution of polar cod, a valuable next step to predict future developments should be an integrated biological evaluation, including population genomics, a life-history approach, and habitat and biophysical dispersal modelling.
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