Limited effects of changing prey fish communities on food quality for aquatic predators in the eastern Canadian Arctic in terms of essential fatty acids, methylmercury and selenium

Contrasting trophic transfer patterns of cadmium and mercury in the Arctic marine food web of east Hudson Bay, Canada

We investigated trophic transfer of cadmium (Cd) through an Arctic marine food web in Hudson Bay and compared it with mercury (Hg), a metal known to strongly biomagnify. We evaluated blue mussel, sea urchin, common eider, sculpin, Arctic cod, and ringed seal for the influence of dietary and biological variables on variation in Cd and Hg concentrations. Age and size influenced metal concentrations among individuals within a vertebrate species. Consumer carbon and sulfur isotope values were correlated with their Cd and Hg concentrations, indicating habitat-specific feeding influenced metal bioaccumulation. Trophic transfer patterns for Cd depended on the vertebrate tissue, with food web biodilution observed for the muscle but not the liver. Liver Cd concentrations were higher in ringed seal and some common eider relative to prey. In contrast, we observed mercury biomagnification for both tissues. Tissue- and species-specific physiology can explain discrepancies of Cd trophic transfer in this Arctic marine food web.

Changing environmental conditions have altered the feeding ecology of two keystone Arctic marine predators

Environmental change in the Arctic has impacted the composition and structure of marine food webs. Tracking feeding ecology changes of culturally-valued Arctic char (Salvelinus alpinus) and ringed seals (Pusa hispida) can provide an indication of the ecological significance of climate change in a vulnerable region. We characterized how changes in sea ice conditions, sea surface temperature (SST), and primary productivity affected the feeding ecology of these two keystone species over a 13- and 18-year period, respectively, in northern Labrador, Canada. Arctic char fed consistently on pelagic resources (δ13C) but shifted over time to feeding at a higher trophic level (δ15N) and on more marine/offshore resources (δ34S), which correlated with decreases in chlorophyll a concentration. A reduction in Arctic char condition factor and lipid content was associated with higher trophic position. Ringed seals also shifted to feeding at a higher trophic level, but on more pelagic resources, which was associated with lower SST and higher chlorophyll a concentrations. Years with abnormally high SSTs and reduced sea ice concentrations resulted in large isotopic niche sizes for both species, suggesting abrupt change can result in more variable feeding. Changes in abundance and distribution of species long valued by the Inuit of Labrador could diminish food security.

Mercury accumulation, biomagnification, and relationships to δ13C, δ15N and δ34S of fishes and marine mammals in a coastal Arctic marine food web

Combining mercury and stable isotope data sets of consumers facilitates the quantification of whether contaminant variation in predators is due to diet, habitat use and/or environmental factors. We investigated inter-species variation in total Hg (THg) concentrations, trophic magnification slope between δ15N and THg, and relationships of THg with δ13C and δ34S in 15 fish and four marine mammal species (249 individuals in total) in coastal Arctic waters. Median THg concentration in muscle varied between species ranging from 0.08 ± 0.04 μg g-1 dw in capelin to 3.10 ± 0.80 μg g-1 dw in beluga whales. Both δ15N (r2 = 0.26) and δ34S (r2 = 0.19) best explained variation in log-THg across consumers. Higher THg concentrations occurred in higher trophic level species that consumed more pelagic-associated prey than consumers that rely on the benthic microbial-based food web. Our study illustrates the importance of using a multi-isotopic approach that includes δ34S when investigating trophic Hg dynamics in coastal marine systems.

Arctic methylmercury cycling

Anthropogenic mercury (Hg) undergoes long-range transport to the Arctic where some of it is transformed into methylmercury (MeHg), potentially leading to high exposure in some Arctic inhabitants and wildlife. The environmental exposure of Hg is determined not just by the amount of Hg entering the Arctic, but also by biogeochemical and ecological processes occurring in the Arctic. These processes affect MeHg uptake in biota by regulating the bioavailability, methylation and demethylation, bioaccumulation and biomagnification of MeHg in Arctic ecosystems. Here, we present a new budget for pools and fluxes of MeHg in the Arctic and review the scientific advances made in the last decade on processes leading to environmental exposure to Hg. Methylation and demethylation are key processes controlling the pool of MeHg available for bioaccumulation. Methylation of Hg occurs in diverse Arctic environments including permafrost, sediments and the ocean water column, and is primarily a process carried out by microorganisms. While microorganisms carrying the hgcAB gene pair (responsible for Hg methylation) have been identified in Arctic soils and thawing permafrost, the formation pathway of MeHg in oxic marine waters remains less clear. Hotspots for methylation of Hg in terrestrial environments include thermokarst wetlands, ponds and lakes. The shallow sub-surface enrichment of MeHg in the Arctic Ocean, in comparison to other marine systems, is a possible explanation for high MeHg concentrations in some Arctic biota. Bioconcentration of aqueous MeHg in bacteria and algae is a critical step in the transfer of Hg to top predators, which may be dampened or enhanced by the presence of organic matter. Variable trophic position has an important influence on MeHg concentrations among populations of top predator species such as ringed seal and polar bears distributed across the circumpolar Arctic. These scientific advances highlight key processes that affect the fate of anthropogenic Hg deposited to Arctic environments.

Feeding and contaminant patterns of sub-arctic and arctic ringed seals: Potential insight into climate change-contaminant interactions

To provide insight into how climate-driven diet shifts may impact contaminant exposures of Arctic species, we compared feeding ecology and contaminant concentrations in ringed seals (Pusa hispida) from two Canadian sub-Arctic (Nain at 56.5°N, Arviat at 61.1°N) and two Arctic sites (Sachs Harbour at 72.0 °N, Resolute Bay at 74.7 °N). In the sub-Arctic, empirical evidence of changing prey fish communities has been documented, while less community change has been reported in the Arctic to date, suggesting current sub-Arctic conditions may be a harbinger of future Arctic conditions. Here, Indigenous partners collected tissues from subsistence-harvested ringed seals in 2018. Blubber fatty acids (FAs) and muscle stable isotopes (δ¹⁵N, δ¹³C) indicated dietary patterns, while measured contaminants included heavy metals (e.g., total mercury (THg)), legacy persistent organic pollutants (e.g., dichlorodiphenyltrichloroethanes (DDTs)), polybrominated diphenyl ethers (PBDEs), and per-/polyfluoroalkyl substances (PFASs). FA signatures are distinct between sub-Arctic and Resolute Bay seals, likely related to higher consumption of southern prey species including capelin (Mallotus villosus) in the sub-Arctic but on-going feeding on Arctic species in Resolute Bay. Sachs Harbour ringed seals show FA overlap with all locations, possibly consuming both southern and endemic Arctic species. Negative δ¹³C estimates for PFAS models suggest that more pelagic, sub-Arctic type prey (e.g., capelin) increases PFAS concentrations, whereas the reverse occurs for, e.g., THg, ΣPBDE, and ΣDDT. Inconsistent directionality of δ¹⁵N estimates in the models likely reflects baseline isotopic variation not trophic position differences. Adjusting for the influence of diet suggests that if Arctic ringed seal diets become more like sub-Arctic seals due to climate change, diet-driven increases may occur for newer contaminants like PFASs, but not for more legacy contaminants. Nonetheless, temporal trends studies are still needed, as are investigations into the potential confounding influence of baseline isotope variation in spatial studies of contaminants in Arctic biota.

Toxicological risk of mercury for fish and invertebrate prey in the Arctic

We assessed the risks of mercury (Hg) to Arctic marine and freshwater fish by compiling published muscle Hg concentrations and information on tissue concentrations associated with adverse effects. The assessment included 333 groups of fish representing 35 genera and 14,002 individuals sampled from sites across the circumpolar Arctic. Mean or median Hg concentrations in fish muscle varied widely from 0.005 μg/g ww to a maximum of 2.2 μg/g ww. Results indicate that most (n = 139 of 333 or ~ 42%) Arctic fish are not at risk for Hg toxicity, based on the large number of fish mean or median muscle Hg concentrations below 0.1 μg/g ww. A smaller number of the identified groups (n = 76 of 333 or ~ 23%) of Arctic fish had mean or median Hg concentrations consistent with moderate (0.3-0.5 μg/g ww), high (0.5-2 μg/g ww), and severe risk (≥2 μg/g ww). Most of the fish with Hg concentrations in these risk categories were long-lived predators (e.g., non-anadromous Arctic char, northern pike, lake trout, Greenland halibut, Greenland shark). We also, for the first time, conducted a risk assessment of Arctic marine and freshwater invertebrates to evaluate the potential for Hg effects at lower trophic levels and to support risk assessment for Arctic fish. The vast majority (90%) of site-specific Hg or methylmercury (MeHg) concentrations in taxa of marine and freshwater invertebrates (n = 321) were < 0.5 μg/g dw, which is well below critical body residues of Hg in aquatic invertebrates associated with acute and sublethal effects determined in laboratory dosing studies. As the screening-level approach we carried out in the present study is not indicative of actual effects, more studies which directly evaluate the effects of Hg exposure in Arctic fish species are needed. The information here will be of use to Article 22 (Effectiveness Evaluation) of the Minamata Convention.

Climate change and mercury in the Arctic: Biotic interactions

Global climate change has led to profound alterations of the Arctic environment and ecosystems, with potential secondary effects on mercury (Hg) within Arctic biota. This review presents the current scientific evidence for impacts of direct physical climate change and indirect ecosystem change on Hg exposure and accumulation in Arctic terrestrial, freshwater, and marine organisms. As the marine environment is elevated in Hg compared to the terrestrial environment, terrestrial herbivores that now exploit coastal/marine foods when terrestrial plants are iced over may be exposed to higher Hg concentrations. Conversely, certain populations of predators, including Arctic foxes and polar bears, have shown lower Hg concentrations related to reduced sea ice-based foraging and increased land-based foraging. How climate change influences Hg in Arctic freshwater fishes is not clear, but for lacustrine populations it may depend on lake-specific conditions, including interrelated alterations in lake ice duration, turbidity, food web length and energy sources (benthic to pelagic), and growth dilution. In several marine mammal and seabird species, tissue Hg concentrations have shown correlations with climate and weather variables, including climate oscillation indices and sea ice trends; these findings suggest that wind, precipitation, and cryosphere changes that alter Hg transport and deposition are impacting Hg concentrations in Arctic marine organisms. Ecological changes, including northward range shifts of sub-Arctic species and altered body condition, have also been shown to affect Hg levels in some populations of Arctic marine species. Given the limited number of populations and species studied to date, especially within Arctic terrestrial and freshwater systems, further research is needed on climate-driven processes influencing Hg concentrations in Arctic ecosystems and their net effects. Long-term pan-Arctic monitoring programs should consider ancillary datasets on climate, weather, organism ecology and physiology to improve interpretation of spatial variation and time trends of Hg in Arctic biota.

Resource recovery from fish waste: Prospects and the usage of intensified extraction technologies

Globally, the valorization of fish biowaste as a feedstock to recover valuable components is an emerging research and commercial interest area to achieve the SDG goals by 2030. Fish waste-derived biomolecules are increasingly finding diverse applications in food and other biotechnological fields due to their excellent chemical, structural and functional properties. The focus of this review is to highlight the conventional valorization routes and recent advancements in extraction technologies for resource recovery applications, primarily focusing on green processes. Biointensified processes involving ultrasound, microwave, sub- and supercritical fluids, pulsed electric field, high-pressure processing, and cold plasma are extensively explored as sustainable technologies for valorizing fish discards and found numerous applications in the production of functional and commercially important biomaterials. With challenges in recovering intracellular bioactive compounds, selectivity, and energy requirement concerns, conventional approaches are being relooked continuously in the quest for process intensification and sustainable production practices. Nonetheless, in the context of 'zero waste' and 'biorefinery for high-value compounds', there is immense scope for technological upgradation in these emerging alternative approaches. This work details such attempts, providing insights into the immense untapped potential in this sector.

Measurable Levels of Short-Chain Chlorinated Paraffins in Western Hudson Bay Fishes but Limited Biomagnification from Fish to Ringed Seals

We investigated short-chain (C_10-13 ) chlorinated paraffins (SCCP) in an Arctic marine food web. In zooplankton, fishes, and ringed seals from western Hudson Bay, Canada, SCCP concentrations ranged from 38.3 to 687 ng g^-1 lipid weight. Monte Carlo-simulated trophic-adjusted biomagnification factors of individual SCCP congeners ranged from 0.07 to 0.55 for small pelagic fishes to seals. Despite relatively high concentrations in fishes, biomagnification of SCCPs within this food web appears limited. Environ Toxicol Chem 2021;40:2990-2999. © 2021 SETAC.

Susceptibility to Oxidation of Selected Freshwater Fish Species Lipids as a Potential Source of Fish Oil in Dietary Supplements

Polyunsaturated fatty acids from the omega 3 family are more and more often supplied to the diet in the form of supplements. The aim of the study was to characterize the lipid fractions of predatory freshwater fish, i.e., pike (Esox lucius L.), perch (Perca fluviatilis L.), and pike perch (Sander lucioperca L.), and omnivorous fish, i.e., bream (Abramis brama L.) and roach (Rutilus rutilus L.). Their technological usefulness in terms of the source of fish oil was determined, depending on the rate and degree of their oxidative changes. UV radiation (photooxidation test) was used as a factor accelerating lipid oxidation. Research has shown that selected species of freshwater fish are characterized by high lipid oxidative stability, due to the availability and speed of delivery to the processing plant. The initial level of lipid oxidation of their meat, expressed by the TOTOX index, in any species did not exceed the value of 7, while the acceptable value was 26. The oil obtained from the meat of omnivorous fish after the photooxidation process was characterized by significantly better oxidative stability compared to the oil from the meat of predatory fish. The oxidation resistance of omnivorous fish oil was shown to be higher than that of predatory fish.

Monthly variations in mercury exposure of school children and adults in an industrial area of southwestern China

Recent studies have shown that rice consumption can be the major pathway for human methylmercury (MeHg) exposure in inland China. However, few studies have considered the susceptible population of school children's exposure through rice ingestion. In this study, monthly variations in total Hg (THg)/MeHg concentrations in rice, fish, hair, and urine samples were studied to evaluate the Hg (both THg and MeHg) exposure in Guiyang, a typical industrial area with high anthropogenic emission of Hg. A total of 17 primary school (school A) students, 29 middle school (school B) students, and 46 guardians participated in this study for one year. Hair THg, hair MeHg, and urine THg concentrations ranged from 355-413 ng g^-1, 213-236 ng g^-1, and 469-518 ng g^-1 Creatinine (ng·g^-1 Cr), respectively, and no significant differences were observed between different genders and age groups. Hair and urine Hg concentrations showed slightly higher values in the cold season (October to February) than the hot season (March to September), but without significant difference. High monthly variability of individual hair and urine Hg concentrations suggested that long-term study could effectively decrease the uncertainty. The school students showed significantly higher urine THg concentrations than adults due to children's unique physiological structure and behaviors. Probable daily intake (PDI) of MeHg via rice and fish ingestion averaged at 0.0091, 0.0090, and 0.0079 μg kg^-1 d^-1 for school A students, school B students, and their guardians, respectively, which means that 86%, 84%, and 87% of the PDI were originated from rice ingestion, respectively. Therefore, more attention should be paid to children as a susceptible population. The results indicated low risk of Hg exposure via rice and fish consumption for urban residents in a Chinese industrial city.

Habitat and resource segregation of two sympatric seals in the North Sea

The study of ecological niche segregation in sympatric species is essential to understand ecosystem functioning and its response to potential changes. In the North Sea, sympatric grey and harbour seals may present competition for food resources sustained by intense fishing activities and recent increase of seal populations. In order to coexist and reduce inter-specific competition, sympatric species must segregate at least one aspect of their ecological niches: temporal, spatial or resource segregation. We aim to study the foraging resources and foraging distributions of grey seals and harbour seals and the potential competition between these species in the North Sea. Therefore, we analysed stable isotopic composition of C, N and S (δ¹³C, δ¹⁵N and δ³⁴S values), and the concentrations of Hg and Se in blood of harbour and grey seals from the North Sea. Blood samples were collected on 45 grey seals and 37 harbour seals sampled along German and Scottish coasts. Stable isotope ratios were performed with an isotope ratio mass spectrometer coupled to an N-C-S elemental analyser for automated analyses. Total mercury concentrations (T-Hg) were determined by atomic absorption spectroscopy and Se concentrations by ICP-MS. The multi-tracer approach shown spatial and resource partitioning within grey and harbour seal living along German and Scottish coasts. Data indicate 1) the offshore foraging distribution of grey seals as reflected by the lower δ¹⁵N values and T-Hg concentrations and higher Se concentrations and 2) the inshore foraging distribution of harbour seals because of higher δ¹⁵N values and T-Hg concentrations and lower Se concentrations. The SIAR mixing model revealed 3) a more selective diet of grey seals compared to harbour seals and 4) the importance of sandeels in grey seal diet reflected by their high δ³⁴S values. Lastly, diet ellipse overlaps between grey seals and harbour seals sampled along the German coasts suggested 5) a potential sharing of food resources, possibly due to the increase number of grey seals number in this area during the foraging season - all year except breeding and moulting periods. The multi-tracer approach of this study provides a more robust discrimination among diet resources and spatial foraging distributions of grey seals and harbour seals in the North Sea.