Jasmine Nahrgang

Is the poleward expansion by Atlantic cod and haddock threatening native polar cod, Boreogadus saida ?

During a recent period of increased influx of warm Atlantic water to the western coast of Svalbard, we have observed a northward expansion of boreal Atlantic cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) into areas dominated by the native polar cod (Boreogadus saida). To determine the potential impact of new ecological interactions, we studied the diet of co-occurring juvenile gadoids in fjords, open water, and sea ice around Svalbard. We also reviewed the available literature on polar cod feeding in different habitats across the Arctic to determine whether region, habitat, or fish size may influence diet. Feeding by polar cod in the pelagic zone was size dependent, with small fish primarily consuming Calanus spp. and smaller copepods, with an increasing ration of Themisto spp. at larger sizes. In benthic habitats, diets were more varied and included considerably more unidentified material and sediment. Less than 40% dietary overlap was detected among the three species when they were found together. Stable isotope analyses indicated these patterns were representative of longer-term assimilation. The low interspecific dietary overlap suggests little direct competition. Future increases in abundance and the high predation potential of the boreal taxa, however, may impact the persistence of polar cod on some Arctic shelves.

PAH biomarker responses in polar cod (Boreogadus saida) exposed to benzo(a)pyrene

With expanding oil and gas activities into the Arctic region, there is a need to evaluate the induction capacity of polycyclic aromatic hydrocarbon (PAH) biomarkers on Arctic marine organisms and to test analytical methods that have been optimized for their temperate counterparts. Polar cod Boreogadus saida were injected intraperitoneally with cod liver oil (solvent control), 6.6+/-3.7, 85+/-48 or 378+/-190 microg kg(-1) wet weight of benzo(a)pyrene (B(a)P), or not injected (control), and liver and bile were sampled at 0 and 16 h and 1, 2, 4 and 7d. The mRNA expression of cytochrome P4501A1 (cyp1a1) and glutathione S-transferase (gst) genes showed a dose-dependent induction in the first 16 h following the injection and a return to basal levels after 4d. The aryl hydrocarbon receptor 2, however, showed no change in mRNA expression. The protein quantification of cytochrome P4501A (CYP1A), through Western blot analysis and the enzyme-linked immunosorbent assay (ELISA), presented similar but weaker and time-delayed responses (4-7d) compared to the gene (16 h to 2d). Ethoxyresorufin O-deethylase (EROD) and glutathione S-transferase (GST) activities increased significantly at day 7 following the gene induction and increase in protein levels. Overall, these biomarkers showed dose-dependent but weak responses to B(a)P and low levels of bile metabolites. The mRNA expressions of oxidative stress genes, superoxide dismutases (sod(Cu/Zn) and sod(Mn)), catalase (cat) and glutathione peroxidase (gpx), were all up-regulated between 16 h and 2d of B(a)P exposure with cat (72-fold) and sod(Cu/Zn) (20-fold) giving the strongest responses in the highest dose. Finally, CAT protein level and enzyme activities showed less clear responses than the genes. The mRNA expression showed the earliest responses, followed by the protein levels. The enzymatic activities were the least sensitive and responded to the exposure after 7d. The study shows the induction capability of biomarkers in polar cod at very low bioavailable doses of B(a)P and provides new information on the selected biomarkers for use in oil monitoring in the Arctic.

Seasonal variation in biomarkers in blue mussel (Mytilus edulis), Icelandic scallop (Chlamys islandica) and Atlantic cod (Gadus morhua)—Implications for environmental monitoring in the Barents Sea

In the Barents Sea, the limited data on biological relevant indicators and their responses to various anthropogenic stressors have hindered the development of a consistent scientific basis for selecting indicator species and developing practical procedures for environmental monitoring. Accordingly, the main aim of the present study was to develop a common set of baseline values for contaminants and biomarkers in three species, and to identify their strengths and limitations in monitoring of the Barents Sea. Blue mussel (Mytilus edulis), Icelandic scallop (Chlamys islandica) and Atlantic cod (Gadus morhua) were sampled from a north Norwegian fjord in March, June, September and December 2010. Digestive glands from the bivalve species and liver from Atlantic cod were analysed for biomarkers of oxidative stress (catalase [CAT], glutathione peroxidase [GPX], glutathione-S-transferase activities [GST], lipid peroxidation as thiobarbituric reactive substances [TBARS] and total oxyradical scavenging capacity [TOSC]), biotransformation (ethoxyresorufine-O-deethylase activity [EROD]) and general stress (lysosomal membrane stability [LMS]). Concentrations of polycyclic aromatic hydrocarbons (PAHs) and metals in the bivalves and PAH metabolites in fish bile were quantified. Finally, energy reserves (total lipids, proteins and carbohydrates) and electron transport system (ETS) activity in the digestive gland of the bivalves and liver of Atlantic cod provided background information for reproductive cycle and general physiological status of the organisms. Blue mussel and Icelandic scallop showed very similar trends in biological cycle, biomarker expression and seasonality. Biomarker baselines in Atlantic cod showed weaker seasonal variability. However, important biological events may have been undetected due to the large time intervals between sampling occasions. Physiological biomarkers such as energy reserves and ETS activity were recommended as complementary parameters to the commonly used stress biomarkers, as they provided valuable information on the physiological status of the studied organisms. Interpretation of the seasonality in oxidative stress biomarkers was in general difficult but TOSC and lipid peroxidation were preferred over the antioxidant enzyme activities. This study is the first reporting seasonal baseline in these three species in a sub-Arctic location. Overall, the Icelandic scallop was considered the most adequate organism for environmental monitoring in the Barents Sea due to the interpretability of the biomarker data as well as its abundance, ease to handle and wide distribution from the southern Barents Sea to Svalbard.

Biomarker responses in polar cod (Boreogadus saida) exposed to the water soluble fraction of crude oil.

In order to mimic the biological effects of an oil spill in Arctic waters, we examined several types of biomarkers (genes, enzymes, metabolites, and DNA damage) in polar cod Boreogadus saida experimentally exposed to the water soluble fractions of crude oil. During 4 weeks of exposure, induction of the studied biomarkers exceeded baseline levels. The mRNA expression of the cytochrome P4501A1 (cyp1a1) gene was the most promising biomarker, with glutathione S-transferase (gst) as a suitable complement. The delayed ethoxyresorufin O-deethylase (EROD) and GST activities and their persistence following 2 weeks of depuration may allow detection of previous exposures in field samples. The composition of PAH metabolites in the bile indicated the bioavailability of different PAH size-classes. Although mRNA expressions of antioxidant defense genes were induced at start of the exposure, with the strongest responses from catalase and cytosolic superoxide dismutase, they were poor for oil monitoring purposes due to their very short response times. Significant DNA damage demonstrated genotoxicity even at low PAH concentrations (<15microgL(-1)) and was correlated with benzo(a)pyrene and pyrene metabolites in the bile.

Biomarker responses in polar cod (Boreogadus saida) exposed to dietary crude oil.

Polar cod Boreogadus saida were exposed weekly to two doses of dietary crude oil for 4 weeks followed by 2 weeks of depuration. Administered doses corresponded on average to 4 and 9microgSigmaPAHsg(-1)fishweek(-1). Cytochrome P4501A1 (cyp1a1) and glutathione S-transferase (gst) mRNA expression, ethoxyresorufin O-deethylase (EROD) activity and metabolites in the bile showed strong and dose-dependent inductions at 2 and 4 weeks of exposure. Following 2 weeks depuration, mRNA expression of cyp1a1 and gst and PAH metabolites returned to basal levels while EROD activity and GST activity were still induced in the high oil treatment. The mRNA expressions of antioxidant defense genes (catalase, glutathione peroxidase and cytosolic and mitochondrial superoxide dismutase) did not change significantly during the experiment. Catalase activity was significantly depressed at week 2 in the high oil treatment. We conclude that the cyp1a1 mRNA expression, EROD activities and bile metabolites were the most reliable biomarkers of exposure while gst mRNA expression and GST activity were less sensitive and are considered only as complementary. Antioxidant defenses were poor biomarkers to assess effects of crude oil exposure in polar cod.

Seasonal baseline levels of physiological and biochemical parameters in polar cod (Boreogadus saida): Implications for environmental monitoring.

Seasonality of biomarker baseline levels were studied in polar cod (Boreogadus saida), caught in Kongsfjorden, Svalbard, in April, July, September and December, 2006-2007. Physiological parameters (condition factor, gonado- and hepato-somatic indexes, energy reserves, potential metabolic activity and antifreeze activity) in polar cod were used to interpret the seasonality of potential biomarkers. The highest levels of ethoxyresorufin-O-deethylase (EROD) activity occurred concomitantly with the highest potential metabolic activity in July due to e.g. intense feeding. During pre-spawning, EROD showed significant inhibition and gender differences. Hence, its potential use in environmental monitoring should imply gender differentiation at least during this period. Glutathione S-transferase and catalase activities were stable from April to September, but changed in December suggesting a link to low biological activity. Knowledge of the biomarker baseline levels and their seasonal trends in polar cod is essential for a trustworthy interpretation of forthcoming toxicity data and environmental monitoring in the Arctic.

Gender specific reproductive strategies of an arctic key species (Boreogadus saida) and implications of climate change

The Arctic climate is changing at an unprecedented rate. What consequences this may have on the Arctic marine ecosystem depends to a large degree on how its species will respond both directly to elevated temperatures and more indirectly through ecological interactions. But despite an alarming recent warming of the Arctic with accompanying sea ice loss, reports evaluating ecological impacts of climate change in the Arctic remain sparse. Here, based upon a large-scale field study, we present basic new knowledge regarding the life history traits for one of the most important species in the entire Arctic, the polar cod (Boreogadus saida). Furthermore, by comparing regions of contrasting climatic influence (domains), we present evidence as to how its growth and reproductive success is impaired in the warmer of the two domains. As the future Arctic is predicted to resemble todays Atlantic domains, we forecast changes in growth and life history characteristics of polar cod that will lead to alteration of its role as an Arctic keystone species. This will in turn affect community dynamics and energy transfer in the entire Arctic food chain.

Toxicity of crude oil and pyrene to the embryos of beach spawning capelin (Mallotus villosus)

Due to a northward shift in oil and gas activities, there is an increasing need to understand the potential anthropogenic impacts of oil-related compounds on sub-Arctic and Arctic organisms, particularly those in coastal habitats. Capelin (Mallotus villosus), a key fish species in the Barents Sea ecosystem, undertakes aggregated spawning at both intertidal and subtidal coastal localities in northern Norway. To investigate the sensitivity of capelin embryos to oil compounds, newly fertilized capelin eggs were collected from a spawning beach and exposed until hatch (32 days) to either the water soluble fraction of crude oil or the single PAH compound, pyrene. Threshold levels for egg mortality, development and hatching success were determined. Concentrations of 40 μg/L crude oil (∑26 PAHs) and 55 μg/L pyrene significantly increased embryonic mortality rates and decreased hatching success, compared with controls, indicating that a potential oil spill in the vicinity of capelin spawning grounds may cause significant impacts. No significant incidence of adverse effects such as yolk sac oedema, pericardia oedema, haemorrhages, craniofacial abnormalities, premature hatch or inhibited growth was observed. Histological studies of hatched larvae did not reveal specific sublethal effects in tissues and organs. Developmental delays and subsequent embryo death were noticed at the period of eye pigmentation in affected groups. Early life-history stages of capelin are sensitive indicators of PAH impacts, but the mechanisms responsible for the toxic effects require further investigation.

EROD activity in liver and gills of polar cod (Boreogadus saida) exposed to waterborne and dietary crude oil.

Polar cod Boreogadus saida an indicator species for biomonitoring in the Arctic was exposed to crude oil in waterborne and dietary experiments. Ethoxyresorufin O-deethylase (EROD) activity was measured in liver and gills of polar cod at weeks 0, 2 and 4 of exposure and following 2 weeks of depuration. EROD increased significantly and dose-dependently in both tissues through both exposure routes. Levels were very low in gills compared to liver reflecting the tissue-specific metabolism capacities and tissue-specific response kinetics were also observed. Furthermore, a significant increase of gill EROD was shown in dietary exposed fish, demonstrating a substantial transport of PAHs via the systemic circulation. To conclude, this study gave some preliminary information on the EROD response in terms of levels, dose dependency and timing, in gills of PAH exposed polar cod.

In Vivo Effects of Environmental Concentrations of Produced Water on the Reproductive Function of Polar Cod (Boreogadus saida)

Offshore oil and gas drilling processes generate operational discharges such as produced water (PW), a complex mixture of seawater with polycyclic aromatic hydrocarbons (PAH) and alkylphenols (AP). Some of these compounds may interact with the endocrine system of marine organisms and alter reproductive functions. In this study, polar cod were exposed for up to 28 d to a mixture of PAH, alkylated PAH, and AP simulating the composition of North Sea PW, at low and high concentrations (1:2000 and 1:1000 dilution of the original concentrate, respectively). Potential adverse effects of PW on polar cod physiology were investigated through biomarkers of biotransformation (hepatic ethoxyresorufin O-deethylase [EROD] activity and bile PAH metabolites), endocrine disruption (plasma vitellogenin [VTG] levels and sex steroid concentrations), and gonad histology. Plasma sexual steroid levels in fish were not markedly affected by PW exposure, while higher plasma VTG concentrations were measured in females exposed to the high PW treatment for 7 and 28 d. In males exposed to the higher PW concentration, inhibition of spermatogenesis was observed after 28 d in addition to increase of melano-macrophage occurrence in testis. Females exposed to the high PW treatment for 21 d showed a significant increase of atresia incidence. Finally, a significant decrease in oocyte number was observed in high PW exposed female ovaries after 28 d of exposure.