From clear lakes to murky waters - tracing the functional response of high-latitude lake communities to concurrent 'greening' and 'browning'.

Climate change and the intensification of land use practices are causing widespread eutrophication of subarctic lakes. The implications of this rapid change for lake ecosystem function remain poorly understood. To assess how freshwater communities respond to such profound changes in their habitat and resource availability, we conducted a space-for-time analysis of food-web structure in 30 lakes situated across a temperature-productivity gradient equivalent to the predicted future climate of subarctic Europe (temperature +3°C, precipitation +30% and nutrient +45 µg L-1 total phosphorus). Along this gradient, we observed an increase in the assimilation of pelagic-derived carbon from 25 to 75% throughout primary, secondary and tertiary consumers. This shift was overwhelmingly driven by the consumption of pelagic detritus by benthic primary consumers and was not accompanied by increased pelagic foraging by higher trophic level consumers. Our data also revealed a convergence of the carbon isotope ratios of pelagic and benthic food web endmembers in the warmest, most productive lakes indicating that the incorporation of terrestrial derived carbon into aquatic food webs increases as land use intensifies. These results, reflecting changes along a gradient characteristic of the predicted future environment throughout the subarctic, indicate that climate and land use driven eutrophication and browning are radically altering the function and fuelling of aquatic food webs in this biome.

On the challenges and opportunities facing fish biology: a discussion of five key knowledge gaps.

Many fish species face increasing challenges associated with climate change and overfishing. At the same time, aquaculture is becoming vital for food security. Gaining a deeper understanding of the basic biology of fish is therefore more important than ever. Here we synthesize and summarize key questions, opportunities and challenges in fish biology highlighted during a round-table discussion at the 50th Anniversary Symposium of The Fisheries Society of the British Isles, held at the University of Exeter, U.K., in July 2017. We identified several knowledge gaps but also key opportunities for fish biology to inform food security, for collective behaviour, evolutionary history and trait correlations to predict responses to environmental change and for novel analytical approaches to mine existing data sets. Overall, more integrative approaches through stronger collaborations across different fields are needed to advance our understanding of the basic biology of fish.

Inter and intra-population phenotypic and genotypic structuring in the European whitefish Coregonus lavaretus, a rare freshwater fish in Scotland.

This study revealed between-lake genetic structuring between Coregonus lavaretus collected from the only two native populations of this species in Scotland, U.K. (Lochs Eck and Lomond) evidenced by the existence of private alleles (12 in Lomond and four in Eck) and significant genetic differentiation (FST = 0·056) across 10 microsatellite markers. Juvenile C. lavaretus originating from eggs collected from the two lakes and reared in a common-garden experiment showed clear phenotypic differences in trophic morphology (i.e. head and body shape) between these populations indicating that these characteristics were, at least partly, inherited. Microsatellite analysis of adults collected from different geographic regions within Loch Lomond revealed detectable and statistically significant but relatively weak genetic structuring (FST = 0·001-0·024) and evidence of private alleles related to the basin structure of the lake. Within-lake genetic divergence patterns suggest three possibilities for this observed pattern: (1) differential selection pressures causing divergence into separate gene pools, (2) a collapse of two formerly divergent gene pools and (3) a stable state maintained by balancing selection forces resulting from spatial variation in selection and lake heterogeneity. Small estimates of effective population sizes for the populations in both lakes suggest that the capacity of both populations to adapt to future environmental change may be limited.

Multiple exposure of the Boreogadus saida from bessel fjord (NE Greenland) to legacy and emerging pollutants.

This work investigates the occurrence of OCPs, such as hexachlorocyclohexane (α-, ß-, γ- and δ-HCH) isomers, dichlorodiphenyltrichloroethane (p,p'-DDT) and its metabolite dichlorodiphenyldichloroethylene (p,p'-DDE), endosulfan (α- and ß-EDS) isomers, chlorpyrifos (CPF), dacthal (DAC) and phenolic compounds, such as 4-nonylphenol (4-NP) and its precursors nonylphenol polyethoxylates (NP1EO and NP2EO) and bisphenol A (BPA), in polar cod sampled in and outside Bessel Fjord (NE Greenland). Linear regressions between target contaminants and morphological parameters (age, length, weight, gonad- and hepato-somatic indices and Fulton K) have been also evaluated. Polar cod collected at shelf had higher average concentrations of BPA, NP1EO, NP2EO and 4-NP (muscle: 6.2, 13.2, 8.9 and 1.9 ng/g w.w., respectively; liver: 5.8, 7.5, 5.2 and 0.9 ng/g w.w. respectively), than fjord's specimens (muscle: 3.5, 9.1, 3.9 and 1.0 ng/g w.w., respectively; liver: 2.4, 5.3, 2.9 and 1.1 ng/g w.w. respectively). ΣHCHs, ΣEDSs, ΣDDTs, CPF and DAC, were more accumulated in the polar cod from the fjord (average amount in muscle: 9.1, 4.8, 7.9, 3.8 and 2.8 ng/g w.w., respectively; average amount in the liver: 11.2, 9.0, 3.8, 5.9 and 4.9 ng/g w.w., respectively) than shelf's ones (average amount in muscle 3.9, 4.5, 4.2, 0.9 and 1.2 ng/g w.w., respectively; average amount in liver 7.8, 6.3, 2.1, 3.4 and 2.5 ng/g w.w., respectively). The comparison between the concentration of target contaminants and morphologic parameters suggested a different exposure of polar cod occupying the fjord and shelf habitats, due to a combination of genetic and dietary differences, climate change effects and increased human activities.

Cold tolerance in sealworm ( Pseudoterranova decipiens) due to heat-shock adaptations.

Third-stage larvae of Pseudoterranova decipiens commonly infect whitefish such as cod, and the parasite can be transferred to humans through lightly prepared (sushi) meals. Because little is known about the nematode's cold tolerance capacity, we examined the nematode's ability to supercool, and whether or not cold acclimation could induce physiological changes that might increase its ability to tolerate freezing conditions. Even if third-stage Pseudoterranova decipiens larvae have some supercooling ability, they show no potential for freezing avoidance because they are not able to withstand inoculative freezing. Still, they have the ability to survive freezing at high subzero temperatures, something which suggests that these nematodes have a moderate freeze tolerance. We also show that acclimation to high temperatures triggers trehalose accumulation to an even greater extent than cold acclimation. Trehalose is a potential cryoprotectant which has been shown to play a vital role in the freeze tolerance of nematodes. We suggest that the trehalose accumulation observed for the cold acclimation is a general response to thermal stress, and that the nematode's moderate freeze tolerance may be acquired through adaptation to heat rather than coldness.

Genetic fingerprinting of salmon louse (Lepeophtheirus salmonis) populations in the North-East Atlantic using a random forest classification approach.

Caligid sea lice represent a significant threat to salmonid aquaculture worldwide. Population genetic analyses have consistently shown minimal population genetic structure in North Atlantic Lepeophtheirus salmonis, frustrating efforts to track louse populations and improve targeted control measures. The aim of this study was to test the power of reduced representation library sequencing (IIb-RAD sequencing) coupled with random forest machine learning algorithms to define markers for fine-scale discrimination of louse populations. We identified 1286 robustly supported SNPs among four L. salmonis populations from Ireland, Scotland and Northern Norway. Only weak global structure was observed based on the full SNP dataset. The application of a random forest machine-learning algorithm identified 98 discriminatory SNPs that dramatically improved population assignment, increased global genetic structure and resulted in significant genetic population differentiation. A large proportion of SNPs found to be under directional selection were also identified to be highly discriminatory. Our data suggest that it is possible to discriminate between nearby L. salmonis populations given suitable marker selection approaches, and that such differences might have an adaptive basis. We discuss these data in light of sea lice adaption to anthropogenic and environmental pressures as well as novel approaches to track and predict sea louse dispersal.