Icelandic Fisheries Laboratories

Young igneous geothermal systems recharge by magmatic activity. Due to Iceland’s location on the mid-ocean ridge, repeated dyking compensates here for the spreading. This study examines the impact of intrusive and eruptive events on the thermal evolution of the Krafla geothermal system. The so-called “Krafla fires” in 1975-84 were a volcanic episode comprising 20 intrusive and eruptive events, during which seven of them intersected the geothermal system.The effects of repeated dyking on temperature, pressure, and enthalpy, as well as steam content, are modelled in simple 2D profiles with HYDROTHERM (USGS). Calculating a heat budget can help to exploit geothermal energy sustainably: How much energy is inputted by the dykes into the geothermal system? How much of this heat is lost to the atmosphere by advection and conduction? How fast is heat transferred in the subsurface?The total heat input of the dyke into the geothermal system is 0.5-1 x 1018 J. During, and shortly after the eruptive episode, the dyke nearly cools down to the ambient temperatures of the system. Models and previous analyses of steam clouds in air photos indicate that around 10 % of the heat is lost from the surface to the atmosphere, mostly in the first weeks/months after the dyking event, while 90 % of the dyke’s energy is dissipated into the geothermal reservoir. As the system is already close to the boiling point, the additional heat input by the dyke, leads to steam generation, which rises in the high-permeable lava-hyaloclastite layer. It collects below the clay cap and rises through fissures and fractures. In the lower permeable layer of basement intrusions, the steam is less mobile and stays in the vicinity of the dyke. The main changes in temperature and pressure can be observed in the two-phase and superheated steam regions, where enthalpy increases strongly compared to the initial setting. Long-term simulations indicate that the heat input by the dykes formed in the Krafla fires remains in the reservoir for at least several decades and plays a critical role in maintaining the geothermal system.

Density-dependent competition for food influences the foraging behaviour and demography of colonial animals, but how this influence varies across a species’ latitudinal range is poorly understood. Here we used satellite tracking from 21 Northern Gannet Morus bassanus colonies (39% of colonies worldwide, supporting 73% of the global population) during chick-rearing to test how foraging trip characteristics (distance and duration) covary with colony size (138–60 953 breeding pairs) and latitude across 89% of their latitudinal range (46.81–71.23° N). Tracking data for 1118 individuals showed that foraging trip duration and maximum distance both increased with square-root colony size. Foraging effort also varied between years for the same colony, consistent with a link to environmental variability. Trip duration and maximum distance also decreased with latitude, after controlling for colony size. Our results are consistent with density-dependent reduction in prey availability influencing colony size and reveal reduced competition at the poleward range margin. This provides a mechanism for rapid population growth at northern colonies and, therefore, a poleward shift in response to environmental change. Further work is required to understand when and how colonial animals deplete nearby prey, along with the positive and negative effects of social foraging behaviour.

Abstract Unstable conditions are commonly encountered during industrial storage and transportation of frozen fish. Temperature stress and fluctuations may increase the amount of unfrozen water in the muscle and enzymatic activity and lipid oxidation can thus still take place during frozen storage. The aim of this study was to investigate the changes of characteristics of different muscle types of herring at unstable modelled conditions during storage and transportation. Compositional changes, lipid oxidation and lipid hydrolysis were monitored in light and dark muscle of Atlantic herring (Clupea harengus), during frozen storage, as affected by temperature stress (samples were stored at − 25 °C for 2 months, then stressed at − 12 °C for 1 month, followed by storage at a stable − 25 °C for the remaining storage duration), and compared to samples stored at a stable − 25 °C for 14 months. The dark muscle was more sensitive to lipid oxidation than the light muscle, leading to faster degradation. Increased lipid oxidation and lipid hydrolysis were observed in temperature‐stressed samples of both muscle types. The study demonstrated the importance of avoiding temperature stress during industrial frozen storage and transportation to improve the quality and shelf life of frozen herring products. Removal of dark muscle by deep skinning could benefit both processors and customers regarding the shelf life and nutritional value of the light herring muscle.

A central question at the interface of food-web and climate change research is how secondary production, or the formation of heterotroph biomass over time, will respond to rising temperatures. The metabolic theory of ecology (MTE) hypothesizes the temperature-invariance of secondary production, driven by matched and opposed forces that reduce biomass of heterotrophs while increasing their biomass turnover rate (production : biomass, or P:B) with warming. To test this prediction at the whole community level, we used a geothermal heat exchanger to experimentally warm a stream in southwest Iceland by 3.8°C for two years. We quantified invertebrate community biomass, production, and P : B in the experimental stream and a reference stream for one year prior to warming and two years during warming. As predicted, warming had a neutral effect on community production, but this result was not driven by opposing effects on community biomass and P:B. Instead, warming had a positive effect on both the biomass and production of larger-bodied, slower-growing taxa (e.g., larval black flies, dipteran predators, snails) and a negative effect on small-bodied taxa with relatively high growth rates (e.g., ostracods, larval chironomids). We attribute these divergent responses to differences in thermal preference between small- vs. large-bodied taxa. Although metabolic demand vs. resource supply must ultimately constrain community production, our results highlight the potential for idiosyncratic community responses to warming, driven by variation in thermal preference and body size within regional species pools.

Stream ecology may be influenced by the temporary trapping of solutes in geomorphologic structures, which is usually quantified by fitting the Transient Storage Model to tracer data. This paper explores the relationships between the parameters of this model and those of two simpler models, namely the Advection-Dispersion Model and the Aggregated Dead Zone model. It is motivated by the possibility of obtaining more reliable transient storage parameter values by correlating them with the parameters of the other models instead of evaluating them directly. Results were obtained by fitting all three models to a set of tracer data from mountain streams, predominantly in Iceland. Some strong correlations were found between some of the parameters of the transient storage model and the advection-dispersion model, but no strong correlations were found between the parameters of the transient storage model and the aggregated dead zone model. For all three models, combinations of the optimized parameters correctly described the bulk movement of the solute cloud, giving confidence in the optimized parameters.

Streams within geothermal areas in Iceland that vary in a syndrome of temperature-linked variables, including discharge and potential grazing pressure (snails vs. chironomid larvae), provided a test of how microvegetation structure might change systematically with such drivers. We examined if such streams could form a parallel with biome sequences, for example with similar change in overall structure and organism traits found from tundra to Boreal forest. The warmer streams had an over-story of bryophytes with more open patches of epilithic algae and Cyanobacteria, and a grazer community of snails and blackfly larvae; the vegetation of the colder streams consisted mainly of epilithic algae and Cyanobacteria, dominated by grazing chironomid larvae. Diatom species comprising the epilithic assemblages were generally smaller in the warmer streams compared with the colder streams. Temperature and discharge did not significantly influence the diversity of diatoms (Shannon Index, Sørensen Index, Evenness, Species richness), although more species were observed in the colder streams compared with the warmer streams. Trait diversity was greatest in the coldest streams, but despite high grazing pressure only one growth form (attachment by a mucilage stalk) was predominant in the warmer regimes. Grazers may have influenced diatom species traits but did not significantly suppress the diatom biomass. Analogy with the sequence from tundra, through taiga to boreal forest, over a comparable temperature gradient, showed some parallel features but important differences. Microorganism systems may thus not always be the useful surrogates for larger systems that some ecologists have suggested.

Investigating patterns of genetic variation in hybridizing species provides an opportunity to understand the impact of natural selection on intraspecific genetic variability and interspecific gene exchange. The Atlantic eels Anguilla rostrata and A. anguilla each occupy a large heterogeneous habitat upon which natural selection could differentially shape genetic variation. They also produce viable hybrids only found in Iceland. However, the possible footprint of natural selection on patterns of genetic variation within species and introgressive hybridization in Icelandic eels has never been assessed. We revisited amplified fragment length polymorphism data collected previously using population genomics and admixture analyses to test if (i) genetic variation could be influenced by non-neutral mechanisms at both the intra- and interspecific levels, and if (ii) selection could shape the spatio-temporal distribution of Icelandic hybrids. We first found candidate loci for directional selection within both species. Spatial distributions of allelic frequencies displayed by some of these loci were possibly related with the geographical patterns of life-history traits in A. rostrata, and could have been shaped by natural selection associated with an environmental gradient along European coasts in A. anguilla. Second, we identified outlier loci at the interspecific level. Non-neutral introgression was strongly suggested for some of these loci. We detected a locus at which typical A. rostrata allele hardly crossed the species genetic barrier, whereas three other loci showed accelerated patterns of introgression into A. anguilla in Iceland. Moreover, the level of introgression at these three loci increased from the glass eel to the yellow eel stage, supporting the hypothesis that differential survival of admixed genotypes partly explains the spatio-temporal pattern of hybrid abundance previously documented in Iceland.

The influence of different cooling techniques (dry ice/ice packs) and storage temperature (-2°C/3°C) to prolong the shelf life of Arctic charr (Salvelinus alpinus) fillets were evaluated by sensory analysis, physical methods, chemical and microbial analysis. The effects of storage temperature were stronger than of different cooling agents. Superchilling (-2°C) of fillets packed with dry ice resulted in 6 days extension of shelf life compared to chilling (3°C). The use of dry ice parallel to superchilling prolonged shelf life for 1 day compared to fillets stored with ice packs. No negative effects on quality of the fillets where detected that could be linked to cell destruction caused by partial freezing or to sour taste, caused by absorption of CO2 gas in fish flesh.