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Adult Euphausia superba survive winter without or with little feeding. It is not exactly known whether the scarcity of food or an internal clock, set by the natural Antarctic light regime, are responsible for non-feeding. Our research questions were therefore the following: (1) How will physiological and biochemical conditions of krill change during long-term starvation at constant light regime? (2) If and how do enzyme activities change during such starvation? (3) What is the influence of food availability versus that of light regime? To answer these questions, adult krill were starved under laboratory conditions for 12 weeks with constant light regime (12:12; dark/light) and the impact on physiological functions was studied. Initial experimental condition of krill resembled the condition of late spring krill in the field with fully active metabolism and low lipid reserves. Metabolic activity and activities of enzymes catabolising lipids decreased after the onset of starvation and remained low throughout, whereas lipid reserves declined and lipid composition changed. Mass and size of krill decreased while the inter-moult period increased. Depletion of storage- and structural metabolites occurred in the order of depot lipids and glycogen reserves after onset of starvation until proteins were almost exclusively used after 6–7 weeks of starvation. Results confirmed various proposed overwintering mechanisms such as metabolic slowdown, slow growth or shrinkage and use of lipid reserves. However, these changes were set in motion by food shortage only, i.e.without the trigger of a changing light regime.

Euphausiids constitute a major biomass component in shelf ecosystems and play a fundamental role in the rapid vertical transport of carbon from the ocean surface to the deeper layers during their daily vertical migration (DVM). DVM depth and migration patterns depend on oceanographic conditions with respect to temperature, light and oxygen availability at depth, factors that are highly dependent on season in most marine regions. Here we introduce a global krill respiration ANN (artificial neural network) model including the effect of latitude (LAT), the day of the year (DoY), and the number of daylight hours (DLh), in addition to the basal variables that determine ectothermal oxygen consumption (temperature, body mass and depth). The newly implemented parameters link space and time in terms of season and photoperiod to krill respiration. The ANN model showed a better fit (r2 = 0.780) when DLh and LAT were included, indicating a decrease in respiration with increasing LAT and decreasing DLh. We therefore propose DLh as a potential variable to consider when building physiological models for both hemispheres. For single Euphausiid species investigated in a large range of DLh and DoY, we also tested the standard respiration rate for seasonality with Multiple Linear Regression (MLR) and General Additive model (GAM). GAM successfully integrated DLh (r2 = 0.563) and DoY (r2 = 0.572) effects on respiration rates of the Antarctic krill, Euphausia superba, yielding the minimum metabolic activity in mid-June and the maximum at the end of December. We could not detect DLh or DoY effects in the North Pacific krill Euphausia pacifica, and our findings for the North Atlantic krill Meganyctiphanes norvegica remained inconclusive because of insufficient seasonal data coverage. We strongly encourage comparative respiration measurements of worldwide Euphausiid key species at different seasons to improve accuracy in ecosystem modeling.

We investigate how individual growth and population structure of Antarctic krill (Euphausia superba) would be affected by changes in the spatio-temporal dynamics of the sea ice cover. This is of high interest since krill has adapted to a particular environmental regime which is likely to change dramatically over the coming years. The response of krill will in particular depend on its chronobiology: when and why does krill, after a period of decreased metabolic activity during winter, switch back to an active metabolic state? If this switch is purely triggered by the Zeitgeber day length, the metabolically active period of krill and the availability of food resources would become out of phase with potentially drastic consequences for krill populations. Alternatively, the switch might also be triggered by food availability. To explore the consequences of different environmental scenarios and assumptions about krill chronobiology, we developed a spatially explicit individual-based simulation model. The model operates on a daily time step. Each time step ice cover extent and day length for each grid cell in the model are updated. In the model demographic and behavioural processes are simulated every time step. Particularly all modelled krill individuals grow depending on food availability, move, reproduce given their reproductive and metabolic state, and die with a certain probability. Growth and reproduction are modelled according to a simplified version of dynamic energy budget theory (DEBKiss). Simulations run for several years until quasi-stationary population characteristics have emerged. Population metrics such as length distribution and heterogeneity in reproductive state within the population are observed. We will present the model and demonstrate its potential by contrasting results for selected environmental and chronobiological scenarios. The model’s design and implementation are open so that suggestions regarding alternative assumptions and scenarios can eas

During evolution, a wide range of organisms from cyanobacteria to humans have adapted to the day-night cycle, caused by the earth’s rotational movements, by developing an endogenous timing system – a circadian clock – that allows synchronization of metabolism, physiology and behaviour with the environment and that also may modulate seasonal responses. Our current molecular understanding of biological rhythms and clocks is largely restricted to circadian and seasonal rhythms in land model species such as the fruit fly, the mouse or the thale cress. In marine organisms in general, little is known about the principles of endogenous clocks and how these clocks interact with environmental cycles. Marine ecosystems are currently experiencing rapid anthropogenic climatic changes. In particular, polar and sub-polar latitudes comprise the fastest warming regions on the planet with profound impacts on the marine environment. I will outline the importance of this research field in polar regions on the Southern Ocean key species Antarctic krill, Euphausia superba. Our seasonal investigations on krill, both field based and in the laboratory, revealed that important physiological functions such as metabolic activity, feeding and growth, as well as maturity are affected by different light-dark cycles, irrespective of food supply, suggesting that the photoperiod acts as the main Zeitgeber for these annual cycles. In recent investigations we identified an endogenous timing system, which is synchronized by the seasonal cycle of photoperiod, and its link to metabolic key processes. We will further outline the implication of these findings for krill stocks in a changing environment and will present a recently started 5 years project on clocks and rhythms in polar pelagic organisms.

A declining trend of Antarctic Krill biomass has be documented in concert with an decrease in winter sea ice duration in the Atlantic sector of the Southern Ocean since the mid seventies, suggesting that larval krill development during winter might be a key factor to understand the stock development of krill. Correlative studies make us aware that krill might be sensitive to environmental changes but cannot answer the question why. Therefore our goal was to go beyond collative studies towards a mechanistic understanding between larval krill and sea ice to understand which winter sea ice condition might favour larval krill development and hence recruitment success of krill. During two dive camps, established on an ice floe (9 and 14 days respectively), as well as two zodiac dives, we did an intense under ice survey on larval distribution and abundance in relation to under ice topography and biomass as well as larvae behaviour. In the presentation, Prof. Bettina Meyer will give an overview of the diving operations and show first results of the winter expedition in the Northern Weddell Sea in 2013.

Das Leben im und unter dem Eis der Polarmeere gibt uns noch immer viele Rätsel auf- wir bezeichnen eisige Lebensräume als „extrem" und wundem uns über die besonderen Anpassungen von Mikroorganismen, Pflanzen und Tieren sowie einiger menschlicher Kulturen an die gefrorene Umwelt. Die ersten Polarforscher riskierten ihr Lehen, um in die eisigen Weiten vorzudringen. Mittlerweile, scheint eher der Mensch die Natur als die Natur den Menschen zue drohen. Das Eis der Polarregionen - besonders der Arktis - schwindet durch die globale Erwärmung we- sentlich schneller als vorhergesagt. Die Zukunß der eishedeckten Lebensräume und ihrer Bewohner ist ungewiss.

Ring artifacts appear in computed tomography images if there are too large inhomogeneities between different detector elements. The question of how large inhomogeneities are acceptable is gaining in importance due to the development of energy discriminating photon counting CT, where detector homogeneity is an important design parameter. We propose using the systematic-to-statistical error quotient q, defined as the variance of the expected log-normalized count number between detector elements (dels) divided by the variance of log-normalized count numbers measured with the same del, as a metric of ring artifact visibility. With a simple observer study using simulated images, it is shown that rings are visible in the reconstructed image if q exceeds a threshold which lies close to 1.2·10 -3 for 1500 detector elements and 2000 projection angles. It is also shown by visual inspection of simulated images that the threshold value is, to a good approximation, inversely proportional to the number of angle measurements and independent of the number of detector elements. The results suggest that a simple oberver study, together with these scaling relationships, is sufficient for establishing sinogram homogeneity requirements for a particular reconstruction method., QC 20120621

Antarctic krill Euphausia superba (hereafter ‘krill’) occur in regions undergoing rapid environmental change, particularly loss of winter sea ice. During recent years, harvesting of krill has increased, possibly enhancing stress on krill and Antarctic ecosystems. Here we review the overall impact of climate change on krill and Antarctic ecosystems, discuss implications for an ecosystem-based fisheries management approach and identify critical knowledge gaps. Sea ice decline, ocean warming and other environmental stressors act in concert to modify the abundance, distribution and life cycle of krill. Although some of these changes can have positive effects on krill, their cumulative impact is most likely negative. Recruitment, driven largely by the winter survival of larval krill, is probably the population parameter most susceptible to climate change. Predicting changes to krill populations is urgent, because they will seriously impact Antarctic ecosystems. Such predictions, however, are complicated by an intense inter-annual variability in recruitment success and krill abundance. To improve the responsiveness of the ecosystem-based management approach adopted by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR), critical knowledge gaps need to be filled. In addition to a better understanding of the factors influencing recruitment, management will require a better understanding of the resilience and the genetic plasticity of krill life stages, and a quantitative understanding of under-ice and benthic habitat use. Current precautionary management measures of CCAMLR should be maintained until a better understanding of these processes has been achieved.

Der Dienstwagen zur privaten Nutzung ist eine der häufigsten Nebenleistungen zum regulären Einkommen in Deutschland. Die sehr günstige steuerliche Behandlung dieses geldwerten Vorteils trägt wesentlich zur Attraktivität dieses Bezahlungsmodells bei. Die vorliegende Studie wurde im Auftrag des Bundesumweltministeriums erstellt. Sie untersucht den deutschen Firmenwagenmarkt und die Besteuerung aus ökonomischer und rechtlicher Perspektive. Als Folge der faktischen Subventionierung werden mehr als 50 Prozent aller neuen Pkw als Firmenwagen zugelassen, also rund 750.000 Fahrzeuge im Jahr. Insgesamt sind ungefähr 2,5 Mio. der Pkw in Deutschland privat mitgenutzte Firmenwagen. Die Analysen zeigen, dass die untersuchten Regeln die größte Steuervergünstigung in Deutschland darstellen – auch wenn sie offiziell nicht in dieser Liste auftauchen. Neben starken Verzerrungen in der Konsumwahl und Wahl des Transportmittels gehen umfangreiche Treibhausgasemissionen auf das Konto dieser Steuersubvention. Schließlich hat das Steuerprivileg auch einen deutlichen regressiven Charakter, d.h. die Subventionshöhe steigt mit dem Einkommen der Begünstigten. Die Studie diskutiert zahlreiche Reformmodelle. Der abschließende Implementierungsvorschlag zielt auf eine Neutralität, in der Gestellung eines Firmenwagens und monetäres Einkommen steuerlich gleich behandelt werden. Diese Reform würde die Subventionen in Steuern und Sozialabgaben um 3,3 bis 5,5 Mrd. Euro reduzieren. Insgesamt ließe sich zwischen 2012 und 2020 eine Reduzierung der CO2-Emissionenum 2,9 bis 5,7 Mio. Tonnen erreichen.

A major aim of this review is to determine which physiological functions are adopted by adults and larvae to survive the winter season with low food supply and their relative importance. A second aim is to clarify the extent to which seasonal variation in larval and adult krill physiology is mediated by environmental factors with a strong seasonality, such as food supply or day light. Experimental studies on adult krill have demonstrated that speciWc physiological adaptations during autumn and winter, such as reduced metabolic rates and feeding activity, are not caused simply by the scarcity of food, as was previously assumed. These adaptations appear to be inXuenced by the local light regime. The physiological functions that larval krill adopt during winter (reduced metabolism, delayed development, lipid utilisation, and variable growth rates) are, in contrast to the adults, under direct control by the available food supply. During winter, the adults often seem to have little association with sea ice (at least until early spring). The larvae, however, feed within sea ice but mainly on the grazers of the ice algal community rather than on the algae themselves. In this respect, a miss-match in timing of the occurrence of the last phytoplankton blooms in autumn and the start of the sea ice formation, as has been increasingly observed in the west Antarctic Peninsula (WAP) region, will impact larval krill development during winter in terms of food supply and consequently the krill stock in this region.

Antarctic krill, Euphausia superba, shapes the structure of the Southern Ocean ecosystem. Its central position in the food web, the ongoing environmental changes due to climatic warming, and increasing commercial interest on this species emphasize the urgency of understanding the adaptability of krill to its environment. Krill has evolved rhythmic physiological and behavioral functions which are synchronized with the daily and seasonal cycles of the complex Southern Ocean ecosystem. The mechanisms, however, leading to these rhythms are essentially unknown. Here, we show that krill possesses an endogenous circadian clock that governs metabolic and physiological output rhythms. We found that expression of the canonical clock gene cry2 was highly rhythmic both in a light-dark cycle and in constant darkness. We detected a remarkable short circadian period, which we interpret as a special feature of the krill's circadian clock that helps to entrain the circadian system to the extreme range of photoperiods krill is exposed to throughout the year. Furthermore, we found that important key metabolic enzymes of krill showed bimodal circadian oscillations (~9–12 h period) in transcript abundance and enzymatic activity. Oxygen consumption of krill showed ~9–12 h oscillations that correlated with the temporal activity profile of key enzymes of aerobic energy metabolism. Our results demonstrate the first report of an endogenous circadian timing system in Antarctic krill and its likely link to metabolic key processes. Krill's circadian clock may not only be critical for synchronization to the solar day but also for the control of seasonal events. This study provides a powerful basis for the investigation into the mechanisms of temporal synchronization in this marine key species and will also lead to the first comprehensive analyses of the circadian clock of a polar marine organism through the entire photoperiodic cycle.