Description: Euphausiid (krill) and amphipod dynamics were studied during 2006–2011 by use of plankton nets in Kongsfjorden (79�N) and adjacent waters, also including limited sampling in Isfjorden (78�N) and Rijpfjorden (80�N). The objectives of the study were to assess how variations in physical characteristics across fjord systems affect the distribution and abundance of euphausiids and amphipods and the potential for these macrozooplankton species to reproduce in these waters. The abundances of euphausiids and amphipods were higher in Kongsfjorden than in Rijpfjorden and Isfjorden, and the highest abundances were observed at the innermost stations of Kongsfjorden, where Thysanoessa inermis and Themisto libellula dominated. The Atlantic species Thysanoessa longicaudata, Meganyctiphanes norvegica and Themisto abyssorum dominated at the outside Kongsfjorden. Inter-annual and seasonal variability in abundances of euphausiids and amphipods were evident. The presence of ripe euphausiids outside Kongsfjorden indicates that they may reproduce in these areas. Mature individuals of T. abyssorum were recorded mainly outside Kongsfjorden, whereas no mature or ripe T. libellula were present in both the inner and outer parts of this fjord. If the warming trend persists, as seen during the last decade, this would favour the Atlantic/boreal euphausiid species, while Arctic species, such as the amphipod T. libellula, may decline. Euphausiids and amphipods are major food of capelin (Mallotus villosus) and polar cod (Boreogadus saida), respectively, in this region, and changes in prey abundance will likely have an impact on the feeding dynamics of these important fish species.

Description: Variability in upwelling events may lead to periods of constrained food availability in the northern Benguela upwelling system (NBUS), thereby affecting the physiological state and metabolic activity of euphausiids. Most attention has so far been paid to seasonal effects but little is known about regional variability.Metabolic activity (expressed by respiration and excretion rates) and physiological state (expressed by reproductive effort and moult activity) in Euphausia hanseni were examined at different stations during austral summer (minimum upwelling) and austral winter (maximum upwelling). Overall, regional differences in physiological state, influencing metabolic activity, were greater than seasonal ones, indicating favourable conditions for growth and reproduction year-round. Higher respiration rateswere found for females in more advanced stages of sexual development.Moult stage did not affect oxygen consumption rates, however. The physiological state of E. hanseni at the time of capture may serve as ameaningful indicator of the associated hydrographic conditions in the NBUS,to be further used in eco-system analysis on seasonal or long-term time scales. A latitudinal comparison of species highlights the extraordinary physiological plasticity of euphausiids.

Description: Modern Oxygen Minimum Zones (OMZs) are extensive and prevail in most of the world oceans. Anthropogenic and climate induced changes will cause OMZs to expand, while coastal hypoxia is assumed to increase in extent and severity. Particularly in Eastern Boundary Upwelling Ecosystems (EBUEs), such as the Humboldt and the Benguela upwelling system, severe OMZs prevail. Animals living in these areas have to physiologically and/or behaviourally adapt to the low oxygen levels or will be excluded from these areas or at least their vertical distribution ranges will be limited. It is assumed that some areas may experience a shift from an abundant and diverse regime to one that is lean and dominated by vertical migrators. Further, temperature is known to impact the hypoxia tolerance of animals negatively. Euphausiids are known as pronounced diel vertical migrators, thus facing different levels of oxygen and temperature within 12 hours and are an important trophic link between primary producers and higher trophic levels throughout the world oceans. The critical oxygen pressure (Pcrit) and the regulation index (RI), as a method to differentiate between oxygen conformity and regulation, were used to assess hypoxia tolerances of different species from different ecosystems. Furthermore, diel vertical migration behaviour was monitored in some species. We will present and compare hypoxia tolerances of different dominant euphausiids species, show how oxygen availability may affect their vertical migration behaviour and assess how future climate scenarios (warming waters and decreasing oxygen content) may alter horizontal and/or vertical distribution of these species.

Description: Das interdisziplinäre GENUS-Projekt (Geochemistry and Ecology of the Namibian Upwelling System) ist ein vom BMBF gefördertes Verbundprojekt mit dem Ziel den Zusammenhang zwischen Klimavariabilität, biogeochemischen Stoffkreisläufen und der Ökosystemstruktur des nördlichen Benguelagebietes besser zu verstehen. Ein Schwerpunkt des GENUS-Projektes liegt dabei auf der Quantifizierung des aktiven Kohlenstoffflusses durch die vorherrschenden Zooplanktonarten. Das Benguelaauftriebsgebiet vor der Küste Namibias gehört zu den produktivsten Meeresgebieten weltweit und hat somit einen starken ökonomischen Einfluss auf die Anrainerstaaten und versorgt diese mit wichtigen marinen Ressourcen (Fische, Krebstiere u.a.). Im nördlichen Benguelagebiet wird das Zooplankton ganzjährig von Copepoden, Dekapoden und verschiedenen Krillarten dominiert. Viele dieser Planktonorganismen unternehmen ausgeprägte Vertikalwanderungen und transportieren dadurch Kohlenstoff, den sie während der Nacht in den oberen Wasserschichten als Nahrung aufgenommen haben, aktiv in tiefere Wasserschichten. In der Tiefe wird die Nahrung katabolisiert und der Kohlenstoff als anorganischer Kohlenstoff über die Atmung wieder ausgeschieden. Dabei ist sowohl die Horizontalverteilung des Planktons, als auch deren Wanderungsverhalten von verschiedenen biotischen und abiotischen Parametern beeinflusst. Einerseits, wahrscheinlich bedingt durch hydrographische und topographische Unterschiede, ist die Planktonbiomasse im nördlichen Bereich des Untersuchungsgebietes deutlich höher als im südlichen Bereich. Andererseits passen einzelne Arten ihr Vertikalwanderungsverhalten, d.h. die Wanderungsamplitude, an die vorherrschenden hydrographischen Bedingungen, vor allem Temperatur und Sauerstoffverfügbarkeit, an. Dies führt zu einer hohen räumlichen Variabilität in den aktiven Kohlenstoffflüssen. Zusätzlich führen Unterschiede in den Habitatpräferenzen (Schelf/Schelfhang/Offener Ozean) dazu, dass der aktive Kohlenstofftransport auf dem Schelf maßgeblich von Copepoden und einer Krillart bestimmt wird, wohingegen am Schelfhang und im offenen Ozean Krill und Dekapoden diesen Prozess dominieren. Vergleiche der aktiven mit den passiven Kohlenstoffflüssen (mittels Sedimentfallen) zeigen, dass das Zooplankton über dem Schelf in etwa 1-8% des organischen Kohlenstoffflusses ausmacht, wohingegen sie 7-73% zu den Flüssen im Hangbereich und offenen Ozean beitragen. Analysen des Einflusses der Temperatur und Sauerstoffverfügbarkeit auf das Verhalten und die Physiologie der Tiere legen dabei nahe, dass klimatische Veränderungen in den Meeresregionen auch den Beitrag des Planktons zu den Kohlenstoffflüssen regional, aber auch im globalen Maßstab, signifikant verändern werden.

Description: Polar environments like the high Arctic Kongsfjord are characterized by pronounced seasonality leading to strong variations in primary production. Food sources are particularly scarce during winter. Herbivorous krill, such as the arcto-boreal Thysanoessa inermis are key components in the ecosystem of Kongsfjord and strongly rely on phytoplankton as a food source. Therefore, during polar night such species must be adapted to survive long periods without significant nutritional input. We investigated physiological mechanisms and the allocation of energy resources to try to explain how T. inermis manages to survive the Arctic winter. Adult specimens caught in late summer were kept under starvation conditions for 28 days. Changes in metabolic rates (respiration and excretion) and biochemical composition (protein, lipid and fatty acid analyses) were monitored. In contrast to the Antarctic krill, Euphausia superba, and the subtropical E. hanseni, the arcto-boreal species did not reduce metabolism but utilized lipid reserves for survival. Assessed from total lipid stores and energy demand, the potential survival period was estimated at 63 days without food uptake, which is not sufficient to survive the entire winter. Results were compared to specimens that overwintered in-situ and discussed in relation to other euphausiids. In conclusion, T. inermis is well adapted to survive the Arctic winter provided that alternative food sources are available, but has a different strategy to cope with starvation than krill species from other latitudes.

Description: There is growing interest in using recirculating aquaculture systems (RAS) to raise noble crayfish Astacus astacus a valuable and once plentiful food species in Europe, now a highly endangered species. The growth and survival of A. astacus was compared in growth trials in RAS and open-pond systems (OPS) over a period of 2 months. Energy and lipid content of available diets and crayfish tissue were also determined. Growth of A. astacus during summer was significantly (p 〈 0.01, one sample t test) higher in OPS (SGR 1.23) than in RAS even at the highest feeding ration provided at 5 % bw/d−1 (RAS HI SGR 0.78 ± 0.06). OPS crayfish also had significantly (p 〈 0.01 OPS vs. all RAS treatments; Pairwise Wilcoxon) higher lipid content (8.51 %) than RAS crayfish (RAS HI 5.73 %, RAS MED 6.93 %, RAS LOW 5.92 %). Survival rates in RAS were, however, 100 % compared with previous observations in OPS of approx. 70 %. While results showed OPS growth exceeds than that in RAS in the short term, RAS survival rates and annualized growth performance may outweigh this disadvantage, particularly if optimal artificial diets for RAS holding are provided. Feed and crayfish analysis indicated that culturing A. astacus in RAS require a diet protein content exceeding 30 % and lipid content of 〈13 %, indicating that the carp diet supplied was not optimal. RAS culture allows this valuable species to be cultured in controlled, disease-free enclosed systems—resulting in high-value food products as well as high-quality seedlings for restocking purpose.

Description: Our study deals with the lipid biochemistry of the krill community in the ecosystem of the high Arctic Kongsfjord (Svalbard). During the last decades, Kongsfjord experienced a change in krill species composition due to recent increased advection of Atlantic water masses carrying characteristic boreal as well as subtropical-boreal euphausiids into the ecosystem. The lipid biochemistry and trophic relationships of the species recently inhabiting the Arctic water masses are scarcely known, although a change in a krill population may have a significant impact on the ecosystem. A comparison of nutrition and energy storage strategies, stable isotopes, lipid profiles and fatty acid compositions showed remarkable differences between the krill species. These reflected the diverse feeding behaviours and specific adaptations to the environments of their origin: the boreal Meganyctiphanes norvegica and subtropical Nematoscelis megalops appear more carnivorous, have significantly lower mean lipid contents (29 % and 10 %, respectively) and a different energy storage pattern (triacylglycerols and polar lipids, respectively) than the arcto-boreal Thysanoessa inermis, which consists of up to 54 % of lipids mainly stored as wax esters (〉 40 %). These differences may have significant implications for the rapidly changing marine food-web of Kongsfjord - especially for higher trophic levels relying on the nutritional input of animal lipids.

Description: Two fjords in West Spitsbergen (Hornsund 77°N and Kongsfjorden 79°N) differ with regard to their exposure towards increasingly warm Atlantic water inflow. Hornsund remains in many respects cooler than Kongsfjorden (on average 2°C SST in summer) and is less influenced by warmer and more saline Atlantic waters. Reported changes in the physical environment (temperature rise, freshwater inflow, salinity drop, turbidity, fast-ice reduction, coastal change) are discussed in the context of biological observations in the pelagic and benthic realms with special reference to krill (Euphausiacea). We conclude that well-documented changes in the physical environment have had little effect on the fjord biota and that both organisms and their ecological functions in the fjords are well adapted to the scale of ongoing change. The observed changes fit the definition of ecosystem maturation, with greater diversity, a more complex food web and dispersed energy flow at the warmer site.

Description: Recent studies have indicated a metabolic temperature sensitivity in both the arcto-boreal krill species Thysanoessa inermis and Thysanoessa raschii that may determine these species' abundance and population persistence at lower latitudes (up to 40° N). T. inermis currently dominates the krill community in the Barents Sea and in the high Arctic Kongsfjord. We aimed to increase the knowledge on the upper thermal limit found in the latter species by estimating the CT50 value (19.7 °C) (critical temperature at which 50 % of animals are reactive) and by linking metabolic rate measurements with molecular approaches. Optical oxygen sensors were used to measure respiration rates in steps of 2 °C (from 0 to 16 °C). To follow the temperature-mediated mechanisms of passive response, i.e., as a proxy for molecular stress, molecular chaperone heat shock protein 70 (Hsp70) sequences were extracted from a transcriptome assembly, and the gene expression kinetics were monitored during an acute temperature exposure to 6 or 10 °C with subsequent recovery at 4 °C. Our results showed upregulation of hsp70 genes, especially the structurally constitutive and mitochondrial isoforms. These findings confirmed the temperature sensitivity of T. inermis and showed that the thermal stress took place before reaching the upper temperature limit estimated by respirometry at 12 °C. This study provides a baseline for further investigations into the thermal tolerances of arcto-boreal Thysanoessa spp. and comparisons with other krill species under different climatic regimes, especially Antarctica.