Description: The Asian shore crab Hemigrapsus sanguineus and its congener, the Asian brush-clawed crab H. takanoi, were first found in Europe in 1999 and 1994, respectively. Hemigrapsus sanguineus was initially detected in Le Havre (France) and in the Oosterschelde (The Netherlands). Now it occurs from northern France to the German Wadden Sea. Hemigrapsus takanoi was originally found in La Rochelle (France) and is now established from the Bay of Biscay to the German Wadden Sea. In 2014, a Baltic Sea population was detected in Kiel Fjord (Germany), most likely introduced via the Kiel Canal. Here we summarize the most recent findings on the northern expansion of H. sanguineus and H. takanoi and their competition with the native counterpart, the green shore crab Carcinus maenas. Two population studies in the intertidal areas around the rocky island of Helgoland and the Wadden Sea island of Sylt (Germany) revealed that the three species favor different levels of wave exposure. Our studies presented the highest densities of Hemigrapsus spp. in Europe so far with 144 H. sanguineus m-2 on Helgoland, and more than 200 ind. m-2 of either species on Sylt. The Baltic population of H. takanoi is increasing in Kiel Fjord and adjacent bays. Individuals of H. takanoi were recently found in Wismar Bay, further east along the Baltic coast. In the framework of a citizen-science project, specimen of both species were found at the Swedish west coast, representing the northernmost records in Europe so far. The success of established populations and the continuous extension of the distribution areas suggest that the presence and impact of both Hemigrapsus species on European coasts will significantly increase in the future.

Description: Metabolic regulation, control of gene expression or the evolutionary origin of new proteins are examples of biochemical adaptations that allow organisms to survive within a wide spectrum of environmental conditions. The North Sea shrimp Crangon crangon has high reproduction rates. It is an opportunistic feeder and shows to be well adapted to heterogeneous and variable environmental conditions. Previous studies revealed unusual expression patterns and isoforms of digestive enzymes with a high variability between individuals and between seasons. Such a pronounced variability is not common in other decapod species. The unspecific feeding habits of C. crangon can be seen as an adaptation to a variable environment. This may be supported by the heterogeneity of digestive endopeptidases due to the variability of food sources. Previous studies showed protein polymorphism as a phase in molecular evolution. It represents the first step in the long‐lasting establishment of mutations within populations. The reasons for the unusual heterogeneity of digestive enzymes in C. crangon are not yet clear, but a better understanding of this phenomenon can help to explain the extraordinary performance of C. crangon in a highly variable environment. We obtained the transcriptome of midgut gland tissue from C. crangon, which we used as a basis for gene expression analyses. Additionally, the obtained sequences were analysed for isoforms of the key digestive enzymes. First results indicate that the expression of digestive enzymes in C. crangon follow a similar pattern as previously seen in enzyme activities. Cysteine proteinases seem to have more isoforms participating in the extracellular digestion than serine proteinases. This approach will help to better understand processes that modulate the unique expression pattern of digestive enzymes and biochemical strategies that allow this species to exist in a very variable environment.

Description: Hyperiid amphipods are predatory pelagic crustaceans that are particularly prevalent in high-latitude oceans. Many species are likely to have co-evolved with soft-bodied zooplankton groups such as salps and medusae, using them as substrate, for food, shelter or reproduction. Compared to other pelagic groups, such as fish, euphausiids and soft-bodied zooplankton, hyperiid amphipods are poorly studied especially in terms of their distribution and ecology. Hyperiids of the genus Themisto, comprising seven distinct species, are key players in temperate and cold-water pelagic ecosystems where they reach enormous levels of biomass. In these areas, they are important components of marine food webs, and they are major prey for many commercially important fish and squid stocks. In northern parts of the Southern Ocean, Themisto are so prevalent that they are considered to take on the role that Antarctic krill play further south. Nevertheless, although they are around the same size as krill, and may also occur in swarms, their feeding behaviour and mode of reproduction are completely different, hence their respective impacts on ecosystem structure differ. Themisto are major predators of meso- and macrozooplankton in several major oceanic regions covering shelves to open ocean from the polar regions to the subtropics. Based on a combination of published and unpublished occurrence data, we plot out the distributions of the seven species of Themisto. Further, we consider the different predators that rely on Themisto for a large fraction of their diet, demonstrating their major importance for higher trophic levels such as fish, seabirds and mammals. For instance, T. gaudichaudii in the Southern Ocean comprises a major part of the diets of around 80 different species of squid, fish, seabirds and marine mammals, while T. libellula in the Bering Sea and Greenland waters is a main prey item for commercially exploited fish species. We also consider the ongoing and predicted range expansions of Themisto species in light of environmental changes. In northern high latitudes, sub-Arctic Themisto species are replacing truly Arctic, ice-bound, species. In the Southern Ocean, a range expansion of T. gaudichaudii is expected as water masses warm, impacting higher trophic levels and biogeochemical cycles. We identify the many knowlegde gaps that must be filled in order to evaluate, monitor and predict the ecological shifts that will result from the changing patterns of distribution and abundance of this important pelagic group.

Description: Environmental fluctuations can impose energetic constraints on organisms in terms of food shortage or compensation for metabolic stress. To better understand the biochemical strategies that support adaptive physiological processes in variable environments, we studied the lipid dynamics of the brown shrimp Crangon crangon and the pink shrimp Pandalus montagui by analysing their midgut glands during an annual cycle. Both species have an overlapping distribu- tion range in the southern North Sea, but differ in their habitat preferences, reproductive strate- gies, and life-history traits. C. crangon showed minor total lipid accumulation in their midgut glands, ranging between 14 and 17% of dry mass (DM), dominated by phospholipids. In contrast, P. montagui stored significantly larger amounts of total lipid (47−70% DM, mainly triacylglycer- ols) and showed a distinct seasonal cycle in lipid accumulation with a maximum in summer. Fatty acid trophic markers indicated a wide food spectrum for both species, with higher preferences of P. montagui for microalgae. In C. crangon, feeding preferences were less distinct due the low total lipid levels in the midgut gland. PCA based on fatty acid compositions of both species suggested that C. crangon has a broader dietary spectrum than P. montagui. C. crangon seems to have the capacity to use sufficient energy directly from ingested food to fuel all metabolic requirements, including multiple spawnings, without building up large lipid reserves in the midgut gland. P. montagui, in contrast, relies more on the energy storage function of the midgut gland to over- come food scarcity and to allocate lipids for reproduction.

Description: The crabeater seal (Lobodon carcinophaga) is the most abundant Antarctic seal and inhabits the circumpolar pack ice zone of the Southern Ocean. Until now, information on important environmental factors affecting its distribution as well as on foraging behaviour is limited. In austral summer 1998, 12 crabeater seals of both sexes and different age classes were equipped with satellite-linked dive recorders at Drescher Inlet (72.85°S, 19.26°E), eastern Weddell Sea. To identify suitable habitat conditions within the Weddell Sea, a maximum entropy (Maxent) modelling approach was implemented. The model revealed that the eastern and southern Weddell Sea is especially suitable for crabeater seals. Distance to the continental shelf break and sea ice concentration were the two most important parameters in modelling species distribution throughout the study period. Model predictions demonstrated that crabeater seals showed a dynamic response to their seasonally changing environment emphasized by the favoured sea ice conditions. Crabeater seals utilized ice-free waters substantially, which is potentially explained by the comparatively low sea ice cover of the Weddell Sea during summer 1998. Diving behaviour was characterized by short (〉90 % = 0–4 min) and shallow (〉90 % = 0–51 m) dives. This pattern reflects the typical summer and autumn foraging behaviour of crabeater seals. Both the distribution and foraging behaviour corresponded well with the life history of the Antarctic krill (Euphausia superba), the preferred prey of crabeater seals. In general, predicted suitable habitat conditions were congruent with probable habitats of krill, which emphasizes the strong dependence on their primary prey.

Description: The Asian shore crab Hemigrapsus sanguineus (De Haan, 1853) has recently established populations in the North Sea and now occurs within the native ranges of the green crab Carcinus maenas (Linnaeus, 1758). To determine potential competitive effects and to assess the progress of the invasion, species-specific population characteristics (numerical abundances, biomasses, and size distributions) of the two species around the island of Helgoland (German Bight, southern North Sea) were compared for surveys conducted in 2009 and 2014. Sampling sites were chosen based on accessibility and differed in their topography and wave exposure, which allowed testing for the influence of these factors on the establishment success of H. sanguineus. The numerical abundance and biomass of H. sanguineus increased markedly and approached those of C. maenas in 2014. At a sheltered site, H. sanguineus even outnumbered C. maenas, whereas the converse was observed at a site exposed to strong winds and waves. Although such contrasting abundance patterns between the native and the introduced shore crab may be the result of direct interference, the dominance of H. sanguineus at the sheltered site may also be explained by enhanced larval settling rates caused by odors of conspecifics. The results suggest that the invasion of H. sanguineus has not yet reached its equilibrium, and population abundances in the North Sea are expected to further increase in the future.

Description: The impact of global change forces marine species to acclimatize and adapt to new environmental conditions. Some species already experience environments that represent a challenge due to rapid and partly drastic variations, such as the North Sea. The brown shrimp, Crangon crangon, inhabits the shallow coastal areas of the North Sea. Its high abundance and high reproduction rates make this species an important member of the coastal ecosystem and a valuable target for local fisheries. This shrimp is apparently well prepared to thrive in a highly variable environment. However, it is still unknown, how this species manages to cope with these environmental changes at the metabolic level. Until now it was difficult to obtain the transcriptome of a non-model organism like the brown shrimp. However, next-generation sequencing technologies allow performing inexpensive and rapid transcriptome analyses. Here we report about the first transcriptome of midgut gland tissue from C. crangon, which we used as a basis for seasonal gene expression analyses. The brown shrimp seems to have the capability to express specific digestive enzymes depending on different seasonal requirements. Furthermore, C. crangon exhibits an extraordinary enzyme polymorphism, which may suggest a process of molecular evolution. Assuming that polymorphic expression of digestive enzymes is an adaptation to variable environmental conditions, the pronounced enzyme polymorphism observed in C. crangon may reflect an acute adaptive process of an organism coping with a changing environment.

Description: High latitude marine ecosystems are characterized by strong seasonality in incoming light and thus primary production and food availability. Polar zooplankton organisms have developed the ability of storing large amounts of lipid reserves to face this variable environment. Lipids are composed of fatty acids, which are transferred from unicellular algae via zooplankton to higher trophic levels. In our experiments, a 13C labeled diatom-flagellate mix was fed to key zooplankton species (copepods and thecosome pteropods) over some days to a couple of weeks to follow the fatty acid carbon assimilation and possible de novo synthesis of fatty acids and alcohols. Fatty acid and fatty alcohol compositions were determined by gas chromatography. The 13C incorporation was monitored using compound specific isotope ratio mass spectrometry. Among the small sized copepods Pseudocalanus minutus and Oithona similis, maximum lipid turnover occurred in P. minutus, which exchanged 2.6% day-1 of total lipid, whereas 0.5% day-1 were exchanged in O. similis. In P. minutus, the diatom markers 16:1(n-7), 16:2(n-4), and 16:3(n-4) were almost completely renewed from the diet within 21 days, while 15% of the flagellate markers 18:2(n-6), 18:3(n-3) and 18:4 (n-3) were exchanged. In O. similis, 15% of both flagellate and diatom markers were renewed within 21 days. Thecosome pteropods, in contrast, are less lipid-rich and less studied, although they can contribute with more than 20% to the zooplankton biomass in Arctic waters. The daily turnover rate of lipid was between 0.15% day-1 in L. helicina and 1.3% day-1 in L. retroversa. High carbon assimilation was found in both diatom and flagellate markers in L. helicina accounting for 0.8% over 6 days. In L. retroversa, 0.8% of the diatom markers were exchanged after 6 days while 13.9% were renewed in flagellate markers. Our methods allow us to estimate lipid and fatty acid turnover rates of specific Arctic key organisms to better understand the carbon und energy flux through the high latitude marine ecosystems.

Description: Hemigrapsus sanguineus, the Asian shore crab, is a successful invader at the U.S. east coast and the European Atlantic coast, where populations are established from France to Germany. Numerous studies on behavioral aspects and population development are available, however, physiology and energetic impact of the invader on its ecosystem are virtually unknown. We measured respiration rates of H. sanguineus and its native equivalent, the European shore crab C. maenas, from the island of Helgoland, North Sea, Germany. Measurements were conducted at 5, 10, 15 and 20 °C, using a flow-through system. Specific respiration rates were overall similar for both species. Rates increased with temperature and decreased with the mass of the crab. Mass-standardized data revealed that small H. sanguineus showed significantly higher respiration rates at higher temperatures than C. maenas. This difference vanished with increasing crab size. Statistical modelling was used to develop species-specific equations to calculate a crab´s respiration rate in relation to its mass and the ambient temperature. Taking the overall biomass and temperature into account, the population respiration, carbon uptake and the metabolic energy demand, a measure for the population´s ecosystem impact, was calculated. In the Helgoland intertidal, total biomass of H. sanguineus is now about 59% of that of the C. maenas population but the cumulative metabolic energy demand represents already 78% of the value for C. maenas. With still increasing abundances of H. sanguineus and globally rising temperatures, the ecosystem impact of this invader will increase in the future.

Description: The region of the Filchner Outflow System (FOS) in the southeastern Weddell Sea is characterized by intensive and complex interactions of different water masses. Dense Ice Shelf Water (ISW) emerging from beneath the ice shelf cavities on the continental shelf, meets Modified Warm Deep Water (MWDW) originating from the Antarctic Circumpolar Current at the sill of the Filchner Trough. These hydrographic features convert the FOS into an oceanographic key region, which may also show enhanced biological productivity and corresponding aggregations of marine top predators. In this context, six adult Weddell seals (Leptonychotes weddellii) were instrumented with CTD-combined satellite relay data loggers in austral summer 2014. By means of these long-term data loggers we aimed at investigating the influence of environmental conditions on the seals’ foraging behaviour throughout seasons, focussing on the local oceanographic features. Weddell seals performed pelagic and demersal dives, mainly on the continental shelf, where they presumably exploited the abundant bentho-pelagic fish fauna. Diurnal and seasonal variations in light availability affected foraging activities. MWDW was associated with increased foraging effort. However, we observed differences in movements and habitat use between two different groups of Weddell seals. Seals tagged in the pack ice of the FOS focussed their foraging activities to the western and, partly, eastern flank of the Filchner Trough, which coincides with inflow pathways of MWDW. In contrast, Weddell seals tagged on the coastal fast ice exhibited typical central-place foraging and utilized resources close to their colony. High foraging effort in MWDW and high utilization of areas associated with an inflow of MWDW raise questions on the underlying biological features. This emphasizes the importance of further interdisciplinary ecological investigations in the near future, as the FOS may soon be impacted by predicted climatic changes.