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: Since 1999, the invasive Asian shore crab Hemigrapsus sanguineus successfully established populations along the Atlantic coastline of Europe, now reaching from the French Channel coast to the German Bight. While various studies on population development and behavior are available, the physiology of H. sanguineus and its energetic impact on the habitat are virtually unknown. We measured the oxygen consumption of H. sanguineus and of its native equivalent, the European shore crab Carcinus maenas, and assessed the energetic ecosystem impact of the invader versus the native species. Respiration rates were determined in a flow-through system at 5, 10, 15 and 20 °C, the crab´s natural temperature range in European habitats. We compared mass-specific respiration rates of mass-standardized crabs of 0.5, 5 and 10 g body mass. Small H. sanguineus specimens consumed significantly more oxygen at higher temperatures than small C. maenas. This difference was less distinct in medium-sized animals and absent in larger animals. We established species-specific models to calculate respiration rates for a crab using the individual´s biomass and the water temperature. These models were applied to the crab populations from the intertidal of the island of Helgoland (Germany) based on data from August 2014. While total population biomass of H. sanguineus was as high as 59% of that of C. maenas, population respiration and energy demand of the invader reached about 78% relative to the value for the native species. As H. sanguineus abundances are still rising, the food uptake and thus the energetic ecosystem impact of this invader will continuously increase in the future.

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: Accurate species identification is crucial for ecological studies. For copepods, this is usually based on a few diagnostic morphological characters, which can be highly conserved, resulting in an underestimation of species diversity in many copepod families. We elucidate species richness in the morphologically challenging and ecologically important deep-sea copepod family Spinocalanidae in the tropical Atlantic by applying an integrated taxonomic approach combining morphology, DNA-sequence analyses and proteomic fingerprinting. In total, 28 morphospecies could be discriminated, while 39 putative species were detected using DNA-sequence analyses and 42 using proteomic fingerprinting. This outcome verifies proteomic fingerprinting to simplify and accelerate future biodiversity studies of copepods with high taxonomic resolution. Our findings demonstrate the power of this integrated morphological and molecular taxonomic approach by revealing high numbers of cryptic or pseudocryptic species and thus uncovering the incompleteness of taxonomic guides for this group in the poorly explored mesopelagic realm. Furthermore, our analyses reveal a close relationship of Mospicalanus and Spinocalanus group A and indicate that the genus Spinocalanus may be polyphyletic. The underestimated species diversity suggests complex ecological interactions in terms of predator–prey relationships, interspecific competition and species-specific specializations in the vast, but under-studied mesopelagic realm.

Description: The physiology of the successful intertidal invader, the Asian shore crab Hemigrapsus sanguineus, is essentially unknown. It is quite abundant from France to German coasts but information on food preferences, energy storage and breeding strategy are still lacking. Hemigrapsus sanguineus and its native ecological equivalent, the European green crab Carcinus maenas, were collected in April, June, August and October 2016 in the intertidal area of the island of Helgoland, North Sea, Germany. Midgut glands were dissected and in case of ovigerous females, additionally the egg masses were sampled. Lipids were extracted and the fatty acid composition was determined by gas chromatography. The lipid contents of H. sanguineus midgut glands was higher and more variable over the seasons than those of C. maenas (20 - 60% vs. ~20%, respectively). Trophic marker fatty acids revealed a more herbivorous diet of H. sanguineus, whereas C. maenas profiles suggested a wide range from more herbivorous to more carnivorous diets. The fatty acid compositions of eggs and midgut glands formed two separate clusters in H. sanguineus but both tissue types were similar in C. maenas. Hemigrapsus sanguineus stored much more energy than C. maenas and may cope better with longer periods of starvation. The invaders were able to build up and maintain these reserves by utilizing mostly low quality algal food. Further, H. sanguineus is an income breeder, utilizing recently eaten food for reproduction, whereas C. maenas is a capital breeder. The physiological properties suggest that the invader is competitively superior over the native crab.

Description: The brown shrimp, Crangon crangon, has high reproduction rates, is an opportunistic feeder on endo and epibenthic organisms, and is apparently well adapted to variable environmental conditions. Previous studies revealed unusual expression patterns of digestive endopeptidases with high variability between individuals and between seasons. Such a pronounced variability is not common in other decapod species. The reasons for the heterogeneity of digestive enzymes in C. crangon are not yet clear, but it may help to explain the extraordinary performance of C. crangon in a highly variable environment. We established a transcriptome-based expression analysis of anabolic and catabolic digestive key enzymes of C. crangon to compare gene expression rates with enzyme activities. Additionally, detailed sequence analyses will be applied to identify multiple gene products. First results indicate that specific enzymes, particularly trypsin and triacylglycerol lipase, are differentially expressed. Statistical analyses suggest that only a minority of the assayed shrimp exhibit high expression levels of enzyme transcripts, whereas most individuals show low expression rates confirming heterogeneity of digestive enzyme transcription. The strategy of integrated gene expression and protein analyses will elucidate biochemical strategies, which support adaptive physiological processes of C. crangon in a highly variable and seasonally changing environment.