Description: Copepods comprise the majority of mesozooplankton communities in all marine regions. Their diversity is likely regulated by environmental parameters and species-specific ecophysiological aspects making the distributional pattern of certain species an environmental indicator to detect changes in the marine habitat. We studied copepod distribution and diversity at six stations along a meridional transect in the eastern Atlantic Ocean (25°N to 21°S) from surface to 2000 m depths. Community and trophic structures with special regard to calanoid copepods were analyzed. Below the euphotic zone, representatives of the family Spinocalanidae were particularly abundant and diverse but morphological species identification both of adults and juveniles was very challenging. To elucidate both diversity and species- and stage-specific vertical distribution of Spinocalanidae we therefore applied an integrated taxonomic approach combining morphology, DNA sequence analyses and proteomics using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Each specimen was analysed by the three methodologies by portioning the whole organism. Species clusters were similar for DNA sequence analyses and MALDI-TOF MS and resulted in a higher amount of species clusters compared to the morphological identification. Since MALDI-TOF MS is a rather time- and cost-efficient technology, we were able to identify high individual numbers of the Spinocalanidae and received a quantitative, high species-resolution picture of adult and juvenile Spinocalanidae and their distributional patterns.

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: The Asian shore crab H. sanguineus first appeared at the French coast in the late 1990’s. It rapidly extended its range further north to the German Wadden Sea and recently to western Sweden. In the intertidal area, it co-occurs with the European green crab C. maenas. As the ecophysiology of H. sanguineus is virtually unknown, the physiological capacities of both species and their potential for intra-guild competition were investigated. The aim of this study was to specifically compare the energy deposition and dietary preferences of ovigerous females of both species. Females of H. sanguineus and C. maenas carrying immature or mature eggs were collected in April, June, August and October 2015 in an intertidal area of the Island of Helgoland, North Sea. Total lipid levels and fatty acid compositions were determined of both midgut glands and eggs. In H. sanguineus, total lipid levels of the midgut glands were clearly higher than those of C. maenas (40% vs. 10% dry mass, DM). Immature eggs were quite lipid-rich in both species with 30% and 25%DM, respectively, whereas in mature eggs, lipid levels decreased to ~15%DM each. A Principal Component Analysis of the fatty acid compositions of midgut glands and eggs revealed separate clusters for both species with C. maenas lipids more characterized by membrane fatty acids. In C. maenas fatty acids of midgut glands and eggs clustered together largely dominated by carnivory biomarkers. Fatty acids of midgut glands and all eggs of H. sanguineus formed separate clusters and trophic markers indicate a more herbivorous diet. Higher lipid levels and thus more pronounced energy deposition in H. sanguineus midgut glands indicate higher starvation tolerance for females, a potential competitive advantage over C. maenas. Direct food competition, however, seems negligible, as H. sanguineus prefers a more herbivorous diet than C. maenas. Deviating fatty acid compositions in H. sanguineus midgut glands and eggs suggest that this species may represent an income breeder, utilizing energy from both the midgut gland but also from dietary input. Most brachyuran crabs are capital breeders, which rely exclusively on internal reserves.

Description: Biological invasions can entail major threats to marine biodiversity. Non-indigenous species may induce changes in community structure and ecosystem functioning, thereby affecting ecosystem services and human economic interest and health. Decapod brachyuran crabs are among the most invasive marine animal taxa. The originally European species Carcinus maenas and the Asian shore crab Hemigrapsus sanguineus invaded different coastal areas around the world. While their invasion history and ecology has been thoroughly investigated, physiological properties of H. sanguineus are virtually unknown. The aim of this study was to compare the metabolic energy demand of both crab species and - based on these data - to assess their potential dietary impact on the ecosystem. Respiration measurements were conducted with a flow-through system covering a temperature range naturally experienced by these crabs (5, 10, 15 and 20 °C). Both species were analyzed on the island of Helgoland in April, June and August 2015. A general linear mixed-effects model (LMM) was applied to test for the effects of species, temperature, biomass and sex on respiration rates. Overall rates increased with temperature but decreased with the mass of the crabs. Respiration rates did not differ significantly between sexes in both species. From the full model, two separated LMMs were created for either species. They allowed establishing species-specific equations for the prediction of respiration rates y (nmol d-1 g-1) for a crab of any given mass xMass (g) at any given ambient temperature xTemp (°C): ln y = 10.39 + (-0.34 * ln xMass) + (0.06 * xTemp) for C. maenas and ln y = 10.42 + (-0.39 * ln xMass) + (0.08 * xTemp) for H. sanguineus. The mass-specific respiration rates of C. maenas and H. sanguineus were quite similar. By applying the diet-dependent respiratory quotient, oxygen uptake may be used to calculate carbon uptake and metabolic energy demand either for single crabs or for entire populations of a given area. On the population level, the metabolic energy demand and thus ecosystem impact of both species depend primarily on their abundance in the field and, less so on their dietary preferences.

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: This study aimed at understanding how life-cycle strategies of the primarily herbivorous Pseudocalanus minutus and the omnivorous Oithona similis are reflected by their lipid carbon turnover capacities. The copepods were collected in Billefjorden, Svalbard, and fed with 13C labeled flagellates and diatoms during 3 weeks. Fatty acid (FA) and fatty alcohol compositions were determined by gas chromatography, 13C incorporation was monitored using isotope ratio mass spectrometry. Maximum lipid turnover occurred in P. minutus, which exchanged 54.4% of total lipid, whereas 9.4% 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. P. minutus exhibited typical physiological adaptations of herbivorous copepod species, with a very high lipid turnover rate and the ability to integrate FAs more rapidly from diatoms than from flagellates. O. similis depended much less on lipid reserves and had a lower lipid turnover rate, but was able to ingest and/or assimilate lipids with the same intensity from various food sources, to sustain shorter periods of food shortage.

Description: The intertidal Asian shore crab H. sanguineus was initially found on the French coast in the late 1990’s. It rapidly extended its range further north and is now well established in the German Wadden Sea. Recently, it was also found in western Sweden. In its intertidal habitat, it co-occurs with the European green crab C. maenas. The ecophysiology of H. sanguineus is virtually unknown. In this study, the physiological capacities of both species and their potential for intra-guild competition were investigated. We specifically compared the energy deposition and dietary preferences of ovigerous females of both species. Females of both species carrying immature or mature eggs were collected in April, June, August and October 2015 in an intertidal site on the Island of Helgoland, North Sea, Germany. Total lipid levels of midgut glands and eggs were acquired via extraction. Subsequently, fatty acid compositions were determined through gas chromatography. Total lipid levels of H. sanguineus midgut glands were clearly higher than those of C. maenas (40% vs. 10% dry mass, DM). Immature eggs of both species were quite lipid-rich with 30% and 25%DM, respectively. In mature eggs, lipid levels decreased to ~15%DM each. A Principal Component Analysis of the fatty acid compositions of midgut glands and eggs revealed separate clusters for both species. Lipids of C. maenas were characterized more by membrane fatty acids. Fatty acids of C. maenas midgut glands and eggs clustered together. They were largely dominated by carnivory biomarkers. Contrastingly, fatty acids of midgut glands and all eggs of H. sanguineus formed separate clusters and trophic markers indicated a more herbivorous diet. Higher lipid levels and thus more pronounced energy deposition in H. sanguineus midgut glands indicate higher starvation tolerance for females, a potential competitive advantage over C. maenas. Direct food competition, however, seems negligible, as H. sanguineus prefers a more herbivorous diet than C. maenas. Deviating fatty acid compositions among H. sanguineus midgut glands and eggs suggests that this species may represent an income breeder, utilizing energy from both the midgut gland and dietary input. In contrast, most brachyuran crabs are capital breeders, relying exclusively on internal reserves.