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 brown shrimp Crangon crangon is a key component of the North Atlantic coastal food web and an important target species for the fishery economy. As the brown shrimp contains large amounts of protein and essential fatty acids, its consumption makes it a beneficial choice for humans. Commercially harvested crustaceans like C. crangon are frequently affected by bacterial shell disease, with necrotizing erosions and ulcerations of the cuticle. To determine whether shell disease influences the nutritional value of C. crangon, total protein and lipid contents, as well as fatty acid compositions of muscle tissue and hepatopancreas, together with the hepatosomatic index, were examined in healthy and affected individuals. The biochemical composition of the tissues did not differ significantly between the 2 groups. Also, the hepatosomatic index, as an indicator of energy reserves in shrimps, was similar between healthy and affected animals. Our results indicate that the nutritional value of C. crangon is not affected by shell disease, as long as it remains superficial as in the present study.

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 invasive Asian shore crab Hemigrapsus sanguineus and the native European green crab Carcinus maenas share intertidal habitats along European North Atlantic shores and may compete for food. We evaluated the energy-storing capacities of the 2 species and determined their dietary preferences by means of lipid analysis and fatty acid trophic marker indices. Specimens of both sexes and various sizes were sampled in the rocky intertidal of the island of Helgoland (North Sea) in April, June, August, and October 2015. Total lipids of the midgut glands were significantly higher in H. sanguineus than in C. maenas and followed a distinct seasonal cycle in both sexes (ca. 20−50% of dry mass, DM). The lower lipid contents of C. maenas (ca. 20% of DM) remained at a similar level throughout the seasons. The seasonal differences in the females of H. sanguineus may be due to higher reproductive output and, consequently, lipid turnover, but remain unexplained in males. Trophic indices for Bacillariophyceae, Chlorophyta, and especially Phaeophyceae were higher in H. sanguineus than in C. maenas, suggesting a higher degree of herbivory of the invader. In contrast, the Rhodophyta index was higher in C. maenas. Thus, competition for food between the 2 species will probably be low in habitats rich in macroalgae. The ability of H. sanguineus to utilize mainly energy-poor algae but accumulate high-energy reserves may be an advantage for successfully establishing persistent populations in new habitats.