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 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.

Description: Adult Euphausia superba survive winter without or with little feeding. It is not exactly known whether the scarcity of food or an internal clock, set by the natural Antarctic light regime, are responsible for non-feeding. Our research questions were therefore the following: (1) How will physiological and biochemical conditions of krill change during long-term starvation at constant light regime? (2) If and how do enzyme activities change during such starvation? (3) What is the influence of food availability versus that of light regime? To answer these questions, adult krill were starved under laboratory conditions for 12 weeks with constant light regime (12:12; dark/light) and the impact on physiological functions was studied. Initial experimental condition of krill resembled the condition of late spring krill in the field with fully active metabolism and low lipid reserves. Metabolic activity and activities of enzymes catabolising lipids decreased after the onset of starvation and remained low throughout, whereas lipid reserves declined and lipid composition changed. Mass and size of krill decreased while the inter-moult period increased. Depletion of storage- and structural metabolites occurred in the order of depot lipids and glycogen reserves after onset of starvation until proteins were almost exclusively used after 6–7 weeks of starvation. Results confirmed various proposed overwintering mechanisms such as metabolic slowdown, slow growth or shrinkage and use of lipid reserves. However, these changes were set in motion by food shortage only, i.e.without the trigger of a changing light regime.