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: Hyperiid amphipod crustaceans are abundant in Southern Ocean waters from the Polar Frontal Zone to shelf waters where they represent a major prey for fish and seabirds. Hyperiella dilatata has evolved a peculiar anti-predatory behaviour: it abducts chemically-protected, shell-less pteropods from the water column and carries them on their dorsal side, holding it between its pereopods (McClintock & Janssen, 1990). The pteropod Clione antarctica produces de novo a predator-deterrent chemical named pteroenone (Bryan et al., 1995). Tandem pairs of pteropods and amphipods were significantly less predated upon than single individuals of Hyperiella and hence this behaviour is very efficient as protection from visually hunting icefish in the crystal-clear shelf waters around the continent (McClintock & Janssen, 1990), however, in the open ocean this behaviour was so far undocumented. We report this association at four different open-water sites in the Southern Ocean between 45 and 71°S and develop hypotheses on its origin and function. H. dilatata abducted Spongiobranchaea pteropods in the Polar Frontal Zone and Clione further south in the Weddell Sea. Lengths of the abducted pteropods varied greatly; the biggest pteropod carried was around half the host’s size. Molecular barcodes of both host and pteropods were obtained. Finally, we hypothesize against which potential predators this anti-predatory behaviour may have been selected for.