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: 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.