The Asian shore crab Hemigrapsus sanguineus was initially introduced to the French Atlantic coast in the late 1990´s. Since then it has successfully established persistent populations along the European Atlantic coasts propagating further north. The invasive crab was found in the German part of the Wadden Sea for the first time in 2007 and at Helgoland in 2008. There, it now shares its intertidal habitat with the native European green crab Carcinus maenas. In order to test for potential interspecific effects between these two ecological equivalents, we analysed populations of both species in the rocky intertidal of the island of Helgoland (German Bight, North Sea) in 2009 and 2014. Numbers of animals and their biomasses of both species from four sites around the island were recorded. Although mean abundances of H. sanguineus around Helgoland more than doubled from 2009 to 2014, they were still lower than the abundances of C. maenas, which were similar between the years. In contrast, mean biomass of C. maenas slightly decreased from 2009 to 2014, while values for H. sanguineus increased almost sevenfold. Differences between sites may be due to differences in local habitat characteristics such as topography, algae coverage, wave exposure, and/or predation risk. Nonetheless, the results showed that both species co-occur and reproduce in the rocky intertidal of Helgoland, providing no clear evidence for a displacement of either species.