The western Pacific crabs Hemigrapsus takanoi and H. sanguineus were first introduced to Europe in the 1990s and have afterwards spread along the coast of the European Wadden Sea (south-eastern North Sea) between 2005 and 2010. The crab fauna in the intertidal zone of the Wadden Sea was formerly dominated by the European Shore Crab Carcinus maenas, itself being a successful invader in many coastal regions around the world and well known as a strong competitor. Therefore, the rapid establishment of Hemigrapsus spp. was very surprising. We hypothesized that timing of crab recruitment and subsequent growth of the cohorts play an important role to explain the success of both Hemigrapsus species. Since December 2014, a bi-weekly survey on the recruitment of all three crab species is conducted in the northern Wadden Sea. To our knowledge, this is the first temporally highly resolved, long-running data series on the recruitment of Hemigrapsus spp. for Europe. First results of the survey provide evidence that recruitment phases of C. maenas and Hemigrapsus spp. are temporally shifted against each other, leading to consequences on interactions between the species. We will present the survey data, along with experimental results on competition and predation among juvenile crabs.