Description: Marine biological invasions can have alarming and devastating ecological and economic, impacts on biodiversity, ecosystem balance, fisheries and tourism. Due to global change, the number of bioinvasions has severely increased over the last decades. Although, range expansion and the invasion of non-native habitats by marine and terrestrial species have occurred naturally since the existence of life, the rate of human-mediated translocations of species as a consequence of expanded worldwide trade, shipping and aquaculture activities has, however, never been larger and will further massively increase in the near future. For the marine environment, it is estimated that, only in ballast water of ships, approximately 10,000 species per day are transported around the globe. Most of these potential invaders fail, but a few survive, establish and spread in their new environment. To control and prevent invasions, it is of high importance to understand the mechanisms and traits determining the success of invasive species. One of the crucial factors, especially in the early stages of an invasion process, is stress tolerance i.e. the ability to maintain fitness under adverse conditions. Studies comparing the performance of invasive species in their invasive range to native species showed that the invasive species performed better in the majority of cases. In this case, stress tolerance can be considered a species-specific trait. Additionally, some studies comparing the performance of native and invasive populations of the same species were conducted with terrestrial plants and revealed higher competiveness in the invasive plant populations. The marine environment however seems to be nearly unexplored with regard to worldwide intraspecific comparisons of stress tolerance. The aim of this study is to compare the performance of native and invasive populations of successful marine invaders under different abiotic stressors. Laboratory experiments with three marine benthic cosmopolitan invaders in four different biogeographic regions were conducted to detect possible differences in stress tolerance between native and invasive populations. Native and invasive populations of adults and juvenile Pacific oysters, Crassostrea gigas, were exposed to hypoxia and heat stress. Juveniles were additionally exposed to hyposalinity stress. Furthermore, a native and invasive population of the vase tunicate, Ciona intestinalis, were exposed to hypoxia and heat stress and native as well as invasive populations of the green alga, Codium fragile, were exposed to heat and hyposalinity stress. Survival (C. gigas, C. intestinalis) or the 6 maximum quantum yield (C. fragile) under stressful conditions was measured and the native and invasive populations of each species were compared. A second experiment attempted to detect effects of stress history. It was tested whether previously stressed groups of Crassostrea gigas or Ciona intestinalis were more stress tolerant towards a subsequent stressor of another quality than previously unstressed groups. The stress history experiment revealed no significant differences between previously stressed and previously unstressed individuals within both species. Invasive populations of adult Crassostrea gigas from the German Wadden Sea as well as juveniles from Guernsey were significantly more tolerant to hypoxia stress (1 mg l-1) than the native population from Japan. An invasive Japanese population of Ciona intestinalis was significantly more tolerant towards hypoxia stress when compared to the native population from Wales. The same pattern was found for Codium fragile comparing invasive (Chile) and native populations (Japan) under heat stress while under hyposalinity stress an inverse pattern was revealed. The native population (Japan) of juvenile of C. gigas was also more tolerant towards heat stress than its invasive population from Guernsey. Insignificant bidirectional differences in stress tolerance were found between the native (Japan) and invasive (USA) populations of juvenile C. gigas in hyposaline and hypoxic conditions. This study shows, in four out of six significant comparisons, higher stress tolerance is found in invasive populations compared to native populations of the same species. Hence, stress tolerance should not only be considered species-specific but also a population-specific trait. These population-specific differences can be either a consequence of selection of stress-tolerant genotypes during transport or of interactions with the biotic and abiotic environment in the target area after introduction.