The Impacts of Invasive Crayfish and Other Non-Native Species on Native Freshwater Crayfish: A Review

Freshwater crayfish are vital species in ecosystems where they naturally occur, as they hold keystone and ecological engineering positions in these systems. Non-native species are common and widely spread throughout Earth's freshwater ecosystems and can have severe impacts on native crayfish populations. There has yet to be a comprehensive global review of the impacts of non-native species on native crayfish. Two literature searches were conducted using Web of Science and Google Scholar to find articles to address four key aims: (1) summarise trends in the literature; (2) examine the mechanisms by which invasive crayfish impact native crayfish species; (3) examine the mechanisms by which other non-native species, such as fish, impact native crayfish species; and (4) identify gaps in knowledge and research priorities. This review highlights that a far greater amount of research has addressed the effects of invasive crayfish than other non-native species. The research on invasive crayfish focuses on four types of interactions with native crayfish: competition, predation, introduction of disease, and reproductive impacts. Studies addressing the impacts of other non-native species on crayfish indicate that predation and habitat destruction by these species are the key processes impacting native crayfish. It is evident that field-based research, particularly concerning competition between invasive and native crayfish, is limited. Therefore, further in situ research is needed to assess the validity of laboratory results in a natural setting. Additionally, in many cases, the impact of certain non-native species on native crayfish populations has gone unmonitored. For this reason, it is recommended that additional research focus on assessing the impact of these non-native species. To conclude, the impacts of invasive crayfish on native crayfish are profound and wide-ranging, often leading to population decline or extirpation. Further, other non-native species are also likely to have a highly deleterious impact on native crayfish populations; however, more research is required to understand the scope of this impact.