Mader, Lauren2026-07-152026-07-152026-042026-07-15http://hdl.handle.net/1993/39869Ecosystems increasingly harbour multiple invasive species, which can alter ecological interactions that influence their establishment, spread, and impacts on native communities. The recent arrival of the Asian shore crab to Atlantic Canada, where the European green crab has been well-established since the 1950s, provides an opportunity to examine how these invasive species interact during the initial stage of co-invasion in their newly shared range. This study examined their spatial co-occurrence and relative abundance at two sites in Nova Scotia during the summers (July/August) of 2022–2025 (quadrat sampling), along with diet analyses (stomach content) in 2022 and 2023. Follow-up experiments determined whether feeding and diet are altered by the presence of a competitor (alone vs. inter/intra-specific pairings). Both species were found in areas of <0.25 m2. Green crabs were significantly more abundant than shore crabs (a single exception in 2025), indicating that the shore crab is still in the early stage of invasion. Both species are omnivorous generalists, consuming a variety of shared food items (12 species/taxa); however, the relative proportions of food items in crab stomachs differed between species and locations. Animal prey was predominant in green crab stomachs, whereas shore crabs contained a relatively high proportion of macroalgae. Similarly, green crabs were more likely to consume animal prey than macroalgae and vice versa for shore crabs. Green crabs altered their diet in the presence of shore crabs such that when paired with a shore crab, they were equally likely to consume either food item, but when alone or paired with a conspecific, they were more likely to consume barnacles. In contrast, shore crabs did not alter their diet in the presence of green crabs. These results are important for understanding how interactions among invasive species influence feeding and resource use, with implications for population and community dynamics.engEuropean green crabCarcinus maenasAsian shore crabHemigrapsus sanguineusinvasive species