Spatial overlap and trophic interactions between a native commercial crab and the European green crab in Atlantic Patagonia

The European green crab, Carcinus maenas, is a highly invasive species capable of exerting significant impacts on native biota, particularly on species of ecological and/or economic importance. In Atlantic Patagonia, green crabs have been rapidly expanding their distribution along the coast, yet their biotic interactions with native crab species have not been examined. Here, we investigate the agonistic interactions of invasive green crabs with the native commercially important paddle crab (Ovalipes trimaculatus) in Atlantic Patagonia. This study determined spatial overlap between both species and experimentally evaluated predator-prey interactions and competition for food. Our results indicate coexistence of Carcinus and Ovalipes trimaculatus in sandy bottoms of Nuevo Gulf, with green crabs being much more abundant than paddle crabs. Carcinus was present across all sampled locations, exhibiting highly variable abundances and considerable sex ratio disparity. In aquarium trials, mutual predation only occurred between Carcinus and O. trimaculatus of contrasting sizes, although the time taken to observe predation events significantly differed between both species, with green crabs displaying much higher voracity. Additionally, green crabs were the first to hoard food when it was offered. These findings suggest that predation by green crabs especially on juveniles paddle crabs may play a role in the decline of O. trimaculatus in formerly abundant shallow areas in Nuevo Gulf. Thus, this study lays the groundwork for assessing interactions between Carcinus and a broader range of native crab species, aiming to deepen our understanding of current and potential interactions in the SW Atlantic.