Trophic Niche Overlap Between the Invasive Crab <i>Rhithropanopeus harrisii</i> (Gould, 1841) and Native Crab Species in the Southwest Atlantic Coast

ABSTRACT The introduction of exotic species is one of the main drivers of biodiversity loss in aquatic ecosystems. The Harris mud crab Rhithropanopeus harrisii , native to the Atlantic coast of North America, was recorded in the Patos Lagoon estuary (southern Brazil) in the 1980s, likely introduced via ballast water. However, the effects of this invader on the native fauna were never evaluated. This study assessed the natural diet and trophic niche overlap between the invader and four native crab species ( Cyrtograpsus angulatus , Callinectes sapidus , Neohelice granulata , and Panopeus austrobesus ) along a salinity gradient in the estuary. Multivariate analyses were performed to identify dietary differences among species and sites, and the Morisita–Horn index was applied to estimate trophic overlap. Callinectes sapidus , Panopeus austrobesus , and Rhithropanopeus harrisii exhibited generalist feeding habits, consuming mollusks, crustaceans, polychaetas, plant material, and detritus, whereas Neohelice granulata showed a predominantly herbivorous diet, and Cyrtograpsus angulatus displayed trophic plasticity by alternating between animal and plant items. Significant differences in diet composition were observed among species, with low overall trophic overlap. The highest overlap was observed between Callinectes sapidus and Panopeus austrobesus , whereas the lowest overlap occurred between Neohelice granulata and Rhithropanopeus harrisii . Despite its generalist feeding behavior, Rhithropanopeus harrisii appears not to compete strongly with native species, likely exploiting unoccupied niches or using shared resources differently. The invader's high trophic plasticity may enhance its establishment in the estuary, while low overlap suggests niche differentiation or resource partitioning with native crabs.