Abstract
Salinity is a critical factor determining the impact and establishment of aquatic invasive species. We quantified the functional responses and prey consumption rates of the invasive mud crab Rhithropanopeus harrisii across a salinity gradient to evaluate how low salinity stress influences foraging in the northern Baltic Sea, and found significant differences in both attack rate ( a ) and handling time ( h ) across salinity treatments. Contrary to expectations of reduced feeding efficiency under osmotic stress, crabs in the lowest experimental salinity (2 ppt) exhibited the shortest handling times and highest feeding rates, more than doubling the prey consumption rates observed in the moderate salinity of 6 ppt. Female crabs also demonstrated higher attack rates, shorter handling times, and greater overall prey consumption than males, likely reflecting increased energetic demands during reproduction. These findings contrast with prior studies from southern Baltic populations, which reported reduced feeding performance at low salinities; potential hypotheses behind these results include population-level adaptation or pre-adaptation to local conditions and higher metabolic rates at low salinities due to osmoregulation. Our results indicate that this species is not only tolerant of but may thrive in fresher environments, positioning it well for persistence and expansion under predicted future climate-driven salinity shifts. Rhithropanopeus harrisii ’s high prey consumption capacity at low salinities poses an increasing threat to native benthic invertebrate communities, and female crabs specifically may impose a stronger foraging pressure than males. Our results highlight the salinity tolerance and ecological impact of this invasive predator, emphasizing its potential to alter invertebrate community dynamics in the Baltic Sea ecosystem .