Multispecies coexistence of invasive alien crayfish in the north-western Italian lakes

Invasive alien species are worldwide recognized as one of the top drivers of species loss, negatively affecting local economy, ecosystem services and human well-being. The risk of spreading of aquatic invasive species (AIS) and environmental distress is most likely to increase with the upward trend of extreme weather events such as severe floods and prolonged droughts. Among AIS, crayfish appear to exacerbate already the highly uncertain ecological responses of the vulnerable freshwater ecosystems to abrupt environmental changes. Recently, three north-western Italian lakes (Maggiore, Mergozzo and Orta) are under investigation because they are invaded by three non-native crayfish species: the spiny-cheek crayfish Faxonius limosus (Rafinesque, 1817), the American signal crayfish Pacifastacus leniusculus Dana, 1852, and the red swamp crayfish Procambarus clarkii (Girard, 1852). While the first species is so far diffused in all the three lakes and coexists together with P. clarkii in lake Maggiore and lake Orta, P. leniusculus is still recorded only in the Swiss part of Lake Maggiore. Our study is focused on the monitoring of the distribution and coexistence of the invasive crayfish species recorded along the littoral zone of two lakes (Mergozzo and Orta) during a twoyear (2021-2022) survey. The studied period was marked by extremly prolonged droughts in the Northern Italy. Monthly dynamics, morphological traits, together with sex/age ratio of the crayfish species and how they differ interspecifically were discussed. Intraspecific variability of morphological traits were also analysed considering dissimilarities in the freshwater habitats (lakes).