An invader chronicles: local ecological niche of Mnemiopsis leidyi in the Venice Lagoon

The invasive ctenophore Mnemiopsis leidyi poses ecological threats in invaded coastal ecosystems such as the Venice Lagoon due to its high fecundity and adaptability to various climates. Although its dynamics have been studied in other regions, information from Mediterranean lagoons, which are characterized by strong spatial and seasonal variability in environmental conditions, remains limited. This study provides the first integrated field and laboratory investigation of the species’ ecological niche in the Venice Lagoon, combining two years of spatial distribution monitoring with controlled experiments to define key environmental thresholds for its survival. Our results shows that the species displays a seasonal pattern, blooming in late spring and late summer-early autumn, likely related to warmer temperatures and optimal salinity; indeed, its abundance positively correlated with water temperature and salinity. The controlled laboratory results integrated field observations by showing that M. leidyi can survive across a wide range of temperatures (10–32 °C) and salinities (10–34), but the extreme conditions of this range, such as very high temperatures (32 °C) or low salinity (10), markedly reduced its survival. By integrating in situ observations with experimentally estimated thresholds, this study provides novel insights into the ecological niche of M. leidyi in a Mediterranean lagoon. The results suggest that ongoing climate change may shift the lagoon towards more favorable conditions for this species, potentially intensifying bloom events and their cascading ecological impacts. These findings highlight the need for targeted monitoring and adaptive management to mitigate the ecological and socio-economic consequences of M. leidyi expansion.