Can marginal aquatic habitats serve as corridors for Procambarus clarkii expansion towards the lagoon and sea waters?

This study investigated the distribution, abundance, and population structure of the invasive Procambarus clarkii in understudied small marginal water bodies along the Venice lagoon. These water bodies comprise expanses of brackish water, shallow freshwater canals, and small ponds, previously constituting part of a fishing valley. The aim was to fill the knowledge gap about the species colonization of these specific environments, analyse its relationships with the aquatic fauna and evaluate whether it could also inhabit coastal environments with increasing salinities. Sampling was conducted using fishing pots in 10 stations, each characterized by distinct environmental characteristics such as salinity, nutrient concentrations, water body width, water flow and floristic cover. The results showed that P. clarkii successfully invaded most of these marginal habitats. Although poor water quality and high nutrient levels do not preclude the presence of this species, they seem to influence its abundance. In contrast, salinity resulted to be a primary factor determining the presence or absence of the species, acting as a physiological barrier, limiting P. clarkii expansion toward more sea-influenced parts of the lagoon coastal environments. Moreover, pH, while not affecting the presence of the species, resulted in affecting the growth rates of individuals. In terms of community dynamics, the native nektonic fauna appears largely replaced by more adaptable non-native species, with P. clarkii likely contributing to this displacement, alongside other impacts. Moreover, although strong direct associations with specific aquatic fauna are limited, evidence suggests reciprocal predation between crayfish and fish during different life stages.