Abstract
Non-native invasive species threaten freshwater biodiversity and ecosystem services (ES), which are critical for environmental health and possess noteworthy socioeconomic and cultural importance. This research specifically delves into the impact of the signal crayfish (Pacifastacus leniusculus) in a protected area (Montesinho Natural Park, Portugal). It combines scientific inquiry with local ecological knowledge (LEK) to elucidate the implications of this non-native invasive species for biodiversity and ES across five river basins. Data was collected through face-to-face interviews with 132 residents from villages adjacent to these rivers, maintaining a balanced representation of both genders. Approximately 46% of the males and 25.5% of the females reported sightings of the signal crayfish, describing initial introductions around 8 and 5.8 years ago, respectively. The majority (78.6% of men and 80% of women) believed that the crayfish populations have since burgeoned. Respondents evaluated the crayfish's ES impact on a 0-5 scale, with 5 being the most significant. Both genders recognized the impacts on different ES, such as riverbank erosion (1.5), food sources for humans (2.5) and other species (3.8), water quality (3.3), pest regulation (3), habitat provision (3.9), and recreational and tourism activities (2.8). Both men (87.5%) and women (77.8%) identified fish, specifically brown trout (Salmo trutta), as the most affected taxonomic group by this non-native invasive species. Unanimously, participants concurred on the importance of integrating LEK with scientific research to improve invasive species management. The findings emphasize the urgent need for robust scientific study and targeted management actions considering the perceived detrimental negative impacts of signal crayfish. It suggests the crucial role of local communities in knowledge generation and response formulation, thus reinforcing our collective efforts to safeguard biodiversity and ES amidst invasive species threats.