MULTI-CRASH: Multi-dimensional ecological cascades triggered by an invasive species in pristine habitats

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Invasive dynamics of the signal crayfish Pacifastacus leniusculus in a protected area

Publication . Carvalho, Francisco; Alves, Henrique; Pascoal, Cláudia; Castro, Paulo; Miranda, Fernando Jorge Veloso; Teixeira, Amílcar; Cássio, Fernanda; Sousa, Ronaldo

Invasive species have been drivers of biodiversity loss and functional changes in aquatic ecosystems, including in protected areas. Therefore, monitoring population invasion dynamics and biological traits is fundamental to better understand their ecological and economic impacts and for management actions development. We followed signal crayfish (Pacifastacus leniusculus) invasion in Rabaçal River upper reach at Montesinho Natural Park, Portugal. We collected information on the spread and biological traits (abundance, size, weight, physical condition, sex ratio, and aggressiveness) to assess differences between invasion core and front areas and among years. Signal crayfish population remained restricted since first reports in 2013 in the invasion core until 2017. After 2019, signal crayfish population has been spreading downstream, decreasing abundance at invasion core but increasing at invasion front. Significant higher number of crayfish with claw loss indicate potential higher signs of aggressiveness in the invasion front. Results also demonstrate a significant dominance of females although sex ratio is closer to 1:1 at the invasion front. Overall, results indicate signal crayfish is spreading and increasing their abundance at Rabaçal River highlighting the need for immediate management actions to hold dispersion and mitigate possible impacts.

2024Journal article

Open access

Intrapopulation differences in biological traits and impacts in a highly invasive freshwater species

Publication . Alves, Henrique; Gonçalves, Diana; Nogueira, António Barbosa; Teixeira, Amilcar; Padilha, Janeide; Sousa, Ronaldo

Individual variation assessments are essential to better understand population and community dynamics, as well ecosystem functioning. Although researchers have long recognized this aspect, only recently has evidence accumulated about the ecological importance of variation within species. The incorporation of individual variation provides an even more complete description of the effects a species may have on ecosystems and this detailed ecological knowledge can be especially important in the context of biological invasions. In this study, we used an invasion gradient of the signal crayfish Pacifastacus leniusculus in the Rabaçal River (NE Portugal) to assess possible intrapopulation differences in key biological traits and evaluate possible changes in ecological impacts. For this, we collected individuals from the core and front of an invasion gradient to characterize several traits such as abundance, size, sex-ratio, body condition, behaviour (i.e. boldness), and trophic niche. In addition, we performed two laboratory experiments to assess possible differences regarding the consumption of prey (gastropods), leaf mass loss, and nutrients release. Signal crayfish from the front of the invasion gradient have lower abundance, are larger, predominantly male, have better body condition in both sexes, exhibit increased boldness, and have higher δ 15 N and lower δ 13 C values. In addition, in experimental conditions, signal crayfish from the front of the invasion gradient consumed more gastropods and leaves and increased the concentration of nitrates and phosphates in the water. Overall, the signal crayfish has different biological traits and distinct ecological impacts along the invasion gradient in the studied river. Our study demonstrates the relevance of assessing biological traits and impacts of invasive species at the intrapopulation level.

2025Journal article

Open access

Subtle ecological effects of the invasive signal crayfish (Pacifastacus leniusculus) on Iberian fish communities

Publication . Oliveira, Bruno; Nogueira, António B.; Teixeira, Amilcar; Sousa, Ronaldo

The introduction of non-native species can disrupt the structure of communities and affect the functioning of freshwater ecosystems, disturbing various taxonomic groups, including fish. This study aimed to assess the ecological effects of the recent introduction of the signal crayfish Pacifastacus leniusculus in the fish communities in the Rabaçal and Tuela River basins (Montesinho Natural Park and adjacent areas; NE of Portugal), an area with very low human disturbance. A total of 34 sites (18 invaded and 16 non-invaded) were sampled in the summer of 2022 and comparisons were made between invaded and non-invaded sites concerning abundance, biomass, richness and diversity of fish communities. In addition, we compared the physiological condition of the sampled species. A total of 2307 fishes belonging to six different species were collected and results indicated almost no negative (except diversity) effects at the community level. However, species-specific analysis revealed a decrease in the abundance of the Iberian chub Squalius carolitertii in invaded sites. We also observed a lower physiological condition of the brown trout Salmo trutta. Although the ecological effects appear to be subtle, ongoing monitoring of signal crayfish populations and their effects on fish communities is essential, using this study as a baseline for future comparisons. Additionally, urgent management measures—such as controlling and containing signal crayfish populations and raising local awareness—should be considered, given the conservation significance of the study area and the potential negative ecological effects of this non-native species.

2025Journal article

Embargoed access