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Upstream migration of the invasive blue crab in the Po River, Italy, highlights the vulnerability of freshwater ecosystems

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Abstract

The Atlantic blue crab (Callinectes sapidus) is one of the most rapidly expanding invaders in the Mediterranean Sea, where it has established populations across all coastal and estuarine habitats. While its impacts in these environments are well documented, little is known about its occurrence and ecological role in inland waters. This study provides the first evidence of significant upstream migration of blue crabs along the Po River and nearby branches (Northern Italy), beyond typical coastal habitat distributions. Blue crab occurrences were based on 50 validated geo-referenced records collected between 2022 and 2025 through fishermen reports. Environmental variables and blue crab upstream distance were analyzed to explore possible drivers of this migration. The potential trophic interactions between blue crab and riverine fish species were also examined through a systematic literature review. The findings revealed that upstream dispersal reached distances of more than 160 km from the sea, primarily driven by adult males. No clear correlation was found between upstream distance reached by blue crab and water temperature, conductivity, dissolved oxygen, or river discharge, suggesting that ecological dynamics, rather than abiotic filtering, likely drive inland expansion. The literature review highlighted only a few documented trophic interactions in European freshwaters, although potential predation by invasive fish species and competition with native fauna may occur. These results underscore the urgent need for targeted monitoring and research to evaluate the ecological consequences of blue crab invasion in freshwater systems, particularly regarding its potential impacts on biodiversity, food web dynamics, and ecosystem functioning.

Data availability

The datasets generated during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We would like to thank the Emilia-Romagna Region – Direzione Generale Agricoltura, Caccia e Pesca for the support and the long lasting collaboration and all fishermen involved in the study, particularly Mr. Luca Bellini.

Funding

This research was conducted as part of the project “Study for the assessment of the ecological status of transitional surface water bodies in the Po River hydrographic basin based on the fish fauna biological quality element and through the application of the Habitat Fish Biological Index, with the aim of achieving an overall assessment of the ecological status of these environmental systems” and as part of fish monitoring program of Emilia-Romagna region.

Author information

Authors and Affiliations

  1. Department of Environmental and Prevention Sciences, University of Ferrara, Ferrara, Italy

    Anna Gavioli, Mattias Gaglio, Davide Cardi, Mattia Corsato, Matteo Melandri, Giuseppe Castaldelli & Mattia Lanzoni

  2. Directorate General for Agriculture, Hunting and Fisheries, Emilia-Romagna Region, Bologna, Italy

    Rubina Sirri

  3. Po River Basin District Authority, 43121, Parma, Italy

    Fernanda Moroni

Authors

  1. Anna Gavioli
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  2. Mattias Gaglio
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  3. Davide Cardi
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  4. Mattia Corsato
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  5. Matteo Melandri
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  6. Rubina Sirri
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  7. Fernanda Moroni
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  8. Giuseppe Castaldelli
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  9. Mattia Lanzoni
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Contributions

GC and ML conceived the study. Data collection and surveys were done by DC, MC, MM, RS and FM. Literature collection, preparation of data and analysis were done by MG and AG. Drafting was done by AG and MG, with revisions from GC. All authors have read and revised the submitted manuscript.

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Correspondence to
Mattias Gaglio or Giuseppe Castaldelli.

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Gavioli, A., Gaglio, M., Cardi, D. et al. Upstream migration of the invasive blue crab in the Po River, Italy, highlights the vulnerability of freshwater ecosystems.
Sci Rep (2026). https://doi.org/10.1038/s41598-026-37990-1

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  • DOI: https://doi.org/10.1038/s41598-026-37990-1

Keywords

  • Biological invasion
  • Atlantic blue crab
  • Freshwater
  • Non-native species
  • Mediterranean basin
  • Callinectes sapidus

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