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The rise and fall of an alien: why the successful colonizer Littorina saxatilis failed to invade the Mediterranean Sea


Understanding what determines range expansion or extinction is crucial to predict the success of biological invaders. We tackled this long-standing question from an unparalleled perspective using the failed expansions in Littorina saxatilis and investigated its present and past habitat suitability in Europe through Ecological Niche Modelling. This intertidal snail is a typically successful Atlantic colonizer and the earliest confirmed alien species in the Mediterranean Sea, where, however, it failed to thrive despite its high dispersal ability and adaptability. We explored the environmental constraints affecting its biogeography, identified potential glacial refugia in Europe that fuelled its post-glacial colonisations and tested whether the current gaps in its distribution are linked to local ecological features. Our results suggested that L. saxatilis is unlikely to be a glacial relict in the Mediterranean basin. Multiple Atlantic glacial refugia occurred in the Last Glacial Maximum, and abiotic environmental features such as salinity and water temperature have influenced the past and current distributions of this snail and limited its invasion of the Mediterranean Sea. The snail showed a significant overlap in geographic space and ecological niche with Carcinus maenas, the Atlantic predator, but distinct from Pachygrapsus marmoratus, the Mediterranean predator, further pointing to Atlantic-like habitat requirements for this species. Abiotic constrains during introduction rather than dispersal abilities have shaped the past and current range of L. saxatilis and help explaining why some invasions have not been successful. Our findings contribute to clarifying the processes constraining or facilitating shifts in species’ distributions and biological invasions.

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Data availability

Raw data analysed in this study was obtained from the Global Biodiversity Information Facility database (GBIF, further details in Materials and Methods). The final dataset, refined bioclimatic variables, all the AUC and TSS values for each algorithm and run (further details in Materials and Methods) and codes are available in Supplementary Materials 2.

Code availability

Codes are available in Supplementary Materials 2.


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We are grateful to Luca Mizzan for providing information and insights on L. saxatilis in Venice. We thank Evangelina Schwindt, Anja Marie Westram, Neftalí Sillero and an anonymous reviewer for their comments on a previous version of the manuscript and their contribution to the review of this work.


Funding for this project came from the University of Gothenburg Centre for Marine Evolutionary Biology to KJ and RKB and the MIUR PRIN 2017 grant 201794ZXTL to GB.

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FR and LB designed the study. Data was collected and analysed by LB, SS and FR. FR, RKB, KJ, GB, RD and LB contributed to data interpretation. FR and LB drafted the manuscript. All authors revised and agreed to the manuscript.

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Correspondence to Luciano Bosso or Francesca Raffini.

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The authors declare no conflict of interests.

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Bosso, L., Smeraldo, S., Russo, D. et al. The rise and fall of an alien: why the successful colonizer Littorina saxatilis failed to invade the Mediterranean Sea. Biol Invasions 24, 3169–3187 (2022).

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  • Alien species
  • Ecological niche modelling
  • Evolutionary ecology
  • Failed colonization
  • Intertidal model
  • Mediterranean Sea