Marbled crayfish, a new invasive species for Crimea and Russia, have been discovered in Crimean rivers

Fig.1: A specimen of the marbled crayfish *Procambarus fallax* (Hagen, 1870) from the Alma River (Crimea) and its coloration during life

Research conducted by the scientists from the A.N. Severtsov Institute of Ecology and Evolution of the Russian Academy of Sciences (Moscow) and the A.O. Kovalevsky Institute of Southern Sea Biology of the Russian Academy of Sciences (Sevastopol) in 2022–2024 revealed the presence of the invasive marbled crayfish Procambarus fallax (Hagen, 1870) (Decapoda: Cambaridae) in western Crimea, in the lower reaches of the Alma and Belbek rivers. The presence of this species was also reported at the mouth of the Chernaya River.

"This is the first reliable evidence, based on a comprehensive morphological and molecular genetic analysis, of the presence of this highly invasive species on the Crimean Peninsula and yet another discovery of an invasive species in the fauna of Russia. Phylogenetic analysis showed that the Crimean specimens share the same haplotype as the invasive subpopulation currently recorded in the waters of Europe (Sweden), Japan, and Madagascar," notes Ivan Marin, PhD in Biology and Senior Researcher at IEE RAS.

The studied individuals of the European subpopulation, also designated Procambarus virginalis Lyko, 2017, possess a single haplotype, indicating a relatively recent introduction of the species. Research by American scientists has shown that both parental haplotypes of P. virginalis were inherited from the original subpopulation of P. fallax, a sexually reproducing species native to the Everglades (southern Florida, USA), where triploid individuals of this species have also been identified. The European (invasive) subpopulation is represented exclusively by triploid parthenogenetic individuals (females)—the only known example among decapod crustaceans that reproduce via apomictic parthenogenesis. This characteristic provides the population with exceptional dispersal capacity—colonizing new bodies of water is possible even with the introduction of a single juvenile individual.

The invasive subpopulation also exhibits high ecological plasticity, including tolerance to low oxygen levels and short-term temperature drops below 8°C. In Crimea, in December 2022, this species was discovered in bodies of water that periodically freeze over during the winter. However, at the time of sampling on December 12, 2022, the overnight air temperature dropped to 0°C, and the water temperature in the Belbek River (Sevastopol) was approximately 6–8°C.

The authors of the study hypothesize that the spread of the marbled crayfish in the lower reaches of the Alma and Belbek Rivers may be related to the activity of migratory birds (e.g., mute swans and ducks), which are capable of transporting juvenile crayfish or their eggs on their feet, plants, or feathers. This hypothesis is supported by the disjunctive (discontinuous) nature of the finds' range, which does not correspond to a gradual spread along the riverbeds. Notably, the marbled crayfish coexists at the mouth of the Belbek River with the epigean amphipod Niphargus potamophilus Birštein, 1954 (Amphipoda: Niphargidae), for which this locality remains the only known occurrence in Crimea. It has previously been suggested that this species is most likely carried from one body of water to another by migratory birds.

New data show that marbled crayfish can survive at average annual temperatures of approximately 12°C (typical for Sevastopol). This suggests the possibility of this species appearing, or being discovered soon, in other regions with similar climatic conditions—Anapa (12.4°C), Tuapse (12.4°C), Krasnodar (12.7°C), Sochi (14.4°C), as well as in cooler areas, such as Rostov-on-Don (11°C).

In conclusion, the data obtained convincingly demonstrate the ongoing eastern expansion of this tropical invasive species. However, there is currently no evidence of its significant negative impact on local ecosystems. Unlike many other invasive organisms, the marbled crayfish does not form dense aggregations due to its relatively small size (50–60 mm in adults) and serves as a prey item for a number of predators, including large fish and larger native crayfish species. Significant predation pressure likely limits population sizes and reduces potential impacts on ecosystems of the Crimean Peninsula, where crayfish are currently found only occasionally. However, this species can transmit certain diseases, particularly crayfish plague, a mycotic (fungal) disease that causes widespread mortality in European crayfish.

The work was published in the journal Arthropoda Selecta: Marin I.N., Statkevich S.V. 2025. The first discovery of the invasive marbled crayfish Procambarus fallax (Hagen, 1870) in Crimea // Arthropoda Selecta. Vol. 34. No. 3: 359–364.

This study is the first to mention the presence of invasive crayfish in the Chernaya River.

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