A team of researchers has published the first nationwide assessment of established non-native species in Türkiye in the journal NeoBiota. The study identifies 271 species that may pose significant threats to the country’s biodiversity, ecosystem functioning, and socio-economic systems, providing a crucial baseline for future conservation and biosecurity efforts.

Using a recent global database of non-native established species, the researchers initially identified 1,092 non-native species within Turkish borders. Through a rigorous review by taxonomic experts, the team filtered out native, cryptogenic, and non-established species, narrowing the focus to 271 confirmed established species.

Of these, marine species are by far the most prevalent, with 198 classified as strictly marine, followed by 42 terrestrial and 27 freshwater species. This trend reflects Türkiye’s extensive coastlines along the Black, Aegean, and Mediterranean seas, which offer vast ecological niches. Furthermore, the coastal regions, characterised by dense populations, robust economies, and intensive trade networks, create multiple human-mediated pathways that can facilitate the introduction and establishment of non-native species.

The assessment also revealed a clear west-to-east gradient, with non-native species concentrated in the western part of the country and decreasing toward the east. The highest concentrations were found in Kayseri and Muğla, each hosting 37 established species, followed closely by Antalya with 34.

In terms of biogeographic distribution, nearly half of the established species originated from the Indo-Malayan realm, followed by the Australasian realm.

A significant concern raised by the researchers is the substantial impact gap in national reporting. Specifically, the majority of established non-native species in Türkiye had no reported impacts (n = 224; 83%), although this number decreased to 157 (59%) at the global scale. While only 17% of established species currently have documented impacts within Türkiye, 41% of these same species are known to cause impact elsewhere.

These findings suggest that many species in Türkiye have not yet undergone formal impact assessments. Among those with known effects, ecological and environmental damages were the most frequently cited, primarily driven by biological mechanisms such as competition, predation, and rapid growth.

The outlook for species already established in Türkiye is particularly concerning. Currently, 50% of the 62 species screened using the Aquatic Species Invasiveness Screening Kit pose a high to very high risk of invasiveness. These proportions are projected to exceed 60% under future climate warming scenarios.

Coordinated national efforts will be essential to mitigate the long-term impacts on Türkiye’s biodiversity and ecosystems.

- the researchers conclude

The study therefore underscores the urgent need for systematic monitoring, improved impact assessments, and climate-informed risk management strategies.