Here to stay: evaluating establishment of eastern tubenose goby Proterorhinus semipellucidus (Kessler, 1877) in the Baltic Sea with otolith microchemistry and structure

In 2020, the presence of a novel non-indigenous species, eastern tubenose goby Proterorhinus semipellucidus (Kessler, 1877), was documented in the Gulf of Finland, Baltic Sea. As tubenose goby invasion may have a comprehensive ecological impact on the local ecosystem, it has to be confirmed whether the species has established an independently reproducing population or persists through continuous invasions in this area. We examined the otolith microstructure to determine the age of specimens sampled from the southern and northern coasts of the Gulf of Finland. Additionally, otolith microchemistry analysis was carried out on the southern coast specimens. Otolith microstructure revealed the population’s age structure, showing the presence of different age classes, including younger individuals. The microchemistry analyses suggested that the specimens had hatched in brackish water salinities similar to those found in the sampling areas. This indicates local reproduction instead of introduction from the virtually freshwater Neva Bay, which is most likely the donor area of the studied populations. These data confirm the establishment of a self-sustaining reproducing population of eastern tubenose goby in the Gulf of Finland, eastern part of the brackish Baltic Sea.