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A highly productive coastal zone plays an important role in various stages of fish life cycles, e.g., spawning migrations, fish reproduction, larval development, juveniles growing, etc. Therefore, coastal biotopes significantly contribute to commercial fish species recruitment. Although the eastern Gulf of Finland is rich in shallow coastal water, its coastal fish communities and the influencing environmental variables are still significantly understudied. We investigated the composition and distribution of coastal fish species and the impact of abiotic and biotic environmental factors in the eastern Gulf of Finland during field surveys in 2011–2017. In total, 34 fish species were recorded at shallows. The coastal fish community demonstrates a low degree of heterogeneity despite a highly heterogeneous environment. Five freshwater species are widely distributed and the most frequent in the area. Three key environmental variables influencing the coastal fish community of the eastern Gulf of Finland were: (i) salinity, (ii) filamentous algae presence, and (iii) macrophytes presence. Fish community structure was also influenced by the sampling season. Discriminating and typifying taxa were performed for each environmental variable. We suggest that obtained results might be useful for future environmental studies in the region and fish community modeling.

The article examines the characteristics of the invasive tubenose goby population that has become established in the eastern Gulf of Finland in the last 15 years. The species inhabits the most part of the studied area, and mainly occurs in waters with salinity equal to or lower than 3 ‰. Abundance of the tubenose goby is positively correlated with the density of filamentous algae, but not with other estimated parameters (substrates, macrophytes, water characteristics). The tubenose goby in the Gulf of Finland reached 62 mm Sl and age 1+. Age composition changed from mature female predominance to the male predominance during the season. Numerous juveniles and spawning adults were observed. The tubenose goby demonstrates successful naturalization in the new conditions and was numerically dominant in the coastal fish assemblage in summer.

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