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The modern distribution of invasive amphipods of Baikal (Gmelinoides fasciatus (Stebbing, 1899), Micruropus possolskii Sowinsky, 1915) and Ponto-Caspian origin (Pontogammarus robustoides Sars, 1894, Chelicorophium curvispinum (Sars, 1895)) in Lake Ladoga is described. The heterogeneity of the distribution of quantitative indicators of amphipods in different parts of the lake was established. The most widespread species in the littoral zone was G. fasciatus. A decrease in the contribution of G. fasciatus in the bottom communities of macrozoobenthos was noted. The dominant role of G. fasciatus was observed only in those parts of the lake where other species of invasive amphipods were not established yet. The range of Ponto-Caspian amphipods is limited by the boundaries of the Volkhov Bay. A significant increase in the quantitative development of P. robustoides and active southward spread of M. possolskii along the west coast of the lake indicate the ongoing restructuring of littoral biocenoses.

The modern distribution of invasive amphipods of Baikal ( Gmelinoides fasciatus (Stebbing, 1899) , Micruropus possolskii Sowinsky, 1915) and Ponto-Caspian origin ( Pontogammarus robustoides Sars, 1894 , Chelicorophium curvispinum (Sars, 1895)) in Lake Ladoga was shown. The heterogeneity of the distribution of quantitative indicators of amphipods in different parts of the lake was established. The most widespread species in the littoral zone was G. fasciatus . A decrease in the contribution of G. fasciatus in the bottom communities of macrozoobenthos was noted. The dominant role of G. fasciatus was observed only in those parts of the lake where other species of invasive amphipods did not penetrated yet. The habitat of Ponto-Caspian amphipods is limited by the boundaries of the Volkhov Bay. A significant increase in the quantitative development of P. robustoides and active dispersal of M. possolskii to the South along the west coast of the lake indicate the ongoing structural restructuring of littoral biocenoses.

Amphipods play the leading role among alien species in Lake Ladoga. In particular, the Baikal species Micruropus possolskii Sowinsky, 1915 is becoming increasingly important here. The purpose of this paper is to present updated data on the appearance of M. possolskii in Lake Ladoga and on the temporal and spatial dynamics of its development and expansion in this water body. The species was initially recorded in the Shchuchiy Bay of Lake Ladoga in 2003. Its spread to the south to the Petrokrepost Bay (where it was recorded in 2017) is shown. The further expansion of the species in Lake Ladoga and its significant quantitative development in the colonized biotopes and possible expansion to Lake Onega and the Neva Bay of the Gulf of Finland are expected.

The issue of the formation of the compound composition of low-molecular-weight organic compounds in aquatic macrophytes, which make up their low-molecular-weight metabolism, has hardly been studied when introducing them into new habitats. The study aims to compare the component composition of the low-molecular-weight metabolome of sago pondweed (Potamogeton pectinatus L.) on the low-molecular-weight organic compounds contained in the essential oil from the invasive population in the Lake Ladoga and the populations from the native range in Astrakhan Region, Russia. Gas chromatography–mass spectrometry was the major research method. Upon the invasion of P. pectinatus into Lake Ladoga, there was a change in the content of various groups of low-molecular-weight organic compounds in the essential oil and a change in the complex of major components. Fatty acids (29.3–40.0%) and ketones (14.5–18.5%) prevailed in the low-molecular-weight metabolome of sago pondweed in the lakes of the native range. Ketones (27.4%) and aldehydes (18.1%) were the main groups in this species inhabiting Lake Ladoga. About a third of the compounds in the composition of the low-molecular-weight metabolome were specific both to the invasive population of the sago pondweed in the Lake Ladoga and to the population from the lakes of the native range. The plasticity of the metabolism of P. pectinatus allows it to adapt to a wide spectrum of abiotic conditions and different biological environments and to settle in new habitats, primarily those under anthropogenic impact.

The role of invasive amphipods (Baikalian species Gmelinoides fasciatus (Stebbing, 1899) and Ponto-Caspian Pontogammarus robustoides G.O. Sars, 1894 and Chelicorophium curvispinum (G.O. Sars, 1895)) in transformation of the Lake Ladoga ecosystem is assessed. It is shown that presently G. fasciatus plays the main role. Invasion of G. fasciatus into Lake Ladoga has led to an increase in productivity of the littoral benthic communities and more efficient utilization of the energy coming into the littoral zone. It is confirmed that P. robustoides and C. curvispinum are established in the lake. The zone of their dwelling may extend, and the role in the littoral habitats may increase. The analysis of the ecological state of the lake with new indices of the concept for assessing the risks of aquatic species invasions reveals a high degree of transformation of the Lake Ladoga ecosystem.

The invasive amphipod Chelicorophium curvispinum (G. O. Sars, 1895) (Amphipoda, Crustacea) was first recorded in Lake Ladoga in the area of Volkhov Bay in August 2009. The data on quantitative development of this species and two other alien species of amphipods (Baikal Gmelinoides fasciatus (Stebbing, 1899) and Ponto-Caspian Pontogammarus robustoides G.O. Sars, 1894) in three different biotopes in the littoral zone of the lake are presented. The necessity of further detailed studies of new alien species distribution in Lake Ladoga is emphasized since their introduction can pose a serious threat to the ecosystem in the littoral of largest European lake.