Biological invasions are of increasing global concern. They impact on biodiversity and may result in high economic loss. This demands improvement in knowledge of the dynamics of species dispersal with the goal of preventing future invasions, and predicting and reducing undesirable impacts. This study reports on non-indigenous macroinvertebrate species (NIMS) which have invaded Lithuanian fresh waters. Fifteen NIMS have been recorded during a 12-year study. They include one cnidarian, two molluscan and twelve crustacean species. The deliberate introduction of peracaridans and crayfish for fishery and aquaculture enhancement has substantially contributed to the current NIMS composition. Invaders of Ponto-Caspian origin are dominant, and the collector-gatherers are the largest group with respect to feeding mode. Current NIMS distributions, the history of their primary invasion and patterns of local dispersal are analysed. The main invasion vectors have been inland shipping and deliberate introductions, while secondary spread proceeded both naturally and by various human mediated vectors. The current distribution of most NIMS may remain constant in the future, whilst further expansion of a few NIMS, which possess good dispersal abilities and are well-adapted to freshwater environments, seems very probable. Using multivariate analysis of data from water bodies with established peracaridan invaders, allowed predictions on which unsurveyed water bodies could contain such invaders. Invasions of new NIMS and diversification of donor areas, pathways and vectors are considered. RÉSUMÉ Les espèces de macroinvertébrés non-indigènes dans les eaux douces lituaniennes, Partie 1 : distribution, dispersion et devenirLes invasions biologiques constituent une préoccupation mondiale croissante. Elles ont une incidence sur la biodiversité et peuvent entraîner des pertes écono-miques élevées. Cela exige l'amélioration des connaissances sur la dynamique de la dispersion des espèces dans le but de prévenir les invasions futures, et de prédire et réduire les effets indésirables. Cette étude liste les espèces de macroinvertébrés non-indigènes (NIMS) qui ont envahi les eaux douces lituaniennes. Quinze NIMS ont été enregistrées au cours d'une étude de 12 ans. Elles comprennent un cnidaire,

The chief aim of the present study was to reveal changes in a littoral macroinvertebrate community induced by the invasion of the New Zealand mud snail (Potamopyrgus antipodarum). For that purpose, we compared relevant aspects of the lake littoral macroinvertebrate community in pre- and post-invasion periods and determined the trophic position of P. antipodarum in the lake food web by performing the stable isotope-ratio analysis. The analyses performed showed that P. antipodarum is a primary consumer that may utilise a wide range of primary food sources. Overall, our study showed the following effects of the P. antipodarum invasion on the macroinvertebrate community: a definite increase in the total macroinvertebrate biomass, a significant increase in the local macroinvertebrate family richness and diversity, a shift in the community composition from crustacean- to gastropod-dominated. However, P. antipodarum invasion was not found to affect the biomass of local macroinvertebrates, which remained unchanged.

Summary In this overview, we consider the rationale and practice of invertebrate introductions into Lithuanian waters, the current distribution of introduced species, test the theoretical expectations of introduction of peracaridan species into lakes, and summarize the large‐scale consequences of these translocations. After some early attempts to transfer locally available species within the country, peracaridan species from the Ponto‐Caspian region were introduced into Lithuanian waters during the 1960s (Pontogammarus robustoides, Obesogammarus crassus, Chaetogammarus warpachowskyi, Paramysis lacustris, Limnomysis benedeni and Hemimysis anomala). After their establishment at the site of first introduction in a newly constructed water reservoir on the Nemunas River, further deliberate introductions into Lithuanian lakes and water reservoirs, as well as into more distant areas, were undertaken. These introduced species soon contributed to fish diet and a subsequent increase in the production of commercially important fish was envisaged. However, our collation of available data does not support the enhancement of fish production in Lithuanian lakes. Although perch (selected as a model fish species) assimilated the introduced species into diet and sometimes in large quantities, there was no subsequent influence on somatic growth rates when compared with perch from lakes devoid of alien peracaridans. Comparisons of littoral fish communities of different lakes, and commercial catches in the lake with the most numerous populations of introduced species also indicate no significant effect on fish production. Negative consequences of introduction are more than obvious in contrast. To date, most of the introduced Ponto‐Caspian amphipod and mysid species occur in different sites of the Baltic Sea basin outside Lithuania, and their further dispersal may be expected. These species, especially amphipods, have proved to be highly ecologically aggressive, inducing change in resident macroinvertebrate communities and causing increase of biological contamination (i.e. detract from naturalness). Thus, the introduction of alien fodder species was ill advised from an economic, and even adverse from an environmental perspective.

Background. The round goby, Neogobius melanostomus (Pallas, 1814), is a recent invader in the Curonian Lagoon, SE Baltic Sea. As invasive species are among the most severe threats for biodiversity loss and can induce food web alterations, the development of round goby population in the Curonian Lagoon and its possible impacts on fish community and the entire ecosystem are of great scientific interest. This research reports on the expansion and trophic role of round goby in the Curonian Lagoon. Materials and methods. Occurrence and abundance of round goby was investigated using a beach seine and gill nets at the northern and central parts of the Curonian Lagoon during a six-year period from 2007 to 2012. The trophic niche of the newcomer was revealed by applying gut content and stable isotope analyses (SIA). A total of 61 samples of other fish species were taken for SIA in order to reveal with which resident fish species the exploitative competition could be expected. Stable isotope mixing models were used to evaluate the contribution of round goby to the nutrition of top predators of the Curonian Lagoon: European perch, Perca fluviatilis Linnaeus, 1758; pike-perch, Sander lucioperca (Linnaeus, 1758); great cormorant, Phalacrocorax carbo; and grey heron, Ardea cinerea. Results. The survey showed that round goby expanded its distribution area and recently occurs in the entire Lithuanian part of the Curonian Lagoon. Variation in the density of round goby suggests that the invader's abundance may be stabilised in the northern part of the lagoon. Gut content and stable isotope analyses showed round goby being mainly benthivorous. The largest trophic overlap with respect to SIA was detected between the invader and ruffe, Gymnocephalus cernua (Linnaeus, 1758), the fish which presumably exploits the same habitat type. According to stable isotope mixing models round goby was included with considerable shares into the diet of top predators. Conclusion. The further expansion of round goby inside the Curonian Lagoon is ongoing. However, there is evidence on population density stabilisation in the northern part of the lagoon. Native benthivorous fish, especially ruffe, may be affected through competition for food resources in habitats where the newcomer is numerous. Round goby significantly contributes to the diet of piscivorous fish and birds. That may promote the regulation of invader population abundance in the lagoon.

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