Jūratė Lesutienė

Alien Malacostracan Crustaceans in the Eastern Baltic Sea: Pathways and Consequences

The recent invasion history of malacostracan crustaceans into the eastern Baltic Sea is reviewed with 16 alien species being recorded from the easternmost area. These invasives constitute 3% of the total species richness (50% of the alien biota), and comprise up to 80% of the total benthic biomass in several localities. The Ponto-Azov-Caspian species are the most diverse and abundant component. Their taxonomical and ecological dominance could be explained by a combination of factors including similarities between the Baltic, the donor regions and the waterway network that allows their dispersal. The high vulnerability of the Baltic Sea to invasion may be a consequence of low native biodiversity coupled with anthropogenic and natural factors. The potential impact of alien Malacostraca on the native community was assessed following predatory studies of alien amphipods on native benthic biota. These studies indicated that the alien amphipods may alter the structure of their prey communities. Alien crustaceans have outnumbered or even completely replaced native species and/or earlier established invaders locally in the eastern Baltic Sea.

Habitat-Induced Heterogeneity in the Curonan Lagoon Littoral Assemblages: Mysids, Juvenile Fish and Plankton Crustaceans

Zooplankton, juvenile fish and mysid assemblages were investigated in adjacent vegetated and un-vegetated littoral habitats of the Curonian Lagoon (SE Baltic Sea). Juvenile perch (Perca fluviatilis) showed significant habitat partitioning while roach (Rutilus rutilus) did not. The proportion of perch was higher in vegetated habitats, and its foraging on Daphnia was lower in open areas. Roach preferred frequent shifting between habitats, and foraged more intensely on Daphnia and copepods in un-vegetated areas or fed on small-sized chydorids regardless of habitat facilitation. Two omnivorous Ponto-Caspian mysids (Limnomysis benedeni and Paramysis lacustris) tend to aggregate in vegetation during nocturnal migrations. However, their hypothetically increased predatory potential did not show a clear structuring effect on zooplankton distribution in littoral habitats at night. In contrast, the research cases showed that zooplankton distribution heterogeneity is more pronounced during the day. We suggested sever...

Feeding activity and diet composition of round goby (Neogobius melanostomus, Pallas 1814) in the coastal waters of SE Baltic Sea

Abstract Feeding activity and diet composition of round goby were investigated in the south-eastern Baltic Sea, the Lithuanian coastal waters during May-October 2012 in order to determine main feeding objects and seasonal periods when native fauna could be most affected by predation of this highly invasive species. In total, prey represented by 18 taxa was found in the gut contents of dissected fish. Feeding activity of round goby varied depending on the body size, sex and stage of the reproduction period. The gut contents of < 50 mm specimens were dominated by zooplanktonic and meiobenthic organisms, whereas larger individuals (50–99 mm) shifted to amphipods and mollusks. Individuals of the intermediate 100-200 mm length had a variable diet, changing depending on the season; in spring they mostly preyed on Macoma balthica, in summer − on polychaetes, while in autumn the contribution of Mytilus trossulus and fish considerably increased in their diet. Diet composition of individuals ≥ 200 mm was relatively constant in the course of the study with substantial preference to M. balthica. These findings imply that benthic fauna, particularly a newly settled generation of epibenthic mollusks in autumn is under strong predatory pressure of the round goby.

Abundance dynamics and functional role of predaceous Leptodora kindtii in the Curonian Lagoon

The abundance and distribution of predatory cladoceran Leptodora kindtii was investigated in the estuarine lagoon (Curonian Lagoon, SE Baltic Sea). Three hydrodynamically different parts of the lagoon were selected, representing transitory oligohaline, intermediate freshwater and stagnant freshwater sites. L. kindtii was least abundant at the oligohaline site, never occurring at salinities greater than 4 psu. At the two freshwater sites, the abundance of L. kindtii varied from a low of <0.1 up to 2.2 indv. L−1 during peak abundance. Two peaks of L. kindtii abundance were observed with timing differences between stations: at the stagnant site the population of L. kindtii peaked two weeks earlier relative to the more hydrodynamically active sites, likely due to a 2°C higher May temperature. The small body size of L. kindtii in the lagoon (seasonal mean 2.68±0.6 mm) shows high fish predation pressure and predicts small cladocerans, juvenile copepods and rotifers being in the preferred prey size range. The calculated L. kindtii daily consumption during the population peak was as high as 100% of the daily zooplankton production, which implies high potential of this predator to shape the grazing zooplankton community in the lagoon.

Triple stable isotope analysis to estimate the diet of the Velvet Scoter (Melanitta fusca) in the Baltic Sea

This study quantifies contributions of different food sources in the winter diet of the Velvet Scoter (Melanitta fusca) in coastal waters of the Lithuanian Baltic Sea using non-lethal avian sampling. We highlight the application of stable sulphur isotope ratios as complementary to stable carbon and nitrogen isotope analysis in order to discriminate sandy bottom macrozoobenthos organisms as potential food sources for the Velvet Scoter. Selection of the most relevant trophic enrichment factors and Monte Carlo simulations in order to choose the best fitted model were undertaken. The stable isotope mixing model revealed the main contributions of a group of bivalves, Mya arenaria and Cerastoderma glaucum, to be 46–54%, and while the crustacean, Saduria entomon, comprised 26–35% of the diet.