Zita R. Gasiūnaitė

Inventory of the taxonomical composition of the plankton ciliates in the Curonian Lagoon (SE Baltic Sea)

Species composition of plankton ciliates was studied in the Curonian Lagoon in 2007–2008 and compared to long term investigations dating back to the 1980th. In total, 152 taxa were identified at the level of species or genera. More species (76 species/higher taxa) was found in the estuarine part of the Lagoon due to temporally unstable salinity and the presence of both freshwater and brackish/marine species. Some of the brackish/marine species: Tintinnopsis baltica, Tintinnopsis kofoidi, Cothurnia maritima, Lohmaniella oviformis, Lohmaniella spiralis and Helicostomella subulatum were recorded for the first time in the lagoon. The ciliate community at the freshwater sites was less diverse, containing 63 species/higher taxa in the central stagnant part of the Lagoon and 47 — in the Nemunas River avandelta. The comparison of present and past studies revealed that the use of a single live-counting method could lead to underestimation of small nanociliate species, whereas examination of Lugol fixed material provides relatively poor taxonomic information.

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...

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.