Jasna Lajtner

Conservation status of freshwater mussels in Europe: state of the art and future challenges.

Freshwater mussels of the Order Unionida provide important ecosystem functions and services, yet many of their populations are in decline. We comprehensively review the status of the 16 currently recognized species in Europe, collating for the first time their life‐history traits, distribution, conservation status, habitat preferences, and main threats in order to suggest future management actions. In northern, central, and eastern Europe, a relatively homogeneous species composition is found in most basins. In southern Europe, despite the lower species richness, spatially restricted species make these basins a high conservation priority. Information on freshwater mussels in Europe is unevenly distributed with considerable differences in data quality and quantity among countries and species. To make conservation more effective in the future, we suggest greater international cooperation using standardized protocols and methods to monitor and manage European freshwater mussel diversity. Such an approach will not only help conserve this vulnerable group but also, through the protection of these important organisms, will offer wider benefits to freshwater ecosystems.

Differences in tolerance to anthropogenic stress between invasive and native bivalves.

Tolerance towards environmental stress has been frequently considered as one of the key determinants of invasion success. However, empirical evidence supporting the assumption that invasive species can better endure unfavorable conditions compared with native species is limited and has yielded opposing results. In this study, we examined the tolerance to different stress conditions (thermal stress and trace metal zinc pollution stress) in two phylogenetically related and functionally similar freshwater bivalve species, the native Anodonta anatina and the invasive Sinanodonta woodiana. We assessed potential differences in response to stress conditions using several cellular response assays: efficiency of the multixenobiotic resistance mechanism, respiration estimate (INT reduction capacity), and enzymatic biomarkers. Our results demonstrated that the invasive species overall coped much better with unfavorable conditions. The higher tolerance of S. woodiana was evident from (i) significantly decreased Rhodamine B accumulation indicating more efficient multixenobiotic resistance mechanism; (ii) significantly higher INT reduction capacity and (iii) less pronounced alterations in the activity of stress-related enzymes (glutathione-S-transferase, catalase) and of a neurotoxicity biomarker (cholinesterase) in the majority of treatment conditions in both stress trials. Higher tolerance to thermal extremes may provide physiological benefit for further invasion success of S. woodiana in European freshwaters, especially in the context of climate change.

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha in the Drava River

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha were examined in mussel populations from the Drava River. The reproductive cycle was studied by histological examination of the gonads and quantified by an image analysing system to determine changes in volume of the entire visceral mass, gonads, digestive glands and in particular the volume of trematodes. Results confirmed that (1) gonads of D. polymorpha were affected by B. polymorphus infection more than any other organ and (2) development of cercariae in sporocysts of B. polymorphus coincides with host gonad maturation. This is the first study in which the image analysing system was used to determine the effect of trematodes on the reproductive cycle of D. polymorpha. Also, this is the first record of sporocysts of B. polymorphus in D. polymorpha in this part of Europe.

Aquatic Macroinvertebrates of the Sava River

The objective of this chapter is to present the data on aquatic macroinvertebrate communities along the Sava River, based on investigation performed during 2011 and 2012 at 12 sampling sites within the sector between Vrhovo (Slovenia) and Belgrade (confluence to the Danube). During our study 227 macroinvertebrate taxa were recorded in the Sava River. Having in mind that upper stretch of the Sava River was not covered by this work (alpine and subalpine stretch), as well as based on the review of previous works on the macroinvertebrate fauna of the Sava River, more than 300 species will be confirmed for the Sava River. The data on the distribution of aquatic macroinvertebrates revealed five different stretches—alpine, subalpine, Upper Sava plain, Middle Sava and Lower Sava. Physical habitat degradation, pollution and pressure caused by biological invasions were found to be the main factors of endangerment of aquatic macroinvertebrate fauna diversity. There is an obvious need for further investigation of the Sava River in order to complete the data on aquatic macroinvertebrates and to provide the basis for accurate assessment of environmental status of the river.

ZOOPLANKTON STRUCTURE IN TWO INTERCONNECTED PONDS: SIMILARITIES AND DIFFERENCES

Abstract The research of zooplankton diversity, abundance and trophic structure was conducted during the summer period in pelagial zone on the longitudinal profile of the Sutla River Backwater. Investigated site consists of two interconnected basins: transparent Upper Basin with submerged macrophytes and turbid Lower Basin without macrophytes in the littoral zone. In the Upper Basin, abundance and diversity of zooplankton in the pelagial was higher in comparison to the Lower Basin, with prevailing species of genus Keratella as microfilter-feeder, and genera of Polyartha and Trihocerca as macrofilter-feeder rotifers. On the contrary, in the Lower Basin, crustaceans dominated in abundance. Microfilter-feeder cladoceran (Bosmina longirostris) and larval and adult stages of macrofilter-feeder copepod (Macrocyclops albidus) prevailed in the Lower Basin. Fish predation pressure was more pronounced in the pelagial of the Upper Basin, indicated by low cladoceran abundance in the surface layer. Although the studied basins were interconnected, results indicate significant (Mann-Whitney U test, p < 0.05) differences in the zooplankton structure as a potential result of the macrophyte impact on environmental conditions and fish predation pressure.

Lifting the curtain on the freshwater mussel diversity of the Italian Peninsula and Croatian Adriatic coast

Freshwater mussels of the order Unionida have been dramatically declining globally. Despite their ecological importance, conservation of these animals has been hindered by unresolved taxonomy and a lack of data on the distribution and status of populations, especially in southern Europe. Although the Italian Peninsula has been noted as a centre of endemism and one of the major refugia of the glacial ages for several taxa, few studies have been performed on the genetic diversity of Unionida. Most importantly, the taxonomic status of several freshwater mussel populations of the Italian Peninsula is still unresolved. Here we present the first comprehensive dataset for the Unionida of the region spanning Italy and the coastal Croatian region (west of the Dinaric Alps). In total, 191 specimens were collected (85 Anodonta, 64 Unio, 17 Microcondylaea bonellii and 25 Sinanodonta woodiana) from 34 sites across the Italian Peninsula and coastal Croatian river basins for molecular identification (COI, 16S and 28S). Genetic analyses were performed to understand major phylogenetic and phylogeographic patterns. Seven species were detected: three Anodonta species (A. anatina, A. cygnea and A. exulcerata), two Unio species (U. mancus and U. elongatulus), Microcondylaea bonellii, and the invasive Sinanodonta woodiana. The presence of three endemic species (A. exulcerata, U. elongatulus and M. bonellii) confirms the importance of the region as a centre of endemism for freshwater mussels. The Apennine Mountains act as an important biogeographic barrier.

Impact of water level fluctuation in shaping of zooplankton assemblage in shallow lake

Abstract Shallow lakes are strongly affected by global climate changes reflected in significant parameters of ecosystem deterioration, i.e. biodiversity decrease, and water turbidity. Zooplankton research in Škrčev kut oxbow lake (Krapina River watershed, NW Croatia, Europe) was conducted during the summer of 2012 and 2013 with the aim to determine the effect of inter-annual, short-timescale changes of hydrological regime on environmental conditions, macrophytes, zooplankton and fish assemblage within an oxbow lake in the temperate region. Within one-year period the water level increased by 2 meters. This caused a significant reduction of floating-leaved macrophytes (i.e. Nuphar lutea), while turbidity, ortho-phosphate and chlorophyll a concentrations increased. These altered ecological conditions were reflected in the shift from floating-leaved macrophytes at the lower water level to phytoplankton-dominated lake at the higher water level. Zooplankton underwent significant alteration in assemblage. The results suggest that fish preference suppressed cladocerans and enhanced the rotifer and copepod abundance. Our results indicate that even in a short-timescale zooplankton assemblage mediates in the modification of ecosystem functioning.

Disentangling food webs interactions in the littoral of temperate shallow lakes

Elucidation of food web interactions provides better understanding of ecosystem functioning, indicates anthropogenic impacts which often cause alterations in environmental conditions and detoriorations in feeding network in terrestrial and aquatic ecosystems. The importance of microfauna and macroinvertebrates in littoral zones of shallow waters has poorly been studied regarding their trophic interactions. This study compares invertebrate assemblage and food web interactions among epiphyton, zooplankton and benthic macroinvertebrates across structural heterogeneity in the littoral zone of three temperate shallow water bodies. Submerged and structurally-complex stands of Ceratophyllum demersum inhabited higher abundance of cladocerans and supported higher diversity and biomass of epiphytic protozoans and invertebrates in comparison to floating-leaved Nuphar lutea stands. Analysis of the ecosystem functioning illustrated the increased biomass of macroinvertebrate predators and a preference of predation over planktonic crustaceans in more complex macrophyte stands. Food webs displayed higher complexity and size with habitat heterogeneity, while epiphyton and zooplankton shared the important fraction in food resources among the invertebrate trophic network. Results of food web modelling indicated zooplankton and epiphyton as more vulnerable to invertebrate predation in the complex submerged macrophytes than in floating-leaved macrophyte stands. Integrated community, ecosystem and food web approaches in explanation of complex trophic interactions in the littoral zones justified an increase in diversity and food-web functional complexity with structural heterogeneity of microhabitats.

Seasonal distribution of the zebra mussel larvae in the dam reservoirs Dubrava, Čakovec, and Varaždin, Croatia

Rad se bavi problematikom vertikalne i horizontalne stratifikacije licinki skoljkasa Dreissena polymorpha u akumulacijskim jezerima hidroelektrana Dubrava, Cakovec i Varaždin. Prikazana je distribucija i gustoca licinki D. polymorpha ovisno o koncentraciji klorofila i temperaturi vode.

Zooplankton in the dam reservoirs Hazna and Vidara, Bosnia and Herzegovina

Dam reservoirs Hazna and Vidara were constructed in 1967 with the purpose of preventing flooding of the lowlands in the Gradasnica river basin, and the communities and industrial zone around the town of Gradacac. They were the result of conversion of the streams Hazna and Vidara. The average lenght of the reservoir Hazna is about 1000 m, and its width is approximately 200 m. Total volume is about 630 000 m3. The maximum depth of the reservoir is 17 m, while the average depth is 3 m. The size of the Hazna basin area is about 10 km2. The dam reservoir Vidara is 2 km far from Hazna. The average lengh is 1500 m, its width is 350 m. The reservoir volume is 3 440 000 m3. The maximum depth of the reservoir is 17 m, while the average depth 6.7 m. The basin area is over 20 km2. Water quality was investigated to determine whether the water of the reservoirs could be used for drinking. The biological and bacteriological quality of the water and its physico-chemical characteristics were studied. This paper mainly deals with zooplankton community which is an important group for the trophic degree estimation.