Investigations of aquatic mollusc assemblages were conducted within a semi-natural catchment of a medium-sized lowland river Liwiec in five habitat types: the main Liwiec River channel, its secondary channels and six tributaries, as well as in natural ponds and man-made ditches within the river floodplains.To assess the contribution of each habitat type to the diversity, I used the species richness, diversity, rarity (species rarity index, SRI) and abundance, as well as the composition and structure of mollusc assemblages and compared them among the habitat types.The spatial pattern of mollusc diversity was analysed based on hierarchical partitioning.Over five years, 54 mollusc species were found, including three listed on the IUCN Red List or in Annexes II and IV of the EU Habitats Directive (Unio crassus Philipsson, Sphaerium rivicola (Lamarck) and Anisus vorticulus (Troschel)).The mollusc metrics in most cases did not differ significantly among the habitat types.All the habitats contributed relatively evenly to the mollusc diversity.The diversity at the site level was generated mainly by alpha component, whereas at the landscape scale habitat heterogeneity (beta component, i.e. β2) was very important.In order to maintain mollusc diversity, conservation efforts ought to focus specifically on the most heterogeneous fragments of the Liwiec River catchment.

The mollusc fauna of a medium-sized lowland river Krzna, which is almost entirely regulated and affected by urbanisation, was surveyed. The aim of the study was to determine if negative effects of urbanisation were evident in mollusc communities: their species richness, diversity and abundance, as well as composition and dominance patterns. Thirty one living mollusc species and empty shells of another two species were recorded. The simplification of the dominance pattern observed especially within and below Łuków and within Międzyrzec Podlaski may point to a negative effect of urbanisation. A decrease in species richness and diversity in response to urbanisation was recorded within Międzyrzec Podlaski, as well as below Łuków and Biała Podlaska. The mean abundance showed an increase in two urban and two downstream stretches. The relatively ambiguous response of malacocoenoses to urbanisation may result from the elimination of sensitive mollusc species by stressors associated with regulation of the river and release of untreated or insufficiently treated sewage in the past decades. Both the regulation of the river and urbanisation may have contributed to the negative effects on the malacocoenoses, but separation of the influence of these two anthropogenic stressors may be very difficult. kEy words: mollusc assemblages, diversity, urban river

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The Liwiec River, the biggest left-bank tributary of the Bug River, drains South Podlasie and Middle Mazovian Lowlands. This study aimed at tracing longitudinal changes in the composition, diversity, dominance pattern and abundance of its mollusc assemblages. Special attention was paid to the role of spatial disturbances in the river continuum, of both natural (tributaries) and anthropogenic origin (sewage treatment plants, small dam). Forty two mollusc species were recorded, with the respective values within the upper (UR), middle (MR) and lower (LR) river sections of 27, 19 and 34. The composition of mollusc assemblages showed some longitudinal changes, but without any clear progression along the river course. However, some differences among the malacofaunas of UR, MR and LR were observed, including large variation in species richness along the river. A relatively small species richness (less than 5 species) was found at 26% of the sites. The rather high total species diversity (γ) resulted mostly from considerable differences in the species composition among the sites. The effect of spatial discontinuities in the river course on the mollusc assemblages was rather weak, but they were more visible than the differences between consecutive sites within free-flowing river sections. kEy words: mollusc assemblages, diversity, longitudinal changes, river discontinuities

Natural river-floodplain systems are heterogenous mosaics of lotic and lentic habitats subjected to dynamic temporal changes connected with hydrological regime, which promote high biological diversity Mollusc assemblages of three habitat types within 10 km section of the lower course of the Liwiec River (East Poland) - the main river channel (MC), the secondary channel (SC) and remnants of the former river channel (FC), were compared to find if they were structured by heterogeneity resulting from hydrological connectivity and disturbance intensity related to it. The influence of selected qualitative environmental variables was also analysed. The investigations were carried out at 19 sites during late spring and late summer in the years 2012-2014, molluscs were sampled from approximately 1 m(2) of the bottom with a hand net, and from macrophytes with a frame.Rich aquatic malacofauna (36 species including 22 gastropods and 14 bivalves) was found within the study area including three species of special interest: Anisus vorticulus (Troschel), Unio crassus Phillipsson and Anodonta cygnea (L.). Bivalves Sphaerium corneum (L.) and Pisidium spp dominated within MC, in SC a few common and ubiquitous species (mainly snails) prevailed, pulmonate snails and some small bivalves of the genus Pisidium were the most numerous molluscs within PC. Principal Component Analysis revealed that current velocity, channel width, bottom sediments and macrophyte abundance were important environmental factors structuring mollusc assemblages. Considerable variation in species composition (beta diversity), especially between the main river channel and two other habitat types (beta(2)) was found. The highest values of mean species richness, Shannon true diversity and Shannon index found in the secondary channel were in accordance with intermediate disturbance hypothesis.

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ABSTRACT The distribution and species richness of aquatic molluscs were analysed within a 186‐km‐long section of a large (755‐km‐long) lowland river floodplain using GIS maps. Special attention was paid to threatened species. An attempt was made to identify local ‘hotspots’ of molluscan diversity and to determine the most important areas for conservation based on species richness, number of threatened species and indices of synthetic conservation (Q) and centres of population density (ICD). Over four years of investigation, carried out in 176 water bodies, a rich malacofauna was identified: 58 species including 20 of elevated conservation concern. GIS maps revealed numerous ‘hotspots’ of mollusc species richness and higher incidence of threatened species, as well as areas characterized by raised Q and ICD indices. Water body size and hydrological connectivity positively influenced species richness and Q values. The highest values of these variables were found in large water bodies having limited surficial connectivity with the river channel. Species richness, numbers of threatened species, and Q and ICD values were significantly higher in younger permanent water bodies compared with semi‐permanent or temporary ones representing advanced successional stages. Spatial visualization data collected in the study area indicate that the most valuable sites for the conservation of aquatic molluscs include both sides of the river in the lower part of the middle stretch of the lower Bug River valley. Copyright © 2013 John Wiley & Sons, Ltd.

Riverine floodplains are regarded as one of the most heterogenous and dynamic ecosystems. In natural state they encompass a variety of wetland sites like pools, lakes, channels etc. related and linked with the flood pulses; being the hot spots of high and specific biodiversity they are often under protection. The diversity and abundance of molluscs in the flood-plain water bodies were investigated in order to find the shaping impact of chemical factors of water and sediments. The water bodies were located within 140 km section of the lower Bug River valley (eastern Poland, 190 to 50 km of the river course). The investigations were carried out in the years 2007-2009 in 25 permanently flooded, 25 semi-permanent sites (i.e. habitats partly dried-up because the water volume has decreased significantly during low river discharge) and 24 temporary water bodies holding water for at least few months (up to 8-9 months). The first group of sites consisted of large water bodies (the area above 1000 m(2), depth mostly exceeded 2 m) representing earlier and middle successional stages. The second group contained relatively shallow (1-1.5 m) water bodies of medium or large size (from below 500 to above 1000 m(2)) representing more advanced successional stages. Temporary water bodies were very diverse in size (from about 100 to 1000 m(2)) their depth ranged from below 0.5 m to about 1 m and they mostly represented less advanced successional stages. Molluscs were collected from the bottom (using a hand net) and from macrophytes (using a frame). Concentrations of oxygen, nitrate and ammonia nitrogen, phosphates, calcium, chlorides, as well as BOD5, pH and conductivity were measured in water. Organic matter, nitrogen and phosphorus content in bottom sediments were determined, as well as C/N and NIP ratio. Permanent water bodies supported the richest malacofauna - 52 species (over 91% of all species found within the study area), whereas in semipermanent sites and temporary ones 29 and 36 mollusc species were found. Mean number of species per site amounted to 18.7 +/- 4.0, 7.7 +/- 3.2 and 9.6 +/- 5.1 in permanent, semi-permanent and temporary water bodies respectively. Mean values of Shannon-Weaver index (H') in three site groups mentioned amounted to 3.18 +/- 0.55, 2.18 +/- 0.72 and 2.07 +/- 0.83, respectively. Mean density of molluscs significantly differed among site groups (from 80 indiv. m(-2) in semi-permanent sites to 292 indiv. m(-2) in temporary ones) being the highest in temporary habitats (the range of values from 34 to 1840 indiv. m(-2)). Phosphates, ammonia nitrogen and pH of water significantly influenced the abundance of molluscs, whereas oxygen concentration and BOD5 affected species richness, diversity and abundance of molluscs within the permanent water bodies. In the other site groups chemical parameters of water did not affect significantly the mollusc communities. The influence of organic matter, nitrogen and phosphorus content in bottom sediments on malacocoenoses was not significant. The quality of organic matter contained in bottom sediments expressed as C/N (the range of values from 8 to over 40) showed structuring influence on malacocoenoses. Low food quality (C/N> 17), especially in many semi-permanent habitats, may constrain the development of molluscan communities.

Usefulness of basic chemical and granulometric parameters of bottom sediments in the assessment of successional stage and condition of floodplain water bodies was analyzed, as well as some aspects of nutritional quality of bottom sediments. Organic matter (OM), nitrogen and phosphorus content and granulometric parameters differed between permanent and temporary, as well as between old and young water bodies. In some habitats despite of relatively low C/N ratio and high OM content sediments were not favourable for detritivores. Organic matter content in sediments of floodplain water bodies may be used in the assessment of C-org and N with high probability.

This study analyses the composition, species richness and diversity (H') of aquatic molluscan communities in temporary water bodies within the valley of the lower Bug River in eastern Poland.The investigations were carried out in 2007-2009 within the section of the valley located between 190th and 50th km of the river course in 50 water bodies.Relatively rich and diverse malacofauna was found in the investigated habitats: 32 snail species and 6 bivalve species.Species diversity (H') in individual water bodies ranged from 0.44 to 3.48.About 40% of all mollusc species showed frequencies of £10%.Dominance patterns varied much among the water bodies.Mollusc abundance ranged from 20 to over 1,800 indiv./m 2 .Considerable species richness and diversity were found both within the active floodplain and the former one.This was probably related to the long duration of many of the investigated water bodies, as well as their periodical hydrological connectivity with permanent ones or river channel.From 9 to 12 samples should be enough to compile representative species list of molluscs inhabiting temporary water bodies, but as many as 28-40 samples would be necessary to obtain complete dataset.

This study analyses the composition and species richness of aquatic molluscan communities within a large sector (over 100 km) of the valley of the Bug, a large lowland river in eastern Poland. An attempt was also made to determine the number of samples sufficient to compile a representative mollusc list within the whole study area and in groups of water bodies representing different degree of permanence, as well as to test the completeness of sampling of the malacofauna. Within the study area, 54 mollusc species were found – 36 snails and 18 bivalves. Up to 27 species were recorded from individual sites with a mean of 8+ 5 species per site. Mean number of species was significantly higher in permanent water bodies than in the two other site groups. Dominance patterns in molluscan communities and frequencies of individual species showed distinct differences within three groups of habitats differing in permanence. Species composition was related to permanence, size, depth, hydrological connectivity and successional stage of water bodies, as well as to the type of bottom sediments and macrophyte abundance. The aquatic malacofauna found within the study area was rich, comprising almost 90% of potential composition based on regional species lists. Rarefaction curves for the total malacofauna confirmed the low probability of finding additional species, whereas temporary and permanent water bodies showed incomplete species lists. About 20 samples should be sufficient to collect representative data in the study area and more than 60 samples would be necessary to collect a nearly complete dataset.

The aim of the present study was to describe the diversity and abundance of the mollusc communities in long and diverse series of riparian water bodies (59 in total) and to compare them with previous (two years before) studies based on much shorter series of sites (21 in total). An attempt was made to check whether the previous analysis of mollusc groupings is suitable to the classification of the riparian sites of a large area.The studies were carried out in the years 2004-2006 in left-bank part of the valley between 53 and 152 km of the course of the lowland medium sized natural river (Bug River, Eastern Poland) in 59 water bodies differing as regards size (from about 0.01 to a few ha), location in the valley, hydrological regime and successional stage. The samples were collected from the bottom (with dredge) and from macrophytes.The high species richness and diversity were found within the study area despite that the natural floodplain fragments were quite small (about 10% of the whole investigated fragment of the river valley). 52 mollusc species were noted: 36 snails and 16 bivalves (over 50% more than in the preliminary series). Relatively rich malacofauna existed in larger and younger water bodies, as well as in some temporary ones, but located in the active floodplain.Species diversity of individual habitats was comparable to that reported from the earlier study (jurkiewicz-Karnkowska 2006), i.e. H' values amounted to 2-3 in most cases. However, there were more cases where H' values exceeded 3, as well as H' values were higher at larger scale, i.e. site groups and the total study area (3.5-4.5).The most common species (F >= 50%) within the investigated area were Lymnaea stagnalis, Bithynia tentaculata, Planorbarius corneus, Anisus vortex, Radix balthica and Viviparus contectus. The most frequent species usually constituted significant components of mollusc communities of individual water bodies. The only species with percentages exceeding 10% of total mollusc abundance at the scale of the study area were R corneus and L. stagnalis. The abundance of molluscs was of the order of several to a few hundred individuals per sample (0.5-1 m(2) of bottom).Basing on the occurrence of molluscs in the investigated habitats I-V groups of water bodies were distinguished applying multivariate analysis. They differed in abundance, dominance pattern and diversity of malacocoenoses, as well as frequencies of individual species. Especially high distinctness of malacocoenoses of small temporary water bodies was found.

The present study aimed at describing composition, species richness, dominance patterns and diversity of mollusc communities as well as frequency of individual species within selected water bodies of the valley of large Polish lowland river (lower Bug River). Suitability of molluscs in the ordination of the investigated habitats was evaluated. The studies were carried out in the years 2003-2004 in left-bank part of the valley between 2.5-6.5 and 90-107 kin of the river course in 21 water bodies heterogenous as regards size, location and successional stage. The dredge was used.34 mollusc species were found: 23 snails and 11 bivalves. At individual sites from 2 to 15 species were noted (4 - 18 including molluscs found only as empty shells). Relatively rich malacofauna existed in larger water bodies in comparison with small stagnant and isolated ones located outside the embankment. Malacocoenoses of the investigated habitats exhibited considerable species diversity (H' = 2-3 in most habitats).Lymnaea stagnalis, Bithynia tentaculata, Planorbarius corneus and Viviparus contectus were the most frequent species (F >= 50%). These species as well as moderately frequent ones constituted significant components of mollusc communities of individual water bodies. Frequencies and dominance patterns of molluscs inhabiting younger and older water bodies distinctly differed. The abundance of molluscs was mostly of the order of several to a few dozen individuals per sample (0.5-1 m(2) of bottom).Principal component analysis and classification (PCCA) basing on the occurrence of molluscs expressed as the classes of abundance enabled to distinguish 4 groups of water bodies, among which 2 were more distinct. The comparison of malacofauna of these two groups exhibited significant difference in frequencies.Species (S) and percentage (Psc) similarities among malacocoenoses of the investigated water bodies were generally weak or moderate, which presumably results from isolation among majority of them. More cases of high values of similarity indices were found within the group of small and shallow water bodies in comparison with larger and deeper ones. This may result mainly from higher habitat homogeneity at later stages of hydrarch succession. Generally higher species than percentage similarity was observed indicating the differences in dominance relations among sites with similar composition of malacofauna.

1. Molluscs (Mollusca) in selected small rivers of the Mazovian Lowland Beata Jakubik Annales UMCS, Biologia CrossRef

The studies on long-term and spatial variability in dominance pattern and abundance of malacofauna in selected habitats of the W∏oc∏awek Reservoir (Central Poland) were made in relation to environmen- tal factors. Abundant and relatively rich in species malacocenoses were dominated by Sphaerium corneum. Malacofauna of shallow biotopes was characterized by higher species richness and lower abundance than molluscs inhabiting the old river bed. Eutrophication, turbidity and transformation of bottom sedi- ments are likely to be the most important fac- tors influencing changes in malacocenoses.

Comparisons of P concentration in soft tissues and shells of molluscs being main components of malacocenoses of the Zegrzynski Reservoir as well as analyses of spatial, temporal and size dependent diversity of P concentration in particular mollusc species were performed. Percent content of P in the soft tissues of the investigated species varied significantly when comparing taxonomically distant species, whereas P level in shells was relatively similar. Owing to the interspecies diversity and size dependence of P concentration, the species composition and dominance patterns of malacocenoses as well as size-frequency relations in populations of dominant species are expected to influence the accumulation of P by molluscs in a given habitat.

The work aimed at the analysis of the structure and abundance of mollusc communities and their connection with environmental factors, especially the influence of Dreissena polymorpha. Molluscs were collected at 21 sampling stations within the Sulejow Reservoir in July 1999 and 2000 using Ekman-Birge's grab and bottom dredge. Generally fauna of molluscs was dominated by D. polymorpha, however in the upper part of the reservoir relative abundance of this species was low. The effect of zebra mussel on malacocenoses resulted in significant differences in species richness and densities between the habitats where this mollusc occurred in lower and higher abundance.