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Diversity of Mollusca in lowland river-lake system: lentic versus lotic patches

Jakubik B., Koperski P., Lewandowski K.

Polish Journal of Ecology

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2014

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Vol. 62, nr 2

335--348

EN

Longitudinal organisation of macroinvertebrate fauna along river is one of the most important problem commonly used to explain the functioning of flowing water ecosystems. The river system can be treated as a mosaic of landscapes patches and riverine macroinvertebrates’ community structure is a function of longitudinal changes in its key abiotic patterns. The aims of the study was to analyse the taxonomic structure of molluscs in the river-lake system, to compare river and lake malacofauna and to determine the factors responsible for its diversity in lakes and river stretches. The study based on comprehensive analysis of malakofauna sampled at 10 sites in the Krutynia River and in all 19 lakes it flows through were performed in the years 2008–1011. River Krutynia is one of the most important rivers in Masurian Lakeland (north-eastern Poland) with length of 100 km and mean annual discharge of 10.6 m3 h-1. It forms a characteristic river-lake system typical for the lakeland landscape in Central Europe. The density and taxonomic composition of molluscs were found as strongly dissimilar in a local scale – between closely located lakes and between particular parts of flowing waters, divided by the lakes. Multivariate methods were used to demonstrate a clear dissimilarity of lake and river malakofauna and to show that the mean content of phosphorus, nitrogen and organic matter in bottom sediments were correlated with each other in lakes but not in the river. The most important species differentiating river sites into larger groups with respect to the similarity was Theodoxus fluviatilis while Stagnicola corvus and Anisus vortex were such species differentiating lakes. The numbers and percentages of Dreissena polymorpha and Unionidae were negatively correlated with nutrients in river sediments. There was a strong positive relationship between nutrients’ concentrations in sediments and the percentages of Viviparus, Obtained results of multiple regression indicate a strong effect of nutrient and organic matter concentrations in the sediments and the distance from the site to the lake on the domination structure of molluscs.

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Invertebrate reproduction in astatic water bodies : egg number - body weight relationship in Viviparus viviparus (L.) from oxbow lakes

Jakubik B.

Polish Journal of Ecology

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2012

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Vol. 60, nr 2

363-374

EN

Reproduction is the most important factor in population dynamics and invading freshwater habitats by Viviparus viviparus. This is largely associated with ovoviviparity of these snails. Some traits like steered reproduction, the appearance of young snails during the whole year, protection of embryos by female and delayed reproduction were fixed by natural selection as adaptations increasing the chance for progeny survival. In variable habitats like oxbow lakes seasonally joined to the river channel, Viviparidae start reproducing in the early stage of their life hence increasing a chance for population to survive. Studies on fecundity, embryonic development of V. viviparus and the relationships between these parameters and females. body size and weight, were carried out in oxbow lakes periodically connected to the river (the Bug River, Central Poland). The Bug River is one of a few European rivers which preserved their nearly natural character. No larger hydrotechnical works have been made in its valley, therefore, the river flows in a natural, meandering channel and forms numerous oxbow lakes. The surrounding of studied oxbow lakes is flat and of lowland character with mixed land use structure (arable lands, grasslands, settlements). Oxbow lakes are fed by the runoff from flood terrace, hence their waters are more fertile than those of the river. Two lakes were selected: Lake Szumin, area 17 ha, Lake Wywłoka - area 23 ha. Maximum depth of both lakes is ca 3 m. Samples of V. viviparus were collected in the years 2003-2007 with a bottom drag during the successive seasons from five sites in each oxbow lake. The embryos were found in females of the II (8.1-12.0 mm of width and height), III (12.1-20.0 mm width and 12.1-25.0 mm height) and IV (over 25.0 mm height and over 20.0 mm width) size classes. Three developmental stages were distinguished in embryonic growth: the oval transparent egg capsules (called the youngest embryos), egg capsules with visible contour of a shell (called medium embryos) and snails with a shell (the oldest embryos). The youngest growth stages of embryos (in a form of oval transparent egg capsules) dominated in all size classes of females. Medium growth stages (egg capsules with visible outlines of the shell) and the oldest ones (with shell) were represented in smaller proportion. The highest number of the youngest embryos per female were found in females of the II size class. The proportions of the embryo growth stages varied seasonally. The number of embryos per female and the degree of their development increased with the increase of shell (height, width, dry weight) and body (dry weight) parameters. High fecundity of the youngest females of V. viviparus is probably an adaptation to unstable habitat conditions of oxbow lakes.

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Food and feeding of Viviparus viviparus (L.) (Gastropoda) in dam reservoir and river habitats

Jakubik B.

Polish Journal of Ecology

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2009

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Vol. 57, nr 2

321-330

EN

Studies on feeding of V. viviparus were carried out in the years 1995-2005 in dam reservoir (Zegrzyński Reservoir, Central Poland, 60 km long, mean depth ca 3.5 m, maximum depth at the dam up to 9 m, mean retention time from 1 to 15 days) and in the outlets of its tributaries (the Bug, Narew and Rządza rivers), in the Narew River and - in the years 2003-2006 - also in oxbow lakes of the Bug River. Sex ratio and size structure of snails were estimated. Both the content of intestines (detritus, algae, inorganic matter) and the gut fulfilment were analysed. Performed multi-factor analysis showed the effect of habitat, season and snail size (estimated from shell height) on food mass in the gut. Snails from dam reservoir and outlet stretches of three rivers showed the largest food mass in the gut. Intestines of snails from rivers and oxbow lakes were less filled. The largest food volumes were found in spring and summer. Only in viviparids from oxbow lakes the largest food mass in the gut was noted in the autumn. Food mass in the gut was largest in snails of the I (<8 mm) and IV (20-35 mm) size class. Food mass was similar in females and males. Differences were, however, noted in the ingested food mass between fertile and infertile females which was smaller in the former. In all studied sites the snails fed mainly on detritus which constituted from 70 to 90% of food mass ingested of all individuals. Detritus abundance in studied habitats might result in using it by snails as obligatory though low-energetic food source. Detritus contributed more to the food of viviparids from Zegrzyński Reservoir and from oxbow lakes, slightly less - to the food of those from outlet stretches of rivers and from the Narew River. Algae contributed from 5% (Zegrzyński Reservoir) to 15% (the Narew River) to the food mass in snail guts. Apart from diatoms, green algae, dinoflagellates and chrysophytes, also cyanobacteria were found in snail food mass. Green algae (46% of all algae) and diatoms (37% of all algae) constituted the largest part of viviparids algal diet in the reservoir. The share of chrysophytes and dinoflagellates made about 10%. More diatoms (up to 48%) and less green algae (up to 25%) were found in snails from outlet stretches of rivers. Guts of snails from the Narew River contained mainly diatoms (over 50%) and green algae (30%). Gut content of snails from oxbow lakes was dominated by green algae (50% of all algae) and diatoms (35% of all algae). Inorganic matter in a form of mineral particles contributed least to the food of snails in the reservoir and in oxbow lakes (ca 5%) in comparison with snails from other sites. No food of animal origin was found. In general, it can be stated that the amount of food mass ingested and its composition differed rather slightly among studied habitats, seasons and individuals.

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Egg number-female body weight relationship in freshwater snail (Viviparus viviparus L.) population in a reservoir

Jakubik B.

Polish Journal of Ecology

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2007

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Vol. 55, nr 2

325-336

EN

Studies on the fecundity of V. viviparus were carried out in the years 1990-1994 in selected littoral sites of the Zegrzyński Reservoir (Central Poland) (60 km long, mean depth ca. 3.5 m, maximum depth at the dam up to 9 m, mean retention time from 1 to 15 days) and in outflow stretches of its tributaries. All sites were dominated by fertile females (i.e. having embryos) that lived in aggregations. Mean numbers of females ranged between 30 and 250 ind. m[^-2]. Females of III (shells 12.1 - 20.0 mm wide and 12.1 - 25.0 m high) and IV (20.1 - 25.0 mm width and 25.1 - 35.0 mm height) size class dominated. The embryos were noticed in females of II (8.1 - 12.0 mm width and height of the shell), III and IV size class and mean number of embryos per female was from 0.9 to 6.7, from 1.1 to 9.6 and from 2.0 to 9.1 for II, III and IV class respectively. Analysis of embryonic development revealed the presence of three growth stages in oviducts of females: the oval, transparent egg capsules called the youngest embryos), egg capsules with visible contour of a shell (called medium embryos) and snails with a shell (the oldest embryos). Embryos in a form of oval, transparent egg capsules and snails with developed shell dominated in particular size classes in analysed sites. Analysis of the correlation coefficient showed significant positive relationship between the mean sum of embryos and shell height and width, and dry weight of female's body and shell weight. Most significant correlation was found between dry body weight and mean number of embryos. The number of embryos in particular growth stages was also related to biometric indices as shown by the analysis of correlation coefficients. The number of oldest embryos (fully developed snails with a shell) increased with the increase of shell height and width. Female.s dry body weight, on the other hand, was best correlated with the youngest growth stage of embryos (oval, transparent egg capsules). Described relationships indicate the importance of the size of V. viviparus females for reproductive success and for survival and "condition" of young snails.

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Year-to-year stability of aggregations of Viviparus viviparus (Linnaeus 1758) in littoral zone of lowland, rheophilic reservoir (Central Poland)

Jakubik B.

Polish Journal of Ecology

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2003

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Vol. 51, nr 1

53-66

EN

The aggregations of V. viviparus were observed in the littoral of Zegrzyński Reservoir (Central Poland), and in the outfalls of its tributaries. They were present over five years of studies (1990-1994), at the same sites. The densities of snails in the aggregations differed among the sites (from over 800 to 500 ind. m-2 in the reservoir itself), and showed seasonal changes with maximum in summer, and minimum in spring and fall. Swarming of the snails was related to the environmental changes and biology of this species. Tendency to form bigger snail conglomerations in the mouth sections of the rivers results from continuous inflow of organic matter being food supply for these organisms.