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

Jakubik B.

Polish Journal of Ecology

2009

Vol. 57, nr 2

321-330

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.

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

Jakubik B.

Polish Journal of Ecology

2007

Vol. 55, nr 2

325-336

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.