DISTRIBUTION OF HYDROBIID SNAILS IN RELATION TO SALINITY, WITH EMPHASIS ON SHELL SIZE AND CO-EXISTENCE OF THE SPECIES (original) (raw)
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A total of 60000 individuals of Hydrobia ulvae, H. ventrosa, H. neglecta and Potamopyrgus jenkinsi were collected from the North Sea to the Baltic. H. neglecta dominated in the Kattegat and tapered off towards the North Sea and the Baltic. H. ventrosa dominated in the Baltic and tapered off towards the North Sea. H. ulvae was the only species in the North Sea. It was also common in the Baltic at 5-6%0 while it was rare in the Kattegat at about 20 %0 salinity. The possibility that H. ulvae constitute an ecotype in the Baltic is discussed. The ratios of shell lengths of co-existing species of' hydrobiids were calculated. The ratio H. ventrosa: H. neglecta, H. ulvae: H. ventrosa, and H. ulvae: H. neglecta ranged from 0.80-1.20, 0.90-1.80, and 0.90-1.80, respectively. The most common ratios were 0.90,1.25, and 1.45, respectively. Ratios calculated from mean shell lengths of all allopatric populations were 0.90, 1.25, and 1.38, respectively. This finding is not in harmony with previously suggested character displacement in hydrobiid snails. The discrepancy is discussed with emphasis on environmental factors, life history, and density of individual species as causes of observed size differences. [1986 J. Hylleberg]
ABSTRACT. Postglacial sequence of migration and extinction has been studied in a boring through 10 m deposits in Jutland, Denmark. The main profile contained freshwater and brackish water fauna in the bottom layer. Hydrobia ulvae was first recorded at -9.75 m. Next H. ventrosa was found together with H. ulvae. Then H. neglecta appeared, and all 3 species co-occurred at -8.75 m. At -4.95 m H. ulvae disappeared but H. ventrosa and H. neglecta were still abundant until a depth of -1.90 m. It is concluded that H. ulvae and H. ventrosa quickly colonized the Littorina Sea while H. neglecta may have arrived somewhat later. H. ulvae has the largest larval shell, especially in the Baltic, and H. ventrosa the smallest larval shell of the 3 species. The ecological significance of two markedly different shell forms of H. ulvae is discussed. Postglacial hydrobiids are compared with recent specimens of the 3 species. [1988. J. Hylleberg].
ZooKeys, 2013
Karucia sublacustrina a new species of freshwater snails (Hydrobiidae, Gastropoda) is described based on material collected from Skadar Lake (Montenegro, Albania). The new species belongs to monotypic genus Karucia gen. n. The shell morphology and body shape of the new genus resembles Radomaniola Grossuana Radoman, 1973, from which it differs in the larger shells with relatively slim and a slightly, but clearly shouldered body whorl. The number of gastropods from Skadar Lake basin tallies now 50 species. The adjusted rate of gastropod endemicity for Skadar Lake basin is estimated to be 38%. By compiling faunal and taxonomic data we also aim to provide information of relevance as to conservation efforts.
2012
The specimens of the freshwater snail Radix auricularia collected from Southeastern part of Bulgaria during the cold period as a whole were with mean shell height of 3.7 mm. During spring and summer it was similar, 3.3 mm. The ratio of the size groups was more equally spread during cold seasons rather than in warm ones. The variation index during cold seasons is about seven times higher than in the warm ones (Var = 13.1 and 2.14, respectively). On the five plant species the gastropods had different mean shell heights. For C. demersum it was 3.4 mm (min-max = 1.4-15.8 mm), and for E. canadensis 7.9 mm (min-max = 2.4-14.6 mm), M. spicatum it was 2.8 (minmax = 2.4-3.4 mm), P. natans 3.9 (min-max = 1.1-9.0), P. pusillus 4.8 (min-max = 3.1-8.2).
Character displacement and coexistence in mud snails (Hydrobiidae)
Oecologia, 1975
Populations of coexisting and of allopatrically occurring species of hydrobiid snails (Hydrobia ulvae, H. neglecta, H. ventrosa and Potamopyrgus ]enkinsi) have been studied in 90 localities within three different areas. When H. ventrosa coexists with H. ulvae they show character displacement, i.e., the average body size of the former is smaller and that of the latter is larger. When these species live alone they are of approximately the same size. It is shown here that the size ratio between the coexisting species usually found (1.3-1.5) allows stable coexistence based on food particle size selectivity alone. Variation in the degree of character displacement from locality to locality is explained by different degrees of genetical isolation of the populations. Coexisting H. ventrosa and H. ulvae have shorter, more well-defined periods of reproduction than they do when they occur alone. H. negIecta is larger than coexisting H. ventrosa and smaller than coexisting H. ulvae. Due to the patchy distribution and the fluctuating populations of this species, and due to the fact that pure H. neglecta populations are rare, data on this species are difficult to interpret. Potamopyrgus ]enkinsi shows a different food particle size selection than the Hydrobia spp. of identical sizes. Competitive interactions between P. ]enkinsi and coexisting Hydrobia spp. are therefore probably weak. In accordance with this, P. ]enkinsi does not show character displacement when coexisting with, e.g., H.ventrosa.
2011
The specimens of the freshwater snail Physella acuta collected from Southeastern part of Bulgaria during the cold period as a whole were with mean shell height of 5.7 mm. During spring and summer it was more than twice lower, 2.3 mm. The ratio of the size groups was more equally spread during cold seasons rather than in warm ones. The variation index during cold seasons is about eight times higher than in the warm ones (Var = 3.96 and 0.58, respectively). On both plant species the gastropods had similar mean shell heights. For C. demersum it was 4.8 mm (min-max = 2.5-8.9 mm), and for E. canadensis 7.2 mm (min-max = 3.6-10.0 mm).
FRESHWATER SNAILS (MOLLUSCA: GASTROPODA)OF BULGARIA: AN UPDATED ANNOTATED CHECKLIST
The list of freshwater gastropods of Bulgaria, with data on their distribution, ecology and conservation status, was based on a critical overview of all available sources and unpublished materials. The total number of freshwater snail species hitherto recorded from Bulgaria is 120. Three species are regarded as extinct, two species were found only as subfossil remains. The most diverse families are Hydrobiidae (67 species), Planorbidae (15), and Lymnaeidae (11). The remaining families are represented by 1 to 4 species. Zoogeographical, ecological and conservation data are discussed.