DISTRIBUTION OF HYDROBIID SNAILS IN RELATION TO SALINITY, WITH EMPHASIS ON SHELL SIZE AND CO-EXISTENCE OF THE SPECIES (original) (raw)

Abstract

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.

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