Differential depth distribution among freshwater pulmonate snails subjected to cold temperatures

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Abstract
The depths chosen by four species of basommatophoran snails in response to temperatures varying between 15 and 1 °C were compared under controlled conditions in the laboratory. Three species (Lymnaea stagnalis (L.), Physa gyrina Say, and Helisoma trivolvis (Say)) moved to greater depths as temperatures declined, whereas Stagnicola elodes (Say) showed the opposite trend. The average depth exhibited by each species over this range of temperatures was significantly (P < 0.05) different, suggesting some form of segregation. Stratification was most apparent at 1 °C when S. elodes was most surficial followed, in order of increasing depth, by L. stagnalis, P. gyrina, and H. trivolvis. The ecological significance of these results is discussed.