SEASONAL DYNAMICS OF NUMBERS AND BIOMASS OF RIVER SNAILS (MOLLUSCA, VIVIPARIDAE) IN WATER BODIES OF POLISSIA

Abstract

The seasonal dynamics of population density of Viviparus viviparus and
V. contectus is studied in 2011. The river snails are active from March to OctoberNovember. However, in the last years their activity has been recorded in
December due to the abnormally warm climatic conditions of late autumn.
Their numbers and biomass are highest in summer and minimum in spring and
autumn. During the period of activity, the population density and biomass of
V. viviparus range from 5 to 118 specimens/m2
and from 8 to 265 g/m2
,
respectively. For V. contectus, these characteristics range from 7 to
76 specimens/m2
and 22 to 278 g/m2
.
In populations of V. viviparus, which prefers rivers, the hatchlings make up 7–
10 % of all snails in April, and maximum numbers and biomass are observed in
June. In V. contectus, which mostly inhabits stagnant waters, the hatchlings make
up 10 to 15 % of all snails in April, and maximum population indexes are recorded
somewhat later in July. There is a strong correlation (r=0,89−0,95) between the
water temperature and studied characteristics of river snail populations.
The ongoing global warming of the Earth caused changes in population
ecology of Viviparidae. They remain active for longer periods: the snails wake
from the hibernation earlier in spring, and migrate to winter later than before.
Key words: Viviparidae, numbers, biomass, seasonal dynamics.