Growth, Mortality, Fecundity, Biomass and Productivity of Four Lake Populations of the Prosobranch Snail, Viviparus Georgianus

Abstract

Studies were carried out on natural populations of the freshwater prosobranch snail, Viviparus georgianus, located in 4 mesotrophic lakes in upstate New York. Viviparus are among the dominant members of the benthic fauna at the second trophic level in these localities. A growth survey involved regular sampling for measurements of growth, fecundity, mortality, and biomass production. Viviparus georgianus were variable in ♀ life span, with 2 populations having a 36—mo maximum life and the remaining 2 populations having a 28—mo maximum life. Maximum life span of ♂ ♂ was similar in all populations at 21—22. Analyses of growth and biomass production as organic carbon and total nitrogen were utilized to estimate standing crop biomass leading to productivity rates, and of changing C:N ratios during growth and reproduction. Productivity ranged from 0.911 to 8.303 mg C/(m 2 °day). The ♀ portions of the populations were °5x as productive as the ♂ portions. The lower life span, growth rates and productivity of ♂ ♂ are believed to be linked to increase ♂ mobility during the breeding period, with subsequent decrease in filter—feeding during spring primary productivity. Reproduction in V. georgianus was iteroparous and vivaparus, with a gestation time of °9 mo. Fecundity varied seven—fold between the populations, with reproductive output paralleling the productivity rate. Fecundity of ♀ ♀ approximates a 1:3:2 ratio for 1—, 2— and 3—year—old ♀ ♀ respectively. Reproductive output with respect to ♀ age is discussed.