Life history and population dynamics of the marine cladoceran Pleopis polyphemoides (Leuckart) (Cladocera, Crustacea) in a shallow temperate P?rnu Bay (Baltic Sea)

摘要

The seasonal cycle of parthenogenetic and gamogenetic reproduction modes of the marine cladoceran Pleopis polyphemoides was studied in a shallow semi-enclosed P?rnu Bay, the NE Baltic Sea. Population development of P. polyphemoides was found to be very seasonal with a strong dominance of parthenogenetic females. The gamogenetic reproduction mode occurred almost throughout the whole reproductive season being the most intense during the population abundance peak. The change from parthenogenetic to gamogenetic reproduction was found to be neither influenced by water temperature, salinity nor Chl a concentration. Parthenogenetic fecundity was inversely correlated with water temperature and exhibited a positive relationship with total female body size, but showed no relationship with population density. In general, parthenogenetic females were larger just before or during the population peak. While the population development of P. polyphemoides in spring seemed to be associated with temperature, the drastic decline during the summer was a result of changes in the biotic conditions (predation) rather than in the abiotic environment. Significant fine-scale spatio-temporal variability in the population development and several vital rates of P. polyphemoides observed in the current study calls for caution when interpreting cladoceran multi-annual abundance dynamics from time series obtained with variable and/or low sampling frequencies.