Morphological variation in Daphnia cucullata Sars with progressive eutrophication of a polymictic lowland reservoir

Morphological variation in Daphnia cucullata Sars was studied from 1994 to 2001 when fast increasing water trophy of the Siemianowka Reservoir was related to high TP and chlorophyll concentrations. During this period, D. cucullata biomass, as well as its contribution to the total cladocerans biomass clearly decreased. We found that among the six morphological parameters analyzed in D. cucullata, body length, height of the head and length of the tail spine had a tendency to decrease. The maximum values of these traits and carapace length also decreased. The morphology of D. cucullata appeared to be influenced by factors such as food availability, fish predation and an exclusive presence of D. cucullata among Daphniidae species. Increased water mixing in the reservoir may have also affected the changes in the head inclination of D. cucullata.