Is the difference in population dynamics of Daphnia galeata in littoral and pelagic areas of a long-term biomanipulated reservoir affected by age-0 fish predation?

We analysed population dynamics of Daphnia galeata in littoral and pelagic areas of the long-term biomanipulated Bautzen reservoir during spring and e arly summer of two consecutive years. Simultaneously, consumption of the ag e-0 fish community was estimated by means of a bioenergetics model. As a co nsequence of biomanipulation, the abundance of adult planktivorous fish in Bautzen reservoir is low and the interactions between underyearling percids and Daphnia are a key process in the food web of this water. In both years , density and mean size of D. galeata were markedly lower in littoral than in pelagic areas, whereas no differences were found in the size at maturity and clutch size. However, the lower proportion of adults in the littoral z one resulted in drastically reduced birth rates, which could not explain th e strong fluctuations in Daphnia abundance. These findings were consistent during the whole investigation period. Daphnia consumption by age-0 fish wa s markedly higher in the littoral than in the pelagic zone and accounted fo r up to 50% and even 100% of Daphnia mortality in this habitat. However, du e to gape-size limitation, age-0 fish did not feed on daphnids before June. We conclude that besides underyearling percids older planktivorous fish co ntribute to the suppression of D. galeata in the littoral zone of Bautzen r eservoir and that recruitment of daphnids in this habitat mainly takes plac e via (active or passive) immigration.