Diel Vertical Migration in Daphina Iumholtzi (Sars)

Abstract

ABSTRACT In light of recent studies which suggest that the extreme morphology of Daphnia lumholtzi (Sars) does not effectively deter all vertebrate predators, we sought to determine if this species exhibits behavioral responses that, may minimize planktivory by fish. Zooplankton vertical migration patterns were monitored in Newton Lake (Jasper County, Illinois, USA) by sampling the same site every 4 h for 48 h at 0, 2, 4, 6, and 8 m depths. Single factor ANOVAs revealed that Daphnia lumholtzi, Diaphanosoma brachyurum, Daphnia pulex, mature calanoid and cyclopoid copepods, and Chaoborus punctipennis were migrating vertically, but rotifers and copepod nauplii were not. The occurrence of diel vertical migration in D. lumholtzi suggests that extreme morphological features possessed by this species may not deter all predators. Temporal overlap in vertical distribution of D. lumholtzi and Chaoborus punctipennis indicates that vertical migration in this species is not an effort to avoid the only invertebrate predator in Newton Lake capable of consuming D. lumholtzi. Rather, because North American planktivorous fish have been shown to be able to prey upon D. lumholtzi despite its large spines, we believe that vertical migration behavior in D. lumholtzi is a response to the presence of fish.