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2 Oceanological and Hydrobiological Studies

2 2008

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Diversity and vertical distribution of planktonic ciliates in a stratified mesotrophic lake: relationship to environmental conditions

Mieczan T.

Oceanological and Hydrobiological Studies

2008

Vol. 37, No.1

83-95

The density and biomass of planktonic ciliates significantly differed between sample sites in a deep, mesotrophic lake, with the lowest numbers in the hypolimnion and the highest in the epilimnion. The community composition varied greatly with depth. Oligotrichs dominated in the epilimnion, where prostomatids and peritrichs were also important components of the community. The density of oligotrichs and peritrichs decreased in the metalimnion, and they were absent from the hypolimnion. In the deep metalimnion the most abundant groups were prostomatids, haptorids and scuticociliates. In the hypolimnion, the ciliate community was dominated by scuticociliates and heterotrichs. In the epilimnion and metalimnion a significant positive correlation was observed between ciliate numbers, chlorophyll a and heterotrophic flagellate density. In all three zones the number of ciliates was most strongly correlated with water temperature, concentrations of total organic carbon (TOC), total phosphorus (Ptot) and bacterial density, whilst in the hypolimnion there was a significant correlation between ciliate numbers and the dissolved oxygen concentration.

Diet composition and prey selection of vendace Coregonus albula in the mesotrophic, temperate Lake Ostrowite (Northern Poland)

Kakareko T., Napiórkowski P., Kozłowski J.

Oceanological and Hydrobiological Studies

2008

Vol. 37, No.1

57-68

Lake Ostrowite is a mesotrophic lake in Northern Poland 280.7 ha in area and 43 m deep at its deepest point. To study vendace (Coregonus albula L.) diet in the lake, fish and zooplankton were sampled at two stations on 28-29 April, 15-16 May (fish only), 28-29 July and 15-16 August 2004. Fish were caught by gill netting, while zooplankton was collected from the whole water column by means of a Ruttner sampler (5 × 2 dm3). In total 91 vendace specimens were analysed, of which 64.8% had non-empty alimentary tracts. In the April and May samples Copepoda were the most numerous prey, while Daphnidae dominated the diet in the July- and September-caught fish. Planktonic Chironomidae pupae were also an important dietary item in the April-caught fish. Cladocerans, especially from Daphnidae family, were positively selected by vendace whilst copepods were not. Large predatory cladocerans, Leptodora kindtii, and the non-indigenous Bythotrephes longimanus were consumed in substantial quantities by the July- and Septembersampled fish, with the vendace feeding more intensively on the L. kindtii than on the B. longimanus.