engleski

Development of ciliate community on artificial substrates associated with vertical gradients of environmental conditions in a karstic lake

The composition of ciliate communities, their abundance and biomass were studied on glass slides exposed in the epilimnion (1 m), metalimnion (9 m) and hypolimnion (18 m) in the karstic barrage Visovac Lake (SW Dinarid, Croatia). After one-month exposure periods from May 1995 to February 1996, mean ciliate biomass decreased with depth (at 1 m 54 μ g cm-2, at 9 m 37 μ g cm-2 and at 18 m 28 μ g cm-2), whereas the mean population density was relatively uniform (675 Ind. cm-2 at 1 m, 592 Ind. cm-2 at 9 m, and 678 Ind. cm-2 at 18 m). Sessile forms (peritrichs and suctorians) were dominant during all exposure periods and at all three depth layers. Omnivorous ciliates were dominant in the epilimnion, whereas in the metalimnion and hypolimnion bacterivores and carnivores were most abundant. Ciliates inhabiting artificial substrates in the epilimnion had two temporal peaks of density and biomass: in June and in October. In the deeper layers these maxima appeared one or two months later. Seasonal changes in ciliate biomass and community and trophic composition were associated with changes in thermal stratification and vertical oxygen gradients as important abiotic parameters, periphyton biomass as food source, and the tufa deposit determining the properties of substrate.

ciliates; periphyton; tufa deposit; lakes

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