Feeding behaviour of two planktonic freshwater ciliates coexisting during spring time in the eutrophic Belauer See (Bornhöveder Seenkette, North Germany)

AbstractIn spring 1991, we investigated the development of the planktonic community of a eutrophic lake (Belauer See, North Germany), focusing on the feeding behaviour of Vorticella rhabdostyloides and Tintinnidium fluviatile, the two most abundant ciliate species in the pelagic zone of this lake during spring. Experiments on the uptake of fluorescently labelled particles in different size classes and fluorescently labelled bacteria and algae permitted the determination of the importance of those kinds of food. Vorticella rhabdostyloides ingested particles about 1.0 μm and 3 μm long and autotrophic picoplankton (APP). Tintinnidium fluviatile preferred particles 0.5 μm to 1.0 μm and 5.0 μm long, APP and diatoms in the genus Nitzschia. Ingestion rates ranged between 100 and 120 particles h−1 for each Tintinnidium fluviatile and 60 to 230 particles h−1 for each Vorticella rhabdostyloides. APP, bacteria, centric diatoms and nanoprotozoans were evaluated as foods for both ciliates. Tintinnidium fluviatile was found to exert a strong short-term control on picoplankton (rs = −0.941, n = 6, p < 0.05) and small centric diatoms (rs = 0.700, n = 6, p < 0.05). The different diets of both ciliates may explain the coexistence of both species during spring