Detachment and motility of surface-associated ciliates at increased flow velocities

Abstract

Though seldom investigated, the microcurrent environment may form a significant part of the ecological niche of protists in stream biofilms. We investigated whether specific morphological features and feeding modes of ciliates are advantageous for a delayed detachment at increased flow velocities. Three sessile filter feeders (Vorticella, Carchesium and Campanella spp.), 6 vagile filter feeders (Aspidisca, Euplotes, Holosticha, Stylonychia, Cinetochilum and Cyclidium spp.) and 2 vagile gulper feeders (Chilodonella and Litonotus spp.) were studied. A rotating disk on top of the culture medium generated different flow velocities in Petri dishes. All tested sessile species stayed attached at the fastest investigated flow velocity (4100 m s -1 ). Vorticella convallaria (Peritrichia) remained about 45% of the observed time in a contracted state at > 2600 m s -1 . Hence, filtration activity of sessile ciliates seemed to be inhibited at high flow velocities. Among the vagile filter feeders, flattened species which extended more than 60 m into the water column and round species showed the lowest resistance to high flow velocities. Only the vagile flattened gulper feeder Chilodonella uncinata (Phyllopharyngia) withstood flow velocities 2600 m s -1 . All studied vagile species (except the seldom-creeping Cyclidium glaucoma) had a higher displacement rate and showed a positive rheotactic creeping behavior between 300 and 1100 m s -1 . Thus, dispersion and positive rheotaxis might allow vagile species to colonize more favorable habitats and balance the drift caused by the unidirectional flow of water.