AME 55:209-218 (2009)  -  DOI: https://doi.org/10.3354/ame01302

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 µm s^–1). Vorticella convallaria (Peritrichia) remained about 45% of the observed time in a contracted state at >2600 µm 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 µm 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 µm 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 µm 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.

KEY WORDS: Ciliate morphotypes · Biofilm · Flow velocity · Boundary layer · Motility · Rheotaxis