Bacterivory by pelagic choreotrichous ciliates in coastal waters of the NW Mediterranean Sea

Abstract

Ability of natural assemblages of pelagic ciliates to ingest bacteria was tested using fluorescently labeled bacteria (FLB) prepared from in situ bacterioplankton. Ciliate bacterivory was analysed both in freshly collected samples from the mouth of Villefranche Bay, NW Mediterranean Sea, and in 50 mu m screened water held in 201 plastic carboys in the laboratory. In various experiments, from 23 to 97% of the choreotrich assemblage ingested FLB added in tracer amounts (2 to 4 x 10 super(5) FLB/ml), with average clearance rates ranging from 14 to 308 nl/cell/h. Very little ingestion of FLB observed for other types of ciliates, e.g. didinids and hypotrichs, seen in the samples. Specific clearance rates (on the basis of FLB ingested) of individual morphological types of ciliates was on the order of 0.6 to 4 x 10 super(4) body volumes/h for larger choreotrichs, and up to 2 x 10 super(5) body volumes/h for the smallest choreotrichs.