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 Vlllefranche Bay, NW Mediterranean Sea, and in 50 pm screened water held in 201 plastic carboys in the laboratory. In various experiments, from 23 to 97 "h of the choreotrich assemblage ingested FLB added In tracer amounts (2 to 4 X 105 FLB ml-'), with average clearance rates ranging from 14 to 308 nl cell-' h-' Very little ingestion of FLB was observed for other types of ciliates, e.g. did~nids 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 104 body volumes h-' for larger choreotrichs, and up to 2 X 10' body volun~es h-' for the smallest choreotrichs. We estimated that it would b e possible for choreotrichs < 15 pm in size to grow at a rate of about 0.5d-' on a n exclusive diet of bacteria at a concentrat~on of 10' bacteria ml-l, but that the larger cdiates were obtaining less than 15 % of their food rations a s bacteria. These data are the first direct evidence that some pelagic ciliates can be consumers of heterotrophic bacterioplankton in meso-to oligotrophic seawater.

Biological response to iron fertilization in the eastern equatorial Pacific (IronEx II). III. Dynamics of phytoplankton growth and microzooplankton grazing

“…These rates are reasonable relative to experimental results with labeled prey (Lessard & Swift 1985, Sherr et al 1989, and they are conservative in making no allowance for grazing by mixotrophs. It is instructive to note that the 100-fold increase in diatom biomass early in the bloom does not require a similar increase in grazer biomass to bring diatoms under control.…”

Ciliategrazing on picoplankton in a eutrophic reservoir during the summer phytoplankton maximum: A study at the species and community level

“…However, the FLC addition constituted up to 40% of picocyanobacteria abundance at the beginning of September when abundances of picocyanobacteria already dropped below 2.5 x lo4 ml-l. For the rest of the study, the use of the tracer technique was impossible due to low picocyanobacteria abundance. Thirty-milliliter subsamples for protozoan enumeration and tracer ingestion determinations were taken 0,3,6, 10,20, and 30 min after tracer addition and fixed by adding 0.5% of alkaline Lugol's solution immediately followed by 2% borate-buffered Formalin (final concn) and several drops of 3% sodium thiosulfate to clear the Lugol's color (B. F. Sherr et al 1989).…”

“…On the other hand, increasing cvidcncc from marine systems indicates that some ciliate taxa arc voracious consumers of bacteria Sherr 1987, E. B. Sherr ct al. 1989;B. F. Sherr et al 1989).…”

Growth kinetics of the omnivorous oligotrich ciliate Strombidium sp

“…We focus on nonloricate ciliates because they are I Present address: Hydrology Research Centre, 11 Innovation Blvd., Saskatoon, Saskatchewan S7N 3H5. Supported by NSF OCE 88-12 123 and NOAA Sea Grant NAS9AA-D-SC;138 usually more abundant and comprise greater biomass than the loricate tintinnids (Beers and Stewart 1969;Gifford 1985;Sherr et al 1989).…”