Population dynamics of the marine planktonic ciliate Strombidinopsis multiauris: its potential to control phytoplankton blooms (original) (raw)

1999, Aquatic Microbial Ecology

The growth, grazing, and cell volume of Strombidinopsis multjaurls, a large (-100 pm) coastal planktonic cil~ate, IS affected by food concentration and temperature. Using growth and grazlng data, we modelled small-scale bloom dynam~cs between the clliate and ~t s prey. Growth expenments were conducted at 13°C on S. niultiauris fed the 10 pm d~noflagellate Gymnodiniurn simplex; changes in cell numbers and cell volume were monitored. Ingestion rate was measured by 3 methods (uptake of fluorescently labelled latex beads, heat-killed, fluorescently labelled G nmplex; and I4C-labelled G. simplex). Growth rate vprsus food concentration followed a rectangular hyperbolic response, with a maxlmum of p = 0 6 d ' above 104 prey ml-l (480 ng C ml-l), below 1.3 X 10"l-' (62 ng C ml-l), mortality occurred. Cell volume followed a rectangular hyperbolic response to food concentration, and showed a doubling in size between zero and maxmum prey levels. Grazing rate initially ~ncreased with food concentration and was then inhib~ted at levels >10"rey ml-l. The cil~ate ~ngested 14C-labelled live prey at higher rates than either dead or artificial prey at subsaturating concentrations; above saturating concentrations, ingestion rates were similar for the 3 prey types. The maximum observed grazlng rate was 35 prey cihate ' h-' Growth rate and cell volume were measured under steady-state conditions at 9 temperatures between 3 5 and 22°C: clliates died at 3.5 and 5"C, growth rate increased hnearly to a maximum of p = 0.9 d-l at 15"C, did not change between 15 and 20°C, and decreased at 22°C. Cell volume ~ncreased between 5 and 10°C and decreased between 10 and 22°C. The population dynamlcs model revealed that the ciliate was able to control the dinoflagellate population. Over the 20 d model simulation, virtually no predator-prey cycle occurred when prey growth rates were p < 0.2 d-' As prey growth rate was increased bloom dynamics became apparent, with a minunum duration of-10 d for a bloom to begin and end at a prey growth rate of p = 0.65 d-l. During these simulated blooms ciliates reached maxlmum levels of 35 cells n~l-' , and prey reached levels of 1.7 X 104 cells ml-', slmilar to numbers found in a typical coastal bloom. Our data and model suggest that ciliates and their prey produce episodic, short-term blooms, and we recommend that these events be evaluated more carefully in the field and be incorporated into models. KEY WORDS. Blooms. Cell volume. Grazing rate. Growth rate. Microzooplankton. Mortality rate. Ohgotnch ciliate. Plankton. Temperature response