AME 20:167-181 (1999)  -  doi:10.3354/ame020167

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

David J. S. Montagnes1,*, Evelyn J. Lessard2

1Port Erin Marine Laboratory, School of Biological Sciences, University of Liverpool, Port Erin, Isle of Man IM9 6JA, British Isles
2University of Washington, School of Oceanography, Box 357940, Seattle, Washington 98195-7940, USA

ABSTRACT: The growth, grazing, and cell volume of Strombidinopsis multiauris, a large (~100 μm) coastal planktonic ciliate, is affected by food concentration and temperature. Using growth and grazing data, we modelled small-scale bloom dynamics between the ciliate and its prey. Growth experiments were conducted at 13°C on S. multiauris fed the 10 μm dinoflagellate Gymnodinium 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. simplex; and 14C-labelled G. simplex). Growth rate versus food concentration followed a rectangular hyperbolic response, with a maximum of μ ~= 0.6 d-1 above 104 prey ml-1 (480 ng C ml-1); below 1.3x103 ml-1 (62 ng C ml-1), mortality occurred. Cell volume followed a rectangular hyperbolic response to food concentration, and showed a doubling in size between zero and maximum prey levels. Grazing rate initially increased with food concentration and was then inhibited at levels >104 prey ml-1. The ciliate ingested 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 grazing rate was 35 prey ciliate-1 h-1. Growth rate and cell volume were measured under steady-state conditions at 9 temperatures between 3.5 and 22°C: ciliates died at 3.5 and 5°C, growth rate increased linearly to a maximum of μ ~= 0.9 d-1 at 15°C, did not change between 15 and 20°C, and decreased at 22°C. Cell volume increased between 5 and 10°C and decreased between 10 and 22°C. The population dynamics 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 μ < 0.2 d-1. As prey growth rate was increased bloom dynamics became apparent, with a minimum duration of ~10 d for a bloom to begin and end at a prey growth rate of μ = 0.65 d-1. During these simulated blooms ciliates reached maximum levels of 35 cells ml-1, and prey reached levels of 1.7 x 104 cells ml-1, similar 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 · Oligotrich ciliate · Plankton · Temperature response

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