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UBC Theses and Dissertations

An investigation of the growth and feeding responses of oligotrich ciliates to food types and concentrations : an approach to assessing the potential of marine planktonic ciliate blooms Montagnes, David J. S.


Planktonic ciliates consume small phytoplankton and can be important in the transfer of carbon through food webs. This study examined the impact of clonal ciliate populations on short term algal blooms. Numerical and functional responses (growth and grazing rates with varied food concentration)were established for 5 marine planktonic ciliates and were used in a model to examine predator-prey dynamics of ciliates and 8 Am algae. The ciliates Strombidinopsis acuminatum, Strobilidium spiralis, Strobilidium sp., Strombiclium acuminatum, and Strombiclium capitatum were isolated from British Columbian waters and maintained in culture. Ciliates were fed the flagellates Isochrysis galbana, Chroomonas sauna, Rhodomonas lens, and the diatom 7halassiosira pseudonana, individually or in combinations. Numerical responses were obtained by keeping ciliates in semi-continuous culture, measuring growth rates and fitting them to a modified Michaelis-Menten function; this provided both growth and mortality rates. Species specific differences existed in numerical response parameters. Functional responses were measured by observing the uptake of fluorescently labeled C. sauna or 5 it m beads. This was a poor method: when measured grazing rates were compared to those predicted by a bioenergetic formula, the measured rates either over or underestimated predicted rates by several fold. Functional responses were determined using 1) the bioenergetic formula Ingestion =(growth+respiration)/assimilation efficiency, and 2) volume specific respiration rates. Ciliate functional and numerical responses from this and other studies were compared, and 3responses were established. These were used in a model which simulated ciliate-algal population dynamics in a non-steady state, where ciliates and copepods encountered a patch of water with a defined initial algal concentration. The model indicated: 1) ciliates bloom over 10-20 d, when copepods are rare (<1 L4) and algae are initially abundant (>103 mL4); 2) ciliate blooms can provide 40-50% of the carbon available to copepods, but when copepods are abundant and initial algal levels low, ciliates are not an important carbon source; 3) under "typical" conditions (103 algae mL4,1 copepod L4), ciliates are a link to copepods, but primary production is low; 4) bloom dynamics and carbon flow through the food web are dependent on the ciliate species present. In general, ciliates maybe, under transient conditions, important as both links and sinks of carbon, but under "typical" coastal conditions, ciliates are not important components of food webs.

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