Graduate Thesis Or Dissertation

Population dynamics of Skeletonema costatum in high dilution rate chemostats

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  • A chemostatic system was developed for the long term studies of population dynamics of chain forming diatoms. Vessel volume rather than flow rate was varied in these systems to obtain different growth rates at steady state in systems with an equal capacity to produce. Population level responses to high dilution rates were examined for Skeletonema costatum both in long term steady state and under non-steady state conditions. Development of populations were observed from small innocula through steady state dilution rates approaching the maximum growth rate of the population. Populations were characterized in terms of particulate carbon and nitrogen, particle numbers and volumes, particle size distributions, and the relationship of production and specific growth rate to biomass. Qualitative observations were made on cell dimensions, morphology, and bouyancy. Four phases of growth were identified in some or all of the systems: selection phase in which population concentrations declined, but significant changes in population characteristics occurred; exponential phase in which populations increased in a uniform and density-independent fashion; transition phase in which adjustments were made in population characteristics; and, finally, steady state in which populations were stable. Selection phase was observed when small innocula were placed in high dilution rate systems or when steady state cultures were transfered to higher dilution rates. Those cultures experiencing selection phase showed changes in physical cell dimensions and in nutrient cell size. Physical cell dimensions and nutrient cell size and their relationship to growth rate are discussed. The work of Caperon (1968) is examined for similar selectional effects. A method using curves of nutrient per cell versus residence time of a particle in a chemostat is suggested to separate selection and dilution rate effects in dynamic systems. A model summarizing the ides of nutrient reservoirs is suggested.
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