The effect of irradiance on production and growth of the marine bloom-forming dinoflagellate Gyrodinium aureolum

Garcia, Virginia Maria Tavano (1989) The effect of irradiance on production and growth of the marine bloom-forming dinoflagellate Gyrodinium aureolum. University of Southampton, Doctoral Thesis.

Abstract

The morphological and physiological responses of cultured cells of the marine dinoflagellate Gyrodinium aureolum grown at various irradiance levels has been investigated. Production rates were determined at a range of light intensities in cultures acclimated to various irradiances using two techniques: the oxygen light and dark bottle method and the ¹⁴C-CO₂ radiotracer technique. Growth rates of G. aureolum have also been measured in cultures grown at various light levels. Gyrodinium aureolum cells showed adaptation to low irradiances by increasing cellular levels of chlorophyll a and reducing cell volume and carbon content. The enhanced pigmentation of low light adapted cells resulted in improvement of both light saturated and light limited rates of photosynthesis in relation to cells grown at higher irradiances. Production rates normalized per chlorophyll a were similar for low and high light adapted G. aureolum cultures. These photosynthetic responses have been identified as an indication of increases in the number of photosynthetic units (PSU's) within the cell, under low light adaptation. A similar set of experiments have been conducted with the marine Chlorophyte Brachiomonas sp. This organism also displayed a number of photoadaptation responses on growth at low light levels and these have been compared with results obtained with Gyrodinium aureolum. Production rates have been measured in natural bloom populations of Gyrodinium aureolum, during a cruise to the Western approaches of the English Channel in July 1987 and an estimation of water column production in the bloom waters attempted. Physiological data obtained with the field populations of G. aureolum are compared with results from culture studies. Finally, a comparison of production measurements obtained with the oxygen flux and the ¹⁴C methods has been made and possible factors influencing the photosynthetic quotient discussed. (DX89575)

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