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Date Permissions Signed
Date of Award
Master of Science (MS)
Strom, Suzanne L.
Bingham, Brian L.
Photosynthetic bloom-forming dinoflagellates heavily influence coastal ecosystems worldwide. Many of these protist algae bloom in surface waters during summer when light intensities are highest. Despite its likely role as a top-down regulator of bloom formation, the consequences of high-intensity sunlight exposure on cells are not well understood. This study sought to reveal the effect of high light exposure on cells, keeping in mind the potential consequences for bloom-formation. The suite of conditions under which a species is best adapted to bloom is referred to here as its “bloom niche”. To investigate, I measured physiological changes deemed relevant to bloom health in the two distinct species, Alexandrium fundyense and Heterocapsa rotundata after exposure to high intensity visible light. Ultraviolet radiation (UVR) was eliminated from this study because these wavelengths do not penetrate far in coastal waters due to absorption by dissolved and particulate organic matter. Cells were exposed to high-intensity environmental sunlight (209-1607 µmol photons m-2 sec-1) and compared to control cells which remained at growth culture light levels. After exposure, all cells were returned to growth light levels for recovery. Photosynthetic efficiency (Fv/Fm) was measured periodically throughout the experiment as a proxy for light stress; cells were considered to be stressed when Fv/Fm decreased significantly from levels associated with growth light conditions. Chlorophyll-a (chl-a), average cell volume, cell concentration, and both dissolved and particulate dimethylsulfoniopropionate (DMSP) were measured pre-exposure, post-exposure, and post-recovery. Both A. fundyense and H. rotundata exhibited stress in response to high light exposure. Chl-a and DMSP did not change in response to high light in either species. Swelling took place in H. rotundata cells, resulting in cell lysis in the highest light treatment, but no change in volume or measurable damage occurred in A. fundyense. Grazing experiments with the tintinnid ciliate, Schmidingerella sp. were performed with each species to assess the effect of light stress on predator-prey interactions. No difference in grazing rates were observed, however variance increased with higher light exposure, indicating sunlight may have some effect on prey behavior. The differences in response by the two dinoflagellate species can be explained in large part by differences in cell size and structure. These factors, in concert with environmental stressors, likely shape the bloom niche of a species.
Western Washington University
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Cooney, Elizabeth C. (Elizabeth Colleen), "The Effect of High-Intensity Visible Light on the Bloom Niches of the Phototrophic Dinoflagellates Alexandrium fundyense and Heterocapsa rotundata" (2016). WWU Masters Thesis Collection. 529.