Date of Award

12-2012

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Oceanography

Advisor

Lee Karp-Boss

Second Committee Member

Mary-Jane Perry

Third Committee Member

David Townsend

Abstract

Production of allelopathic chemicals by the toxic dinoflagellate Alexandrium fundyense is one suggested mechanism by which this relatively slow grower outcompetes other phytoplankton, particularly diatoms. Despite well documented allelopathic potential of Alexandrium spp., the potency is variable. To further characterize allelopathic effects of A. fundyense on diatoms in the Gulf of Maine, I studied growth and nutrient acquisition by the chain-forming diatom Thalassiosira sp. in the presence and absence of allelochemicals. Thalassiosira cells, upon exposure to filtrate of A. fundyense cultures exhibited “bleaching” and both growth and nutrient utilization ceased for up to 4 days compared to controls. Results from this study support the existence of chemically mediated interactions, although the relatively high A. fundyense concentrations required to elicit a response suggest a greater role of such interactions in bloom maintenance than initiation. The magnitude of the effect was dependent on filtrate concentration and Thalassiosira cell size. Thalassiosira cultures that had undergone cell enlargement via sexual reproduction were less sensitive to A. fundyense filtrate, recovering earlier and showing less “bleaching.” This difference in allelopathic effect did not appear to be related to either the total biovolume or total surface area of experimental cultures but cultures of cells with higher surface area/volume showed higher effects. These results demonstrate that competitor cell size, iii independent from taxonomy, is likely to be important in shaping the outcome of allelopathic interactions. The findings presented here suggest a potential ecological impact of diatom cell size reduction and sexual reproduction that has not yet been described and that may be important in determining diatom survival and success.

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