Date of Award

Summer 2014

Document Type


Degree Name

Master of Science (MS)


Ocean & Earth Sciences


Ocean and Earth Sciences

Committee Director

Margaret R. Mulholland

Committee Member

Alexander Bochdansky

Committee Member

Harold G. Marshall

Call Number for Print

Special Collections LD4331.O35 O96 2014


Concentrations of atmospheric CO2 are expected to double by year 2100 as a result of anthropogenic activities. Under elevated CO2 conditions, cyanobacteria may reallocate energy from active accumulation and transport of dissolved inorganic carbon (C) required for photosynthesis to other growth processes. Stimulation of cyanobacterial production on the Western Florida Shelf in the Gulf of Mexico (GOM) could lead to improved nutritional status for the toxic, mixotrophic dinoflagellate Karenia brevis that utilizes newly fixed N2 from co-occurring diazotrophic cyanobacteria and consumes unicellular cyanobacteria via grazing for growth. Culture studies performed by other researchers on the climate induced physiological changes in the GOM diazotroph Trichodesmium erythraeum have revealed that this ecologically important cyanobacteria fixes dinitrogen (N2) and grows at higher rates under elevated pCO2 compared to present day conditions. Research performed to determine impacts of elevated pCO2 on primary production and diazotrophic physiology in other important cyanobacterial groups, including coastal Synechococcus cf elongatus, Lyngbya spp. and unicellular diazotrophs is limited, but all currently contribute to bioavailable N pools fueling K. brevis blooms. This thesis explores the connection between elevated CO2 and stimulation of production and N2 fixation in cyanobacteria to better estimate the nutritional status of GOM phytoplankton, especially K. brevis, under future climate conditions.

Incubation experiments were performed using cultured populations of coastal S. cf elongatus and T. erythraeum, and natural populations of Trichodesmium spp., Lyngbya spp. And a mixed phytoplankton assemblage from the GOM to estimate the impact of elevated pCO2 and/or elevated temperature on their N and C physiology. Cultured populations experienced stimulation in C fixation at high pCO2 and N2 fixation was stimulated in T. erythraeum. Natural populations of Trichodesmium spp. Also experienced elevated rates of C and N2 fixation at high CO2, but significant pCO2 stimulation of production and N2 fixation was not observed in Lyngbya spp. and the mixed phytoplankton assemblage. The supply of available N and provision of prey species available to fuel K. brevis production is likely to increase under future climate conditions because dominant cyanobacteria increase primary production rates and N2 fixation under elevated pCO2 and/or temperature conditions.


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