Date of Award


Document Type

Open Access Thesis

Call Number

QR106 .W74 2010

Degree Name

Master of Science (MS)



First Advisor

Lisa Moore, PhD

Second Advisor

Theresa Theodose, PhD

Third Advisor

Jeffrey Walker, PhD


The distribution and abundance of marine picoplankton populations in the Patagonia Large Marine Ecosystem (PLME) were quantified from samples collected during the COPAS08 (Coccolithophores of the Patagonian Atlantic Shelf Cruise) that took place in Austral summer from December 2008 to January 2009. Twenty seven stations were sampled at 5 depths for picophytoplankton and heterotrophic bacterial abundance using flow cytometric analysis and DNA nucleic acid staining. Additional samples were taken from a carboy incubation experiment to quantify the effect of increased CO2 concentrations on the picoplankton community. Results showed that cyanobacteria dominated the picoplankton biomass throughout the PLME, particularly at lower latitudes closer to the influence of subtropical waters, (between 38 and 48S latitude) which included stations 7- 10 corresponding to the Brazil current region of warmer, sub-tropical, oligotrophic waters, and at stations 20, 28,30,32 and 54 in deeper waters off the shelf-break; whereas picoeukaryotic abundance was greater at station 5 and across the shelf-break stations 15 - 18; 44, 48 and 50, at higher latitudes south of 45S. Cyanobacteria showed a positive correlation with temperature and a negative correlation with total dissolved inorganic nitrogen, whereas there was little relationship between picoeukaryotic abundance and temperature or nutrients. Heterotrophic bacteria showed a slight positive correlation with both temperature and cyanobacteria abundance. The results of two carboy incubation experiments to measure the response of marine phytoplankton assemblages to different pCO2 levels indicated that some members of the picoeukaryotic populations exhibited significant increases in abundance during the experiment. Cyanobacteria and heterotrophic bacterial populations exhibited an increase in abundance over 72hrs, during the first experiment with water obtained from outside the coccolithophore bloom (at station 5), however this response showed no clear relationship with elevated CO2. Picoeukaryotes obtained significantly higher populations at 24 and 72hrs during the second experiment conducted with water from within a coccolithophore bloom at station 24 but similarly, the response did not arise from the increasing levels of CO2. The measured populations within each carboy experiment reflected different phytoplankton communities with unique taxonomic composition. Our analyses of the picoplankton within the hydrographic regions and during carboy experiments provide a baseline indication of picoplankton population distribution and abundance and present an important contribution to understanding the biological community within the PLME, a region of significance to understanding global biogeochemical processes.



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