Date of Award

8-2012

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)

Department

Marine Science

Committee Chair

Donald Redalje

Committee Chair Department

Marine Science

Committee Member 2

Kjell Gundersen

Committee Member 2 Department

Marine Science

Committee Member 3

Karen Orcutt

Committee Member 3 Department

Marine Science

Abstract

Bacterioplankton growth and metabolic activities are a vital component in structuring marine and estuarine ecosystems. In this study, bacterial production (BP) was investigated at two separate stations in the western Mississippi Sound (MS). One was an inshore site outside of the Bay of St. Louis and the other site was located in the transition zone (offshore) between the MS and Mississippi Bight, just south of Cat Island. Bacterial production (BP) was analyzed using the addition of 14C leucine to natural water samples. In addition, samples were augmented with algal exudates in order to investigate BP based on uptake of extracellular organic carbon released by a diatom (Chatoceros gracile) and a chlorophyte (Oocystis sp.). The addition of diatom photosynthetic extracellular release (PER) versus chlorophyte PER was assessed to see the affect on BP rates as well. Bacterioplankton production was measured using the leucine incorporation microcentrifuge procedure (Kirchman 2001). These analyses were conducted from July 2011 through December 2011. The highest bacterioplankton production rates were found in July and lowest in December, with BP values ranging from 14 μg C l-1 d-1 to 425 μg C l-1 d-1. There was no significant difference between bacterial production rates between stations but a strong seasonality was found between summer and fall months. Spearman's rank analysis indicated that BP was correlated positively with chl a, in situ temperature, and silicate, but no significant correlation was found with inorganic nutrients. There were no significant differences between PER enhanced BP rates and non-augmented BP. In addition, there were no significant differences in BP when enhanced by diatom or chlorophyte PER. These results suggested that BP in the western Mississippi Sound did not appear to be limited by inorganic nutrients and labile dissolved organic matter (DOM). Phytoplankton were found to be an important labile substrate for bacterial production in this region. Based on the high BP results, heterotrophic bacteria may be of greater trophic importance than what was thought before in the western MS.

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