ii ABSTRACT OF THE DISSERTATION SPECIALIZED RELATIONSHIPS BETWEEN ACTIVE BACTERIA AND THEIR ENVIRONMENT

The question as to which environmental factors select for or influence the resident and active community within the global ocean is still unclear. While general trends have been established in overall community response to natural forces and the impact of particular environmental parameters on biodiversity, little has been done to examine how certain species react to environmental stimuli and how the percentage of metabolically active species correlates to the ambient conditions. This research aimed to address these understudied areas and provide insight into how particular alterations in the physical, chemical, and biological environment relate to species composition and activity. More specifically, this work utilized molecular techniques, such as 16S and 18S ribosomal RNA analysis, to track how changes within the active and resident bacterial populations correlate to changes in environmental drivers. By narrowing the focus to two widely spaced locations, a New Zealand Fjord and a Caribbean river plume, and then evaluating these relationships in the laboratory, it was our hope to find patterns in species-specific bacterial activity associated with salinity, DOM, and phytoplankton dynamics in model systems. Results of this work indicate that no single environmental parameter drives the iii diversity of a system and that only a small percentage (< 30%) of the active bacterial population were correlated with the physical/chemical/biological parameters measured in our field studies. Furthermore, this data indicates that the appropriate parameters are not currently being measured to determine the regulatory force on the abundance and activity of the microbial population