Microbial Processes, Structure and Diversity along the Natural Salinity Gradient of the Coorong Lagoon, South Australia; A Model for Anthropogenic Impact

Author: Kelly Newton

Newton, Kelly, 2012 Microbial Processes, Structure and Diversity along the Natural Salinity Gradient of the Coorong Lagoon, South Australia; A Model for Anthropogenic Impact, Flinders University, School of Biological Sciences

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Aquatic microbial communities control the movement of energy, matter and elements through the biosphere and thereby mediate biogeochemical cycles, species diversity and evolution. The aquatic microbial food web describes the interactions between viruses, archaea, bacteria, phytoplankton, zooplankton and the organic/inorganic matter that mediate these cycles. Members of the microbial food web are controlled by the "top–down" pressure of mortality and the "bottom–up" physiochemical nature of the environment. Of the physiochemical parameters salinity is a major "bottom–up" controlling factor. As aquatic environments are affected by anthropogenic alterations in salinity, the microbial community will respond in turn and potentially impact on these globally important community interactions and biogeochemical cycling. This thesis investigates the processes, diversity and structure of the microbial community of the Coorong estuary, lagoon and lake system in South Australia. The Coorong is of high ecological importance and exhibits a large continuous salinity gradient which was used to examine the influence of salinity on the microbial community. Additionally, this thesis investigates the trade–off between cellular resource utilisation and potential energetic gain. The results demonstrate that salinity has clear and well defined impacts on the taxonomic and metabolic potential of the bacterial community, and on viral community diversity and production. However, when determining how "top–down" pressures alter with salinity, the impact is less clear and it is likely that the impact on both the predator and prey communities plays a role in mortality. This thesis additionally illustrates that the bacterial community can gain an energetic and resource advantage by expending energy on flagellum production, confirming theoretical predictions and highlighting a seldom investigated component of energy use and movement through aquatic ecosystems. This thesis provides the first detailed insight into the diversity, structure and processes of the microbial community in the Coorong and shows that while some effects of anthropogenic environmental change, specifically on the structure of the microbial community, can be somewhat anticipated, microbial processes and interactions between "bottom–up" and "top–down" pressures are more complex and more research is required in order to successfully anticipate and mediate anthropogenic change.

Keywords: bacteria,viruses,phytoplankton,microzooplankton,the Coorong,food web,salinity,top-down,bottom-up,energy,flagella,bacterial taxonomy,bacterial metabolism,viral morphology,community diversity

Subject: Biological Sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2012
School: School of Biological Sciences
Supervisor: Professor Laurent Seuront