Benthic Microbial Communities of Australian Saline Lakes

Abstract

Cohesive benthic microbial communities (BMC) are common in Australian salt lakes. They are dominated by photosynthetic prokaryotes and, less frequently, eukaryotic microalgae. StructuraJ integrity is derived primarily from filamentous prokaryotes or stalked diatoms. The organic matter produced by in situ (or external) photosynthetic CO2 fixation is then decomposed by a series of microbial processes culminating in sulfate reduction and methanogenesis, from which the final carbon degradation products are CO2 and CH4. Degradative processes are most active just below the photic zone but are also interspersed throughout it. BMC are characteristically laminated, reflecting the spatial organization of the various physiological groups present and their interaction with each other and with the physicochemical environment. The totality is a dynamic equilibrium exhibiting steep gradients and striking diurnal fluctuations. Community members must adopt suitable metabolic and behavioural strategies to deal with these and other, less regular, fluctuations in parameters such as salinity and desiccation. Still unresolved are questions concerning the following topics: the quantitative importance of BMC primary production in relation to that of phytoplankton and aquatic macrophytes, the environmental factors promoting formation of BMC and their ability to compete with other primary producers, the quantitative significance of anoxygenic photoautotrophy in BMC, the effect of meiofauna on internal elemental cycling and exchange with the overlying water, and the significance of photoheterotrophy at high salinities.