Homeostatic interactions between the benthic microbial communities and the waters of a hypersaline lake, Lake Hayward, western Australia

In hypersaline Lake Hayward, photosynthesis by benthic microbial communities (BMCs) is normally sufficient to supersaturate the bottom water with dissolved oxygen during periods of stratification. The BMCs are dominated by cyanobacteria such as Cyanothece in the permanently inundated centre of the lake and by Microcoleus in the seasonally desiccated littoral. However, after an unusually dry year in 1987, the salinity increased to 260 g L-1 and gypsum precipitated throughout the lake. The turbidity generated was sufficient to obscure the benthos completely despite the shallowness of the lake (<2 m). As a result, the BMCs were greatly altered and the amount of oxygenic photosynthesis was reduced. During the following winter (1988), during stratification the bottom water became anoxic and sulfurous. However, during the next few years the BMCs reestablished and were able to again supersaturate the bottom water with oxygen. Limnological and microbiological changes that occurred in this period are described and it is concluded that the BMCs function as a strong homeostatic mechanism allowing long-term stability of the present limnological characteristics of Lake Hayward. Therefore, the development of the BMCs represented a significant step in the ontogeny of the lake, which now differs distinctly from nearby lakes that do not contain such BMCs.