Cyanobacteria in benthic microbial communities in coastal salt lakes in Western Australia
John, Jacob; Hay, Melissa; Paton, Jennifer
Microbial communities dominated by cyanophytes and diatoms are the predominant primary producers in the hypersaline coastal salt lakes of Western Australia. Two such lake systems were investigated with a focus on cyanobacteria. Rottnest Island, located 18 km from the west coast of Perth, Western Australia, has salt lakes with salinity up to 200 g L−1. Lake Clifton, located 120 km south of Perth, is a salt lake with a salinity range of 30 to 79 g L−1, well known for the largest array of living thrombolites in the Southern Hemisphere. Both these lake systems have extensive benthic microbial communities (BMC) in the form of algal mats dominated in biomass by cyanobacteria. The BMC in Rottnest Island's salt lakes have higher diversity and biomass of cyanobacteria than diatoms, whereas the Lake Clifton mats have higher diversity of diatoms but lower diversity of cyanobacteria. In both systems cyanobacteria dominate in biomass. The microbial communities directly associated with thrombolites in Lake Clifton differ in composition and thickness from non-thrombolites benthic microbial communities. The latter are massive and in recent years (2002 and 2007) become dislodged and float during summer-autumn. This is associated with fish death. Scytonema, identified as the dominant cyanobacterium in microbial communities associated with the thrombolites in the 1980s, is no longer observed. Instead there is a filamentous cyanobacterium forming a tight network - a Phormidium species, whereas coccoid cyanobacteria form the bulk of the benthic algal mats in Lake Clifton. Stalked diatoms such as Brachysira aponina and several species of Mastogloia dominate the benthic mats in Lake Clifton. The salinity has doubled in Lake Clifton in the last 25 years. Species of Aphanothece, Oscillatoria, Microcoleus, Spirulina, Schizothrix and Gloeocapsa are the common cyanobacteria in the BMC of Rottnest Island salt lakes. The composition and abundance of cyanobacteria in both lake systems are explained in terms of possible impacts of changing environment with respect to salinity and nutrients.