Microbial community composition of the southern Coorong including evaluating seasonal variation and sediment, water column, aquatic macrophytes and filamentous algae as substrates for microbial growth.

The aquatic macrophyte community of the Coorong consists of mixed populations of Ruppia tuberosa and Althenia cylindrocarpa and another unresolved species of Ruppia. For the purpose of this report, these mixed populations have been termed the ‘Ruppia Community’. An almost complete decline of the Ruppia Community as a result of the impact of the Millennium Drought (2001-2010) in the Coorong included the loss of seed banks. The recovery of the Ruppia Community has been gradual with the number of sites occupied by plants increasing over the past decade. Recovery of the Ruppia Community has been impeded most strongly in the Coorong South Lagoon because of the hyper-eutrophic state of the southern Coorong. The Coorong South Lagoon is dominated by algal blooms, including mat forming filamentous algae that physically disrupt the aquatic macrophytes’ ability to flower and set seed. The microbiota associated with algal blooms and the hyper-eutrophic conditions are very poorly understood in the Coorong, the unique set of environmental characteristics of this environment make understanding the microbiota critical to interpretation of the biological status of the system.

The South Australian Government’s Healthy Coorong, Healthy Basin (HCHB) program’s Trials and Investigations (T&I) project includes studies on the aquatic plants and algae (Component 2) undertaken between July 2020 and April 2022. This investigation of the microbial communities present in the Coorong South Lagoon, and in the southern parts of the North Lagoon, improves our understanding of pelagic and benthic microbial dynamics in relation to water quality and promoting (or not) the growth of the Ruppia Community...