Investigating the drivers and control of filamentous algae and restoration of aquatic plants in the Coorong

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Project Partners:

CSIRO, Flinders University, The University of Adelaide, and Other

Research Theme:



Project Overview

Ruppia tuberosa (Ruppia) is a keystone species for the southern Coorong – contributing to maintaining water quality and trapping sediment while providing habitat for invertebrates and fish, and food for waterbirds. Beginning in late spring and continuing over the summer, excessive filamentous algal growth in the Coorong negatively impacts on Ruppia growth and seed production throughout the system, particularly in the southern Coorong, with flow-on effects for the Coorong ecosystem (Collier et al. 2017). These impacts are exacerbating the long-term recovery of the Coorong ecosystem following the large-scale losses of the Ruppia community in the Coorong throughout the Millennium Drought despite successful translocation efforts (Collier et al. 2017). The current state of the previously robust Ruppia community, has been described as being in a vulnerable state requiring significant effort to restore resilience and multiple ecological functions (Brookes et al. 2018). Field observations over the last 4-5 years suggest that the southern Coorong has remained in the Hypersalinity–High Nutrient state (Figure 1 – upper right panel).

Figure 1. Conceptual diagram summarising alternative states for the southern Coorong based on observed ecological conditions (from Collier et al. 2017).

The dominance of filamentous algae impacts ecological functions of the southern Coorong through:

  • filamentous algal mat forming species gaining an advantage over Ruppia through the combined, complex interactions of nutrient availability, salinity, water temperature and water level (Collier et al. 2017)
  • increased prevalence of filamentous algae, compared to Ruppia, altering nutrient cycling away from relatively stable fixed carbon (i.e. Ruppia) persisting throughout the season to more rapid dynamic trophic cycling typical of eutrophic systems (filamentous algae and micro-biota)
  • algae accumulating on shorelines, forming mats that prevent shorebirds from accessing food resources from within mudflats
  • filamentous green algae forming mats at the water surface shading plants and entangling Ruppia flowers resulting in them breaking away from stems, leading to Ruppia failure to set seed
  • failed reproduction of Ruppia contributing to a depleted seedbank and lowered resilience of the population, which affects the invertebrates, fish and waterbird for which it provides food and/or habitat
  • the breakdown of algae that accumulates on shorelines reducing oxygen levels within the sediment, affecting the invertebrate communities, and thus food for key fish and waterbird populations (Dittmann et al. 2017, Paton et al. 2017, Collier et al. 2017)
  • filamentous green algae creating a barrier at the water’s surface impeding foraging by birds (Paton et al. 2018).

Progress Update and Key Findings

The primary focus for this Aquatic Plant and Algae Component is to support management of the Coorong to shift the system from algae-dominated to a Ruppia-dominated habitat, improve water quality and restore the ecological function associated with an aquatic plant dominated state.

The Component will support the management of the Coorong by investigating how to:

  • avoid the permanent loss of ecological values of the Coorong South Lagoon
  • restore the ecological values of the Coorong South Lagoon
  • create an ecosystem that maintains the ecological values under climate change.

To achieve this, a series of more specific questions are being addressed in this research including:

  • What are the effects of salinity, temperature and nutrients on algal and aquatic plant growth and can the use of management levers be optimised to create habitat (as determined by salinity, temperature and nutrients) that favours aquatic plants (including Ruppia) over algae?
  • Does reducing the algae levels improve Ruppia abundance and distribution in the Coorong?
  • What are the interactive effects of salinity, water level, temperature and nutrients on algal growth and mortality?
  • How can algae be managed to support recovery of aquatic plants (e.g. remove inhibitors to reproductive success)?
  • When, where and under what conditions have algal blooms occurred in the Coorong historically and what were the drivers of these blooms (to be used to forecast probability of algal blooms in the future)?
  • Can filamentous algal blooms be physically managed to prevent threats to Ruppia reproduction
  • What is the current extent of the aquatic plant community (including Ruppia) in the Coorong?
  • What are the other microbiota that are dominant in the Coorong and do they represent a large proportion of the organic nutrients in the total southern Coorong system?
  • What is the current condition of Ruppia in the southern Coorong, including distribution, amount and seed bank status and how does this relate to the ecological character conditions and other requirements under the Ramsar convention and EPBC legislation?
  • Are conditions, or habitat suitability, for Ruppia in the Coorong able to be managed to a range of options that lead to recovery of the system, specifically a return to aquatic plant dominated rather than algal boom dominated, without intervention?
  • What are the critical elements of management interventions that will provide a long term, large scale, successful restoration of Ruppia communities in the southern Coorong?

Project Impacts

Research Outputs

Distribution and seasonality of the Ruppia dominated aquatic macrophyte community and filamentous algae in the southern Coorong

Healthy Coorong, Healthy Basin: 3. Aquatic Plants and Algae

A restoration strategy for the Ruppia Community of the southern Coorong

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 growth of aquatic macrophytes (Ruppia tuberosa spp. and Althenia cylindrocarpa) and the filamentous algal community in the southern Coorong

Project News