A project undertaken at the Centre for Sustainable Aquatic Ecosystems, Murdoch University, and supervised by A/Prof Alan Lymebery.
Freshwater mussels are vital components of aquatic ecosystems because they maintain water quality, increase productivity and transfer energy and nutrients between the water column and sediments. Unfortunately, freshwater mussels are also one of the most endangered groups of organisms in the world, and their decline is having a detrimental effect on the functioning of aquatic ecosystems.
Carter’s freshwater mussel (Westralunio carteri) is the only species of freshwater mussel found on the west coast of south-western Australia. The range of the species has declined by almost 50% in the last 50 years, mainly because of secondary salinisation and drought. Further losses of natural populations appear inevitable in a drying climate in which water flow in south-west rivers has decreased by up to 75% since the 1970s.
New strategies are required to prevent the extinction of Carter’s freshwater mussel. We propose that artificial water bodies, such as farm dams, disused mining pits and canals or drains, which often retain water throughout the dry season, can be used to establish refuge populations of mussels, sourced from existing natural populations in the same catchment. For the owners or managers of water bodies, the mussel populations will provide improved water quality, such as reduction in algal and bacterial loads, and increased water aeration. For conservation purposes, these artificial populations will provide an insurance against extinction and a source of recolonization following habitat restoration in natural waterways. For this strategy to be successful, the owners or managers of artificial water bodies need confirmation that mussels will improve water quality, and conservation management agencies need assurance that artificial population sizes are sufficient to maintain genetic diversity in the long-term.
In this project, we directly addressed these two issues. First, we surveyed artificial water bodies and found that they could support self-sustaining populations of Carter’s freshwater mussel, at densities similar to that found in natural river populations. Second, we determined the factors necessary for artificial / water bodies to support high densities of mussels, principally the presence of native fishes, which act as hosts for mussel larvae, and riparian shading, which reduces water temperature. Third, we estimated that mussels have a filtration rate of 14/ml/g/hr and spend almost 95% of their time filtering water; which allows us to calculate the potential of a mussel population to remove organic matter, such as algae and bacteria, from a water body of a given size. Finally, we tested our calculations in a semi-natural situation and determined that mussels did indeed significantly reduce the algal load in a body of water.
The results obtained in this project have had two important outcomes. First, they have led to further funding to address additional questions which have arisen as part of this study; in particular the effect of environmental factors on mussel filtering capacity, and the potential role of artificial water bodies to support other aquatic organisms, as well as freshwater mussels. Second, they have been used to help inform conservation planning for Carter’s freshwater mussel by the Western Australian Department of Biodiversity, Conservation and Attractions.