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Living Lightly column

Are mussels the champions of our rivers?

By Jonathon Howard

I think mussels should be given an award. Afterall, mussels are amazing biofilters, they play a crucial role in keeping rivers healthy, and are an important part of the food web of our inland fisheries. Yet mussels are dying in the thousands, each mass death event brings those endangered molluscs species closer to extinction. Tragically, these events rarely get noticed.

So how often do you encounter a mussel these days?  Compare this to accounts of the abundance and ubiquity of river mussels throughout the Murray-Darling Basin that were recorded in the diaries of inland explorers like Oxley, Hume and Hovell, Mitchell, Sturt and Hawdon and the reminiscences of early settlers. Near present-day Albury, in 1824, William Hovell noted that “the lagoons are literally crowded with wild ducks, and in the muddy bottom near the banks, is plenty of muscles”.   Indeed, until recently mussels were considered so abundant that New South Wales fisheries scientist David Stead thought that they could be a commercial industry.

Freshwater mussels are sedentary and long-lived animals, so their ecology is intrinsically linked to their aquatic habitat. There are 18 species of freshwater mussels in Australia, and at least three of them occur locally.

One of the most serious threats to our freshwater mussels is climate change. Reduced rainfall means there is a dramatic reduction of water flow. This loss of flow means as more of our rivers go without water over the dry season, and as these drought conditions are lasting longer, mussels die. Mussels can live for a short time without water by burrowing, but longer and more severe dry spells will kill them.

Unfortunately, if we look at river gauges to see the ‘cease to flow events’ of our tributaries, then we see that water flow has more than doubled the duration of what occurred naturally. For example, the severe drought of 2017-2020, exacerbated the threats caused by decades of over extraction and mis-management of water in the Murray Darling Basin.

And while this particular year has been a time of high water availability, the overall trend of increased drying across the Basin is reducing mussel populations.

The plight of freshwater mussels illustrates a sad reality for our freshwater life. Freshwater ecosystems are incredibly diverse. Despite this, the conservation management of freshwater species lags far behind that of terrestrial or marine species. Freshwater environments are very poorly protected by conservation reserves and, to be frank, we need to consider not just conserving a species, but also what they need to survive if we are to manage the Murray Darling Basin.