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Freshwater mussels

monkey-faced mussel

Yes, that is a mussel pictured above. Read on to find out what sort it is and what it does for you. When most people think of mussels, they think of the sea. If you have ever collected wild sea mussels yourself, you probably have memories of standing knee deep in sea water prying them off rocks. More and more people nowadays eat farmed mussels, un-memorably purchased shrink wrapped from a supermarket. But there are mussels that live in fresh water too and they perform wonderful services for us.


What are freshwater mussels?

Freshwater mussels (referred to as FW mussels from now on) are bivalve molluscs that live mostly live in flowing water. A few species live in still water.  They have no head, eyes, ears, or appendages⁠⁠, just a muscular "foot" that they use for burrowing.  Adult mussels tend to bury themselves in sediment at the bottom of the river bed. This makes them very inconspicuous to human observers, and visually, it downplays their vital role in the community.  Although similar in appearance to marine mussels, the two groups have been separated for at least 200 million years and have very different biology.1

There is a wide diversity in the size of FW mussels from a few millimetres across to almost 20 centimetres across and shells vary in shape and colouring.

Mussels’ names echo their diverse shell shapes and are equal parts poetry and cartoon. Common names for mussels include the threehorned wartyback, sheepnose, fatmucket, heelsplitter, rabbitsfoot, pistolgrip, pigtoe, monkeyface, and snuffbox. The image at the head of this page is a monkeyface.

Mussels are slow growing and may not reach adulthood for 5 - 6 years. Some species live to over 100 years under favourable conditions.

FW Mussel distribution

There are thought to be about 1000  different species of FW mussel distributed all over the world except for Antarctica, although knowledge of African and South American species is very patchy, so there may be many more. North America is the region with the highest diversity of FW mussels.

FW Mussel reproduction and ecology

FW mussels reproduce sexually with males releasing sperm into the water which fertilizes the eggs of females. They then enter into the next phase of their life cycle as parasitic larvae. They grow on and feed from fish gills until they reach the stage of a viable juvenile form.  Then they detach from the gills, and start living independently. This means that their survival and distribution is linked to the distribution and mobility of their host fish, but they do gain the advantage of increased opportunities to colonise regions otherwise unavailable to them.  Some species can only live on the gills of a very restricted range of fish; others can be less selective in their range of hosts. FW mussels have evolved various means of delivering their larvae to the host fish including clamping their shells around a fish's head, or developing a pseudo-appendage that looks like a small fish to act as bait.



water filtration

Mussels filter large volumes of water to extract their food, removing nutrients, algae, bacteria and organic detritus from the water.

An adult mussel is a powerful, durable and efficient water filter inside a hard shell. It can filter up to 35 to 40 litres of water daily (10 gallons), removing algae and organic matter and transforming water from cloudy to clear so that bottom-dwelling plants get more light. A mussel builds its own tissues from the material it filters, locking up nitrogen, phosphorus and carbon for decades. And it deposits its waste on the streambed, providing nutrients for bottom-dwelling algae, insects and other invertebrates, which, in turn, feed fish.2

FW mussels are doing the heavy lifting in terms of keeping streams, rivers, creeks etc clean and potable. They lessen the cost of human intervention to clean up  fresh water.3

Food web integrity

Mussels themselves are food for other species e.g. rakali and platypus in Australia, e.g.  otters and raccoons in North America. Also their empty shells are utilised by other organisms such as crustaceans and fish for protection and anchoring. Decaying shells  slowly release calcium, phosphorous, and nitrogen to be used by other parts of the ecosystem.


Mussels are often used as environmental indicators as they are sensitive to pollution, as shown by striations on their shells. Also, they are very good indicators of historical conditions as they are a stable feature of a particular location for a long time due to their immobility once they have settled in a spot.

Food and raw material services

Freshwater mussels are commonly eaten in some parts of the world. They are protein rich and  a good source of vitamins and minerals.

Freshwater mussels were an important source of food for Indigenous Australians. Middens containing large numbers of mussel shells are widespread alongside rivers and lakes. First Nations people also used mussel shells as tools.1

In the USA, overharvesting of mussels by non-indigenous people happened in repeated waves as people saw the opportunity to exploit FW mussels for easy money. This applies to the use of mussel shells to make buttons, and exploitation by the pearl market e.g. FW mussels were used to make 40 million buttons  in 1916. If you are interested in these historical stories, the FMCS website Freshwater mussels has interesting accounts.

Summary of services provided for us

  • Water filtration
  • Carbon, Nitrogen and Phosphorus sequestration
  • Environmental indicator of ecosystem health
  • Food for other organisms in the ecosystem
  • Food for humans
  • Raw materials - mother of pearl, button manufacture, tools

Threats to the services?

Freshwater mussels are one of the most endangered groups of animals on the planet, with 47% either extinct or threatened with extinction. Yet we hear almost nothing about the extinction crisis they face.

Habitat modification/destruction

  • damming rivers
  • silting due to creek side grazing, tilling practices, land clearing
  • changing the course of waterways for human convenience
  • construction of structures such as bridges and weirs

Climate change

Climate change is altering the thermal profile of waterways. This may also  be accompanied by  low oxygen levels. Mussels have poor mobility capabilities so migration is not an escape strategy. In times of drought, extra stress is imposed on streams if water is pumped out of the river for drinking or irrigation purposes.

One of the most serious threats to freshwater mussel populations in Australia is climate change. Reduced rainfall has resulted in a dramatic reduction of water flow. In south-western Australia, for example, water flow has decreased by around 70% since the 1970s and climate change models predict at least a further 25% reduction by 2030.4

Chemical poisoning

Mussels can be poisoned by relatively low levels of ammonia, a form of nitrogen common in waters polluted with sewage or agricultural runoff. Creeks may also be contaminated with chemicals such as human and veterinary medications and dumping of materials. Juveniles and adults can have different susceptibilities.

Invasive aquatic species

Weeds introduced by human disturbance can be a major problem for FW ecosystems.  One prominent example is Giant salvinia (Salvinia molesta), a highly invasive, free-floating aquatic fern, originally from Brazil. It outgrows native vegetation, and causes the water to become anoxic which will kill the mussels.

Zebra mussels Ironically, it is one of their own that is a very serious threat to endemic FW mussels. For native mussels, infestation of zebra mussels has had near catastrophic effects. They increase in numbers faster than non-native mussels and attach to almost any hard surface, including native mussels. They reproduce so fast and in such abundance that the native mussels' movement, feeding, and reproductive behaviors are stifled. One mussel was found to have over 10,000 zebra mussels on it.

What can we do to retain these services?

A freshwater mussel is the opposite of a charismatic species...People don’t see it and don’t know what it’s doing.2

Freshwater ecosystems are not well protected by laws and research into them is not well funded. There are not many protected areas for FW mussels and associated assemblages of organisms. They need protection particularly from habitat disturbance caused by human activities e.g. discharge of dangerous wastes into waters, dam permits and bank degradation by livestock, channel dredging regulations

We need more research data and more legal protections for these organisms which render such valuable services.


Dig deeper

  1. Freshwater mussels [] []
  2. The hidden strengths of freshwater mussels [] []
  3. Ecosystem Services Provided by Native Freshwater Mussels []
  4. They live for a century and clean our rivers - but freshwater mussels are dying in droves []
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