FRESHWATER MUSSELS: by Kaye Proudley
One species that we did not include (not that we could have fitted in any
more!) in the new JARR Project’s brochure - Mammals, Reptiles &
Aquatic Fauna, was the Freshwater Mussel, which occurs in some of our
local rivers and streams, so I thought I’d tell you about them here.
A member of the invertebrate family, Freshwater Mussels are large,
brown or black bivalve molluscs which live in, sometimes dense beds
containing thousands of shells, in shallow, fairly swift flowing streams,
usually with a sandy, gravelly, substrate. Mussels can live from 3 to
anywhere up to 40 years. They burrow using their strong muscular foot,
then lie buried with only the posterior of their shell margins exposed,
through which their short siphons extend into the stream flow to siphon
water to feed. This they do by filtering water to remove algae,
zooplankton and other detritus (and remove pesticides, heavy metals
and other pollutants from our precious freshwater as a by-line.) This
makes them perhaps not very attractive for us to eat BUT it does make
them very useful as biological monitors. Aboriginals used to eat them;
water rats and platypus eat them currently.
Top - Cucumerunio novaehollandiae. Bottom - Alathyria profuga. By Kerry Wilson
These mussels are similar in appearance to marine mussels but have
been separated for about 200 million years and have a very different
biology.
You might well be pushed to find them in the rivers – it’s not like they
are pretty creatures disporting themselves in an attractive way trying to
catch our attention …. more that they look very similar to the algaecovered rocks they may be lying beside! Some local residents of course
have found them washed up after storms flood our rivers, when the
mussels get dislodged and end up in storm detritus on the banks.
Australia has at least 18 species all belonging to one family (Hyriidae)
and are found only in Australasia.
South America contains close
cousins to our species.
But what we lack in species richness, we make up for in uniqueness –
their larvae known as glochidia, and measuring a tiny quarter of a
millimetre (that’s about as big as a grain of sand!) attach to the gills of
some species of freshwater fish like smelt, gudgeon, bass and even
non-indigenous species like eastern gambusia - but never carp or
goldfish - where they metamorphose, to emerge somewhere more farflung, as juvenile mussels. That way they can distribute themselves
around much more successfully than an adult mussel stuck at home in a
riverbed could. The dependence of mussel glochidia on freshwater fish
means that they are also very dependent on the health of the fish as well
as on the health of the waterways.
Female mussels produce huge numbers of glochidia but few find a fish
host and even fewer survive to maturity. After detaching from their fish
hosts, the immature mussels burrow into the streambed where they will
stay, growing rapidly for a few years.
They are one of the most ‘‘at-risk’’ groups of fauna in the world,
disappearing at an alarmingly unrecognized rate.
Velesunio ambiguous, Flood Plain Mussel by Ashley of Moree, NSW
Already some eastern Australian mussels have disappeared from many
streams. At least two Australian species qualify for conservation listing
(like the Glenelg River Mussel [Hyridella glenelgensis,] which has been
recently listed as Critically Endangered under the Victorian Flora and
Fauna Guarantee Act 1988 and the Commonwealth Environment and
Biodiversity Conservation Act 1999 (EPBC Act.) Some of the reasons
they are threatened in some parts of Australia are –
-
Loss of catchment & streamside vegetation & the shading effect
that disappears along with the vegetation
Channel erosion and sedimentation
Increased nutrient loads in runoff
Invasive water plants
Invasive species like Carp
-
Salinity
Cattle trampling and overgrazing
Habitat rehabilitation, species recovery plans and follow-up monitoring
are critical to allow these sensitive species to flourish. The trouble is,
many of these freshwater mussels occur in habitat on private land and
we don’t know too much about them. These plans need to be led by
expert scientists, government and communities working together.
Species found in Sth East Australia according to http://keys.lucidcentral.org/keys/lwrrdc/public/Aquatics/aemoll/html/key_to_s.htm
Alathyria pertexta, Alathyria profuga, Velesunio wilsonii, V. ambiguous
(Flood Plain Mussel), Cucumerunio novaehollandiae, Hyridella
glenelgensis, H, narracanensis, H. drapeta, H. australis and H. depressa.
To that end, I would be very interested to hear from any local people
who are aware of them in streams and rivers on their land - who
remember them from childhood or know of them currently, or have an
opinion on whether the freshwater mussels are doing well or declining
or whatever is the case. I would also appreciate knowing the names of
local species and photos if you have them too please.
Sources:
- Article in ‘The Conversation’ by Dr Michael Klunzinger of the School of
Veterinary & Life Sciences at Murdoch University, W.A.
- Brian J. Smith - Tasmanian Field Naturalists. The Tasmanian
Naturalist (2005) 127: 49-53
Hyridella glenelgensis – collection specimen from Australian Museum, Sydney, NSW