Freshwater mussels of Ontario
Those NFN members who braved the snowy roads
on November 12, 2013, to attend our regular
monthly meeting were treated to a unique
presentation in the history of our club (attested to
by Harry B. Barrett).
Our distinguished guest speaker that evening,
Dr. Todd J. Morris, is a Research Scientist with the
Great Lakes Laboratory for Fisheries and Aquatic
Sciences, Division of Fisheries and Oceans
Canada (DFO). He is currently stationed in
Burlington, Ontario at the Canada Centre for Inland
He has been studying the unionid fauna of
central Canada for the last 19 years. He is currently
a member of the Biodiversity Science section of
DFO and is responsible for leading DFO’s research
program on freshwater mussel Species at Risk. His
research focuses on the distributional patterns of
aquatic organisms and the relative contribution of
biotic and abiotic structuring factors. Dr. Morris is a
founding member and chair of the Ontario
Freshwater Mussel Recovery Team and is a
member of the Committee of the Status of
Endangered Wildlife in Canada (COSEWIC),
Mollusc Subcommittee, the American Fisheries
Society Endangered Mussel Subcommittee and the
Freshwater Mollusk Conservation Society.
The following is an outline of a few highlights of Dr.
WHAT IS A FRESHWATER MUSSEL?
Phylum Mollusca: mussels, clams, snails, slugs, abalone, nautilus, octopus
Class Bivalvia: Bilateral symmetry, 2 hinged shells
Order Unionoida: Parasitic larval stage
Long lived, benthic, burrowing filter feeders. Cycle nutrients, transfer energy within ecosystems, provide habitat and clarify water bodies.
WHAT IS NOT A FRESHWATER MUSSEL?
Fingernail clams (Sphaeriidae)
Zebra and Quagga mussels (Dreissenidae)
Asian Clam (Corbiculidae)
842 recognized species worldwide
302 in North America (2 families)
54 in Canada (2 families)
41 in Ontario (1 family)
In Ontario there are 14 COSEWIC assessed
mussel species, 10 are SARO (Species At Risk
Ontario) listed with 4 awaiting listing decisions.
The life cycle and specific reproduction tactics of
the freshwater mussels can often take strange
In general, the adult mussel releases a cloud of
glochidia (tiny embryos) into the water. The
glochidia need a host fish for the next stage of their
lives. They attach themselves to the gills of the host
where they mature into juveniles – up to 6000
glochidia per gill. The juveniles then release from
the host and drift to the bottom of the water body
where they grow into adults.
The reproduction tactics employed by various
species is where it gets really interesting,
sometimes even bizarre:
1. Broadcast release (Many glochidia, low cost,
low success, host generalists)
The mussel releases huge amounts of glochidia
into the water chancing that a suitable host fish
might come swimming by.
2. Lures – when mussels go fishing (fewer
glochidia, higher cost, higher success rate)
Some mussels have developed lures to attract host
fishes. The fleshy protrusions of their mantle may
take on the appearance of a wiggly worm or a small
fry complete with eye spot and fins (see the above
Some of these mussels release the glochidia first
and then try to attract the host, others lure the fish
first and when the host has arrived it releases the
Another North American mussel (not in Canada)
squirts a stream of water into the air in shallow
water. The water droplets hitting the surface causes
ripples mimicking insect activity attracting the fish.
3. Host capture (few glochidia, high cost, high
The Snuffbox mussel uses this most unusual tactic.
It focuses on host fishes that forage on pebbly
areas, the Logperch, for example. The fish nudges
and rolls the pebbles in search of tasty morsels and
if it happens to nudge a Snuffbox the mussel grabs
hold of the fish with its jagged shell edges. It then
releases the glochidia directly at the fish ensuring a
very high success rate before releasing the host.
Human activity is a major stress factor to the
mussel populations. Historically mussels have been
commercially harvested mainly for their shells –
mother-of-pearl buttons were very popular before
the development of synthetic materials. They were
also harvested for freshwater pearls. Locally,
thousands of mussels were pulled from the Grand
River where the population hasn’t recovered so far.
Disturbances in waterways caused by dams, roads,
agriculture, construction, etc. are other factors in
the decline of the freshwater mussel populations.
Alien invaders, such as Zebra Mussels and Quagga
Mussels attach themselves to the shells of native
mussels in large clumps, the weight of which can
make the host mussel sink into the bottom silt and
suffocate. Fish species like the Round Gobi, a
molluscivore, out-compete native fishes. Introduced
crayfish and the threat of the Asian Carp invasion
present a serious risk to the freshwater mussels by
direct predation or predation of the host fish
The good news is that there are potential areas for
recovery in and around the Great Lakes (according
to a study by the National General Assessment for
Freshwater Mussels of 2004). One such area is the
Inner Bay at Long Point. Other hot spots can be
found at Bruce Peninsula, Lake St. Claire, the
south west end of Lake Erie and a couple of areas
in Lake Ontario.
Additional information can be found on the Ontario
Freshwater Mussel Recovery Team web site.
The Photo Field Guide to the Freshwater
Mussels of Ontario is available at the University of
Guelph Bookstore. Or, download the Canadian Freshwater Mussel
Guide App on the Fisheries and Oceans Canada web site.