Gabriela Post
Bio 205
Project: Zebra Mussel
Scientific Name: Dreissena polymorpha (Pallas, 1771)
Common Name: Zebra Mussel
Linnaeus’s system assigns to each species a two part Latinized name, or binomial. The
first part is the genus to which the species belong. In this case: Dreissena. The second
part refers to one species within the genus: polymorpha. With this system we can group
species.
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Bivalvia
Subclass:
Heterodonta
Order:
Veneroida
Superfamily: Dreissenoidea
Family:
Dreissenidae
Genus:
Dreissena
Species:
D. polymorpha
Binomial name
Dreissena polymorpha
Pallas, 1771
Kingdom: Animalia : Animal Kingdom (taxonomic kingdom comprising all living or
extinct animals)
Phylum: Mollusca (gastropods; bivalves; cephalopods; chitons)
Class: Bivalvia (oysters; clams; scallops; mussels)
Species: Dreissena Polymorpha (inch long mollusk imported accidentally from Europe;
clogs utility inlet pipes and feeds on edible freshwater mussels) Zebra Mussel
www.princeton.edu/perl/webwn
Zebra mussels, Dreissena polymorpha belong to the family Dreissenidae. It is a
freshwater bivalve (shell is composed of two halves) mollusk (relative of clams), found in
North America.
Where do they come from:
Zebra mussels originated in the Balkans, Poland, and the former Soviet Union.
They are native to the Caspian Sea, Black Sea, and Azov Seas of Asia. More
specifically, from the north shores of the Black Sea, in the lower Dneiper or Bug River,
near the Ukranian seaports of Kherson and Nikolyev. They were first discovered in the
Ijral River in 1769. The mussels then spread throughout Europe in canals that were built
in the 18th century. By the 1830’s mussels covered most of Europe and had invaded
Brietain. They first appeared in North America, in 1886-1988 in Lake St.Clair, a small
water body connecting Lake Huron and Lake Erie. Biologists believe that the zebra
mussels were picked up in a freshwater European port in the ballast water of a ship and
were later discharged into the Canadian side of Lake St. Clair. Therefore, they are not
native to North America, but an invasive (introduced) species.
Zebra mussels are not the only freshwater bivalve molluscs that are found in North
America, nor are they the only introduced species. Because of this, it is important to be
able to distinguish between zebra mussels and members of the other two bivalve
superfamilies that occur in North American freshwater habitats. The others being the
Dreissena bugensis and Mytilopsis leucophaeata. These two are most likely to be
confused with the zebra mussel.
Zebra mussels have a concave, or flattened bottom and an acutely angled shell
margin. Both features provide additional stability for the attached mussel. If one places
representatives from all three species on a flat dish, the zebra mussel will be the only one
able to stand upright. The other two mussels have a more rounded bottom.
Habitat
Zebra mussels mostly live in large rivers, lakes, or other bodies of water, such as
the Great Lakes and the Caspian Sea. They flourish in warm weather and inland
waterways in Canada and the United States. Zebra mussels have been known to attach
themselves to places. Some zebra mussels are on the surface in/on docks, pipes, nets, and
valves, but most live two to seven meters deep. Zebra mussels live in fresh and salt
water, although the salt water has not been very salty. The ph of the water zebra mussels
live in is between 7.4 and 8.5. Zebra mussels can be spread by many mechanisms,
including water currents, angler’s bait buckets, and boaters’ bilge and livewells.
Scientists currently believe that most inland lakes become infested by an introduction of
adults rather than veligers (zebra mussel larvae).
Anatomy of the zebra mussel: Zebra mussels are small (<4cm/1.5in) about fingernail
size, but can grow to a maximum length of nearly two inches. The smallest zebra mussel
that has been found was fifteen millimeters, and the largest was fifty millimeters. They
have a hard shell to protect their soft inner body. The shell is made from inorganic and
organic materials that are from the water around the zebra mussels and leftover from the
body. Cold, heat, food, and other things can change the shell production. If there is a
crack or other damage to the shell, the zebra mussel can repair itself if the mantle tissue is
still whole. The intestine gland becomes hyperactive and gives more calcium and other
materials to the cells that are in the mantle and used in the repair process. Their shells
characteristically have alternating light and dark bands (like a zebra) but may be entirely
light or dark. They have a triangular, elongated shape. Zebra mussels have two holes:
the excurrent and incurrent siphon for food. The adult feeds by filtering water through its
siphons, and so zebra mussels, in a small way, clean out water. Zebra mussels also have
a nervous, cardiovascular, and circulatory system.
Ecology
Zebra mussels primarily eat algae. All the foods they eat are rich in calcium.
Because there is no shortage of algae, zebra mussels can’t be hurt by starvation. They
use calcium for many things, including repairing a damaged shell. Zebra mussels have a
great impact on our lives. Some of the things they do are good. They are excellent filters
of water. Because the water gets clearer, the sunlight can get lower and let more plants
live. These plants provide shelter to some fish. Also many native fish, birds, and other
animals eat young zebra mussels. Migratory ducks have changed their flight patterns in
response to zebra mussel colonies. Lake sturgeon feed heavily on zebra mussels, as do
yellow perch, freshwater drum, catfish, and sunfish. However, these native species do
not feed heavily enough on zebra mussels to keep the population under control.
Unfortunately, most of the changes zebra mussels have made to our lives are negative.
Lots of birds have eaten them, gotten sick, and had trouble reproducing. Zebra mussels
may dominate and end the diversity of species, especially native species, because of their
rapid reproduction. When zebra mussels have come in contact with some species, they
have practically killed them. For instance, they almost killed all native Unionid mussels.
Some Unionids were found with 10,000 zebra mussels attached to them. For some
reason, the zebra mussels prefer Unionids as a place to attach themselves to over stones
or dead animals. The mapleleaf clam was also almost wiped out by zebra mussels. Even
though the filtered water brings some positive effects, an adult zebra mussel filters up to a
quart of water per day, which multiplied by millions of mussels means that the mussels
may be filtering all the water in a lake or stream in a day. The animals and algae that are
the food of zebra mussels are also the food for larval fish and other native species, so a
large zebra mussel population may cause a decline in other animals, including native fish,
mollusks, and birds. The filter- feeding activity of zebra mussels causes a related and
frequently dramatic increase in water clarity in infested lakes and rivers.
Zebra mussels can severely affect native clams and mussels by interfering with
their movement, growth, movement, respiration, and reproduction. For example, zebra
mussels can colonize a clam shell to such an extent that the clam cannot open its shell to
eat. Water and environmental agencies are working to protect endangered native species
from the threat of zebra mussels. The primary emphasis of this effort is to education, so
that boaters and fishermen do not inadvertently transfer mussel larvae from one water
body to another. Unfortunately, zebra mussels do not have many predators here because
they do not naturally exist in the North American environment. However, there are many
things that eat the zebra mussel such as sturgeon carp, some diving ducks, and the round
goby (who himself is a nuisance invasive species).Also birds, some crayfish, and other
creatures. All these predators are still not enough to make a dent in the zebra mussel
population.
Reproduction
Zebra mussels usually reach reproductive maturity by the end of their first year.
Reproduction occurs through spawning when sperm and eggs are released into the water.
Mating is encouraged by serotonin, a chemical in their brains. An adult female zebra
mussel may produce between 30,000 to 100,000 eggs per year. Spawning usually begins
in the months from late spring to early summer. The presence of food is the first factor
that contributes to spawning. During this time a large population of algae will produce a
pheromone recognized by zebra mussels. However, temperature is the main factor in
determining when the spawning season begins. The ideal temperature for zebra mussel is
12 degrees Celsius and higher for spawning to start. If by any chance that above
condition does not apply, then spawning may be suspended by that population.
Spawning peaks at a water temperature of about 20 degrees Celsius. A fertilized egg
results in a free swimming planktonic larva called a veliger. This veliger remains
suspended in the water column for 1-5 weeks, and then begins to sink and search for a
stable surface (e.g. rocks, aquatic weeds, water intakes) on which to live, grow, and
reproduce.
Zebra Mussel Veliger
Seaweed
Life Cycle
Zebra mussels live for four to five years. They start by crawling on the bottom of
their habitat, but as they mature, zebra mussels find a more permanent habitat. When
they turn two, zebra mussels begin to reproduce. As mentioned earlier, when it is about
spring/summer, the process starts; Zebra mussels reproduce by broadcast spawning. The
female excretes her eggs and the male fertilizes them with his sperm in the water. The
eggs go through many stages before they become adults. These stages are:
Preshell Larva-the shell has not formed yet
Veliger Stage-the velum develops. Velum is the organelle used for feeding and
swimming.
Straight-hinged Larva-the first time the shell is around the internal organs
Iimbonal Larva-the shell is not transparent anymore
Post-Veliaer Stage-time after the velum has finished developing
Pediveliger-has foot to help it move. The shell is thicker and whiter.
Planti grade-the last stage as a larva. The shell is not round; it has elongated. The
siphons form
Settling Stage-the zebra mussel has finished making organs, gills, and siphons. It is now
a juvenile and will be an adult when it can reproduce. It has also made byssal threads to
attach itself to things. Only about 2% of all zebra mussels survive to adulthood. When a
zebra mussel attaches to a hard surface, it is transformed into the juvenile stage. Then it
develops the double shell which is typical of zebra mussels. A zebra mussel becomes an
adult when it is sexually mature.
Human Impact
Humans have had many influences on the zebra mussels. After all, humans are
responsible for bringing the mussels to the United States in first place. Since then, zebra
mussels have made a significant impact and cost millions of dollars in damage. For the
most part, trailered boats are to blame for the spread of the mussels throughout freshwater
waterways all over North America. Although many companies now have ways to rid
boats of these unwanted creatures, no permanent solution has been found. To find a
solution, scientists need to know a lot about the internal anatomy and tissue structure of
the zebra mussels. As of right now, very little is known. Right now industrial plants try
to control the zebra mussels with equipment to preoxidize water at the point of intake, or
use chemical treatments, mechanical controls, or filtration. There is no single, ideal
solution.
DNA
The first DNA sequence data for dreissenid mussels has recently been obtained
from two mitochondrial regions, cytochrome b and ND4. Analysis of DNA substitutions
in these regions confirm species-level separation between the zebra and quagga mussels.
The North American zebra mussel is genetically diverse, suggesting that the population
was founded by relatively large numbers of divergent individuals. An extremely high
level of genetic divergence was found in the cytochrome b gene, suggesting that variation
within this species makes the zebra mussel one of the most genetically diverse known.
For example, two individuals from the same location share only 82.3% of the sequence
and are unique at 17.6% of the bases, suggesting a key factor in the mussels’ ability to
rapidly colonize new habitats and adapt to new environments.
Sea Grant Zebra Mussel Report/ Biology and Life History 13
7/1/93 to 6/30/95
There is high genetic variability among Great Lakes zebra mussels. A second
Dreissena species in the Great Lakes has been identified. There is a low level of genetic
differentiation among Great Lakes zebra mussel population. Average heterozygosity
among seven European populations examined was similar, indicating that little genetic
variation was lost when zebra mussels were transported to North America.
In order to obtain control over the spread of the mussels, DNR (Department of
Natural Resources) and other environmental agencies educate boaters and anglers how to
clean their equipment and what to watch for. Also it is against the law to purposely move
zebra mussels from one place to another, or even to just take them home. New sightings
should be reported to the DNR.
Bibliography:
www.greatlakes.net
http://www.twingroves.district96.k12.il.us/Wetlands/ZebraMussel/ZMHAbitat.html
DNR Department of Natural Resources, Michigan City, IN
.