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Water for Our Future
IISG-98-10 Exotic
Species
L. E. Dorworth, Department of
Biological Sciences, Purdue University Calumet, Hammond, Indiana
Since the 1800's, at least 139
nonindigenous aquatic organisms have become established in the Great
Lakes including species of plants, fish, algae, mollusks, and
oligochaetes. The impacts caused by species, such as the
sea
lamprey (Petromyzon marinus),
zebra
mussel (Dreissena polymorpha),
purple
loosestrife (Lythrium salicaria),
Eurasian
watermilfoil (Myriophyllum spicatum), and
spiny water
flea (Bythotrephes cederstroemi) have not only taken their
toll in the Great Lakes but are also spreading to inland waters.
Section 1203 of the Nonindigenous Aquatic Nuisance Prevention and
Control Act of 1990 (Public Law 101-646) provides guidance for
the development of state plans and authorizes federal cost share support
by the national Aquatic Nuisance
Species (ANS) Task Force. The Task Force has worked since
1991 to prevent, control, and manage the occurrence of aquatic nuisance
species in the Great Lakes.
How Do They Get To Our
Waters?
A number of these organisms are getting a free
ride in ballast water of large ships. The ballast of a large ship is
filled and emptied when necessary to provide stability and has become a
pipeline for the transport of nonindigenous species around the world. A
series of invasions of exotics into U.S. waters has occurred. The animal
to catch the attention and imagination of the American public within the
past ten years is the zebra mussel. Instead of costing a few thousand
dollars to control, it has cost millions and still is not under control.
The barnacle sized mussel attaches to most hard substrates. Power
companies, water treatment facilities and other water dependent
industries have had a continuous battle in clearing intake pipes and
keeping screens clean of the thick mats of the mussels.
As authorities struggle to keep exotics species
such as the zebra mussel under control, other species are being
intentionally released into waters to control other "nuisance" species.
Organisms being managed through control range from plants to animals,
whereas others are just being released to create a sports fishing
industry. One example of the release of an exotic to control an exotic
is the Asian grass carp. The carp is used in many states to control
aquatic weed growth (Table 1).
Common Names
Duckweed
Pondweed
Milfoil
Coontail
Waterweed
Muskgrass |
Scientific
Names
Lemna, Wolffia
Potemogeton, Najas
Myriophyllum
Ceratophyllum
Elodea
Chara |
Table 1. A few of the common
aquatic plants eaten by grass carp.
In Lake Michigan, the
zebra
mussel
is thought to have changed the
ecosystem and
the change is still in flux. Due to their ability to filter water, the
depth to which light penetrates is deeper, thereby allowing more benthic
algae to grow. The increase in certain aquatic plant communities, such
as the filamentous green algae and the loss of other communities, the
benthic algal community, results in a decline of certain desirable fish
species and other benthic organisms and an increase in other organisms
that may or may not be desirable. However, too many aquatic plants or
excessive plant growth can be considered a nuisance and may eventually
lead to a eutrophic water system. It is hypothesized that the zebra
mussel activities have indirectly enhanced the
benthic
invertebrate communities in the lake which results in increased
populations of bottom dwelling fish populations.
What to do to stop a possible
infestation?
Monitoring for zebra mussel populations is the
best way to determine if they are in your lake. Just because your lake
does not have a direct connection to another lake does not mean that
zebra mussels or any exotic organism can not be transported into your
lake. Movement of exotics between water bodies is usually done
unknowingly by a
boat
operator. For example, adult mussels and the veligers (larval stage
which is microscopic) can be transported on the hull of the boat, on the
boat's engine, in the ballast water and even on the aquatic weeds that
are caught on the trailer. Therefore, after a boat is removed from the
lake, the boat operator should inspect the hull as well as the trailer
and remove any attached animals or plants before leaving that particular
body of water. The boat operator would definitely want to flush the
boat's engine since zebra mussels, more specifically the veliger form
can get into the cooling engine and eventually clog the intake pipes.
Therefore, drain the water from the motor, livewell, bilge, and transom
wells while on land before leaving the waterbody area. Empty the bail
bucket on land, do not release aquatic organisms into a water body.
Also, has a final check to make sure the water craft is clean of
exotics, wash and dry the boat, tackle, downriggers, trailer and other
boating equipment. The recommended water temperature for rinsing
equipment is 104°F or 40°C tap water. The main reason for such a high
temperature is that certain exotics are capable of surviving outside an
aquatic environment for more than two weeks. If water at this
temperature is not available then spray the boat and trailer with high
pressure water or make sure the boat has been dry for at least five days
before transporting to another body of water If you find them on your
water craft report them to the
Department of Natural
Resources as well as remove them so that you don't transport them to
the next body of water. Besides checking for zebra mussels, the boat
operator should also check for plant fragments.
Hydrilla,
an aquatic nuisance species
can be transported from water body to water body by unknowing boat
operators as well.
More Detailed Information
Exotic species in the Great Lakes has been
reported extensively in various publications from many organizations
around the Great Lakes. Extensive information on zebra mussels and other
aquatic nuisance species is found on the
Sea
Grant Nonindigenous Species Web Site. The information on this web
site was pulled together by the
Great Lakes Sea Grant
Network and it was a project of the
National Sea Grant College
Program. Information contained on the site is current information
relevant to zebra mussels and other nonindigenous species from Sea Grant
publications and other research publications. Also see the list of
attached references for more information pertaining to this subject.
Recommended Resources
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