| a field guide to aquatic exotic plants
and animals 
EXOTIC INTRODUCTIONS
"Exotic" species—organisms
introduced into habitats where they are not native—are severe world-wide agents
of habitat alteration and degradation. A major cause of biological diversity loss
throughout the world, they are considered "biological pollutants." Introducing
species accidentally or intentionally, from one habitat into another, is risky
business. Freed from predators, parasites, pathogens, and competitors that have
kept their numbers in check, species introduced into new habitats often overrun
their new home and crowd out native species. In the presence of enough food and
a favorable environment, their numbers will explode. Once established, exotics
rarely can be eliminated. Most species introductions are the work of humans.
Some introductions, such as carp and purple loosestrife, are intentional and do
unexpected damage. However, many exotic introductions are accidental. The species
are carried in on animals, vehicles, ships, commerical goods, produce, and even
clothing. Some exotic introductions are ecologically harmless and some are beneficial.
Other exotic introductions are harmful to recreation and ecosystems. They have
even caused the extinction of native species—especially those of confined
habitats such as islands and aquatic ecosystems. The recent development of
fast ocean freighters has greatly increased the risk of new exotics in the Great
Lakes region. Ships take on ballast water in Europe for stability during the ocean
crossing. This water is pumped out when the ships pick up their loads in Great
Lakes ports. Because the ships make the crossing so much faster now, and harbors
are often less polluted, more exotic species are likely to survive the journey
and thrive in the new waters. Many of the plants and animals described in
this guide arrived in the Great Lakes this way. They are now being spread throughout
the continent's interior in and on boats and other recreational watercraft and
equipment. This guide is designed to help water recreationalists recognize
these exotics and help stop their further spread.
MIDWEST AQUATIC EXOTICS
 Round
goby (Neogobius melanostomus) is a bottom-dwelling fish, native to
eastern Europe, that entered the eastern Great Lakes in ballast water. They can
spawn several times per year, grow to about 10 inches, are aggressive, and compete
with native bottom-dwellers like sculpins and log perch. They are expected to
be harmful to Great Lakes and inland fisheries.
 Sea
lamprey (Petromyzon marinus) are predaceous, eel-like fish native to
the coastal regions of both sides of the Atlantic Ocean. They entered the Great
Lakes through the Welland Canal about 1921. They contributed greatly to the decline
of whitefish and lake trout in the Great Lakes.  Rusty
crayfish (Orconectes rusticus) are native to streams in the Ohio, Kentucky,
and Tennessee region. Spread by anglers who use them as bait, rusty crayfish are
prolific and can severely reduce lake and stream vegetation, depriving native
fish and their prey of cover and food. They also reduce native crayfish populations.
 White
perch (Morone americana) are native to Atlantic coastal regions and
invaded the Great Lakes through the Erie and Welland canals. Prolific competitors
of native fish species, white perch are believed to have the potential to cause
declines of Great Lakes walleye populations.  Flowering
rush (Botumus umbellatus) is a perennial plant from Europe and Asia
that was introduced in the Midwest as an ornamental plant. It grows in shallow
areas of lakes as an emergent, and as a submersed form in water up to 10 feet
deep. Its dense stands crowd out native species like bulrush. The emergent form
has pink, umbellate-shaped flowers, and is 3 feet tall with triangular-shaped
stems.  Curly-leaf
pondweed (Potamogeton crispus) is an exotic plant that forms surface
mats that interfere with aquatic recreation. The plant usually drops to the lake
bottom by early July. Curly-leaf pondweed was the most severe nusiance aquatic
plant in the Midwest until Eurasian watermilfoil appeared. It was accidentally
introduced along with the common carp.
ZEBRA MUSSEL
Dreissena polymorpha
Zebra mussels and a related species,
the Quagga mussel, are small, fingernail-sized mussels native to the Caspian Sea
region of Asia. They were discovered in Lake St. Clair near Detroit in 1988. Tolerant
of a wide range of environmental conditions, zebra mussels have now spread to
parts of all the Great Lakes, the Mississippi River, and are showing up in inland
lakes. Zebra mussels clog water-intake systems of power plants and water treatment
facilities, as well as irrigation systems, and the cooling systems of boat engines.
They have severely reduced, and may eliminate native mussel species. Zebra
Mussel
Dreissena polymorpha
Many zebra mussles attached to a native clam.
Adult life size: 1/4 to 1 inch.
Female zebra mussels can produce as many as 1 million eggs per year. These
develop into microscopic, free-swimming larvae (called veligers) that quickly
begin to form shells. At about three weeks, the sand grain-sized larvae start
to settle and attach to any firm surface using "byssal threads". They will cover
rock, metal, rubber, wood, docks, boat hulls, native mussels, and even aquatic
plants. Zebra mussels filter plankton from the surrounding water. Each mussel
can filter about one quart of lake water per day. However, not all of what they
remove is eaten. What they don't eat is combined with mucus as "pseudofeces" and
discharged onto the lake bottom where it accumulates. This material may benefit
bottom feeders while reducing the plankton food chain for upper water species.
Diving ducks, the freshwater drum, and other fish eat zebra mussels, but will
not significantly control them. Likely means of spread:
Microscopic larvae
may be carried in livewells or bilge water. Adults can attach to boats or boating
equipment that sit in the water.
RUFFE
Gymnocephalus cernuus The ruffe is a small European member
of the perch family that is native to central and eastern Europe. It was introduced
to the Duluth harbor, probably in tanker ballast water, around 1985, and is spreading
to other rivers and bays around Lake Superior. In Europe, the ruffe is a pest
species in waters it has invaded. Ruffe have shown explosive population growth
and have had harmful impacts on native species and functions of aquatic ecosystems.
In the St. Louis River near Duluth, populations of yellow perch, emerald shiners,
and other forage fish caught in survey trawls, have declined dramatically as numbers
of ruffe have increased. The ruffe's ability to displace other species in
newly invaded areas is due to: - Its high reproductive rate,
- Its feeding
efficiency across a wide range of environmental conditions, and
- Characteristics
that may discourage would-be predators such as walleye and pike.
Ruffe
Gymnocephalus cernuus
Adult life size: 3 to 5 inches Ruffe grow rapidly and can reproduce
in their first year. In the St. Louis River, females can lay between 45,000 and
90,000 eggs a year. Ruffe are primarily bottom feeders, preferring dark environments
where they can hide from predators. Ruffe rarely grow bigger than 5 inches, although
the sharp spines on their gill covers, dorsal and anal fins make them difficult
for larger fish to eat. Likely means of spread:
Ruffe could be
accidentally transported in livewells, bilge water, bait buckets, and in the ballast
water of Great Lakes freighters.
SPINY WATERFLEA
Bythotrephes cederstroemi The spiny waterflea, or "B.C.",
is not an insect at all, but a tiny (less than half an inch long) crustacean with
a long, sharp, barbed tail spine. A native of Great Britain and northern Europe
east to the Caspian Sea, the animal was first found in Lake Huron in 1984—probably
imported in the ballast water of a transoceanic freighter. Since then, populations
have exploded and the animal can now be found throughout the Great Lakes and in
some inland lakes. Spiny WaterFlea
Bythotrephes cederstroemi
On
a line, spiny waterfleas look like bristly gobs of jelly with black spots.
Adult life size: 3/8 inch The effects spiny waterfleas will have on the ecosystems
of the Great Lakes region are unclear. The animals may compete directly with young
perch and other small fish for food, such as Daphnia zooplankton. They
also may provide a food sorce for larger fish. Spiny waterfleas also reproduce
rapidly. During warm summer conditions, each female can produce up to 10 offspring
every two weeks. As temperatures drop in the fall, eggs are produced that can
lie dormant all winter. While the impacts of the spiny waterflea seem to be
minimal in some areas of the Great Lakes, it is not known if this exotic will
have larger impacts on inland lake ecosystems.
Likely means of spread
Spiny waterflea eggs and adults may wind up unseen in bilge water, bait buckets,
and livewells. Also, fishing lines and downriggers will often be coated with both
eggs and adults.
EURASIAN WATERMILFOIL
Myriophyllum spicatum
Eurasian watermilfoil was accidentally
introduced to North America from Europe. Spread westward into inland lakes primarily
by boats and also by waterbirds, it reached midwestern states between the1950s
and 1980s. In nutrient-rich lakes, it can form thick underwater sands of tangled
stems and vast mats of vegetation at water's surface. In shallow areas, the plant
can interfere with water recreation such as boating, fishing, and swimming. The
plant's floating canopy can also crowd out important native water plants. A key
factor in the plant's success is its ability to reproduce through stem fragmentation
and underground runners. A single segment of stem and leaves can take root and
form a new colony. Fragments clinging to boats and trailers can spread the plant
from lake to lake. The mechanical clearing of weed beds for beaches, docks, and
landings creates thousands of new stem fragments. Removing native vegetation creates
perfect habitat for invading Eurasian watermilfoil. Eurasian Watermilfoil
Myriophyllum spicatum
Eurasian watermilfoil typically has 12 to 21 pairs of leaflets. The native
northern watermilfoil, with which it is often confused, usually has 5 to 9 pairs.
Left: Leaflet is 1/2 life size. Right: Mature plant. Eurasian watermilfoil
has difficulty becoming established in lakes with well established populations
of native plants. In some lakes, the plant appears to coexist with native flora
and has little impact on fish and other aquatic animals. Likely means of
spread
Milfoil may become entangled in boat propellers, or may attach
to keels and rudders of sailboats. Stems can become lodged among any watercraft
apparatus or sports equipment that moves through the water, especially boat trailers.
PURPLE LOOSESTRIFE
Lythrum salicaria
Purple loosestrife is a wetland plant from Europe and Asia. It was introduced
into the east coast of North America in the 1880s. First spreading along roads,
canals, and drainage ditches, then later distributed as an ornamental, this exotic
plant is in 40 states and all Canadian border provinces. Purple loosestrife
invades marshes and lakeshores, replacing cattails and other wetland plants. The
plant can form dense, impenetrable stands which are unsuitable as cover, food,
or nesting sites for a wide range of native wetland animals including ducks, geese,
rails, bitterns, muskrats, frogs, toads, and turtles. Many rare and endangered
wetland plants and animals are also at risk. Purple Loosestrife
Lythrum
salicaria
Adult height: 2 to 7 feet. Purple loosestrife thrives on disturbed, moist
soils, often invading after some type of construction activity. Eradicating an
established stand is difficult because of an enormous number of seeds in the soil.
One adult plant can disperse 2 million seeds annually. The plant is able to resprout
from roots and broken stems that fall to the ground or into the water. A major
reason for purple loosestrife's expansion is a lack of effective predators in
North America. Several European insects that only attack purple loosestrife are
being tested as a possible long-term biological control of purple loosestrife
in North America. Likely means of spread
Seeds escape from gardens
and nurseries into wetlands, lakes, and rivers. Once in aquatic systems, seeds
are easily spread by moving water and wetland animals.
CHECKLIST
Clean boats, clean waters...
If you are a water recreationalist —
boater, angler, water-skier, scuba-diver, sailor, or canoeist — there are
some important things you can do to prevent the transport of harmful exotic species
from one lake or river to another. In some states and provinces it is illegal
to transport harmful exotic species. - Inspect your boat, trailer,
and boating equipment (anchors, centerboards, rollers, axles) and remove any plants
and animals that are visible before leaving any waterbody.
- Drain
water from the motor, livewell, blige, and transom wells while on land before
leaving any waterbody.
- Empty your bait bucket on land before
leaving the waterbody. Never release live bait into a waterbody, or release aquatic
animals from one waterbody into another.
- Wash and dry your boat, tackle,
downriggers, trailer, and other boating equipment to kill harmful species that
were not visible at the boat launch. This can be done on your way home or once
you have returned home. Some aquatic nuisance species can survive more than 2
weeks out of the water, so it is important to:
- rinse your
boat and equipment that normally get wet with (at least 40°C
or 104°F) tap water; or
- spray your boat and trailer with high-pressure
water; or
- dry your boat and equipment for at least 5 days, before transporting
to another waterbody.
- Learn what these organisms look like (at
least those you can see). If you suspect a new infestation of an exotic plant
or animal, report it to your natural resource agency.
- Consult your
natural resource agency for recommendations and permits before you try to control
or eradicate an exotic "pest." Remember, exotic "pest" species thrive on disturbance.
Do-it-yourself control treatments often make matters worse and can harm native
species.
INFORMATION The information
on this Web page was originally produced in brochure form by the Minnesota Department
of Natural Resources copyright 1995 with support and cooperation of Minnesota
Sea Grant, The U.S. Fish and Wildlife Service, and the U.S. Army Corps of Engineers.
If you would like more information about exotic species, the problems they
cause, regulations to prevent their spread, or methods and permits for their control,
contact one of the following offices:
| |
Minnesota-DNR
Purple Loosestrife Program
500 Lafayette Road
St. Paul, MN 55155-4025
612.259.5100 | | |
University of Minnesota
Minnesota Sea Grant Program
Exotic
Species Info Center
2305 East 5th Street
Duluth, MN 55812-1445
218.726.8712
| If you would like information about booking a traveling
exhibit or educational trunk on aquatic exotic species, contact: The Bell
Museum of Natural History
10 Church St. SE
University of Minnesota
Minneapolis, MN 55455
612.624.2090 | 
