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Green Crab (Carcinus maenas)
DESCRIPTION
The European Green Crab (Carcinus maenas) is a small shore crab. Its native distribution is the Atlantic coasts of
Europe and Northern Africa, from Norway and the British isles south to Mauritania. They are generally found in areas
with protected rocky shores and cobbles to sand flats and tidal marshes. They can thrive in wide ranges of both
salinities and temperature.
Despite its name, the green crab is usually not green in color. Its shell is mottled and varies in color. During the
molting cycle, the green crab's color may change from green to orange, then red. The abdomen has five spines on
either side, and contains yellow patches. Their pair of hind walking legs are relatively flat. Their maximum size ranges
from 80 mm (3") to 65 mm (2.5").
The green crab is an able forager. Studies have shown that the green crab is capable of learning and improving upon
its food gathering skills. This ability has proven the green crab to be much quicker and more dexterous than most
other crabs. This leads to the crab's remarkable ability to open bivalve shells in more ways than others.
Green crabs feed upon numerous types of organisms including clams, oysters, mussels, marine worms, and small
crustaceans. They also will prey on juvenile crabs and shellfish.
The recent arrival of the green crab on the U.S. West Coast is cause for concern. The green crab has already invaded
numerous coastal communities outside of its native range, including South Africa, Australia, and both coasts of North
America. An able colonizer and efficient predator, this small shore crab has the potential to significantly alter any
ecosystem it invades. It has been blamed for the collapse of the soft-shell clam industry in Maine.
First seen in San Francisco Bay in 1989, the green crab has been moving northward to Humboldt Bay, California. Live
specimens have been found recently in Coos Bay, Oregon and Willapa Bay in Washington State.
IMPACTS
Voracious predator
The green crab feeds on many types of organisms, particularly bivalve mollusks (e.g., clams, oysters, and mussels),
polychaetes, and small crustaceans. For example, Since it can also prey on juvenile crabs and shellfish, a northward
spread to the Washington coast and Puget Sound could put our Dungeness crab, clam, and oyster fisheries at risk,
and the green crab may compete with native fish and bird species for food. In Bodega Bay, California, a significant
reduction in population abundance of clam and native shore crab is already evident since the arrival of the green crab
in 1993. In addition, the green crab is an intermediate host to a marine worm that can harm the health of local shore
birds.
Feeding habits and tolerance of a wide variety of environmental conditions
The feeding activity of green crab greatly impacts populations of mussels (Mytilus edulis), dogwhelks (Nucella lapillus),
and cockles (Cerastoderma edule). In Scotland, the crab acts as an intermediate host of the acanthocephalan worm,
Profilicollis botulus, which causes heavy mortalities in eider ducks (Somateria mollissima). Along the east coast of
North America, green crab preys on quahogs (Mercenaria mercenaria) and has been implicated in the demise of the
Atlantic soft-shell clam fisheries of the 1950's. In Bodega Harbor, California, a comparison of long-term (> 10 years)
sampling records shows a significant reduction in clam (Transennella spp.) and native shore crab (Hemigrapsus
oregonensis) population abundance since the arrival of green crab in 1993. Furthermore, laboratory studies show that
green crab readily preys on Dungeness crab (Cancer magister) of equal or smaller size. Dungeness crab spend part of
their juvenile life in the intertidal zone, and may therefore be at risk from green crab predation.
It is unknown how the crab established itself on the U.S. west coast. Potential pathways for introducing C. maenas to
Washington include, but are not limited to, the natural dispersal of larvae from an established population to the south,
discharge of ballast water from transoceanic ships, discard of seaweed packing materials used in shipping live
shellfish, and the interstate transport of shellfish aquaculture products and equipment.
ORIGIN
The Atlantic coasts of Europe and northern Africa, from Norway and the British Isles south to Mauritania. Occupies
protected rocky shores and cobbles to sandflats and tidal marshes. Lives in a wide range of salinities (5-30 ppt) and
temperatures (5-30 C).
Because of its feeding habits and tolerance of a wide variety of environmental conditions, green crab has invaded
numerous coastal communities outside its native range, including South Africa, Australia, and both coasts of North
America. The crab was introduced to the western Atlantic coast during the early 19 th century where it occurred
between New Jersey and Cape Cod. By the 1960's, it had spread north through Nova Scotia. In 1989-1990, green
crab was discovered in San Francisco Bay, California, although anecdotal reports place the crab in that state as far
back as the mid-1970's. Since its discovery in San Francisco Bay, green crab has been found as far north as Humboldt
Bay, California (summer 1995), and most recently, Coos Bay, Oregon (spring 1997).
CONTROL METHODS
The green crab has made its way to the coast of Washington State. Because of this the Washington Department of
Fish and Wildlife (WDFW) have taken some measures to try and stop the crab populations from spreading from
Willapa Bay to Puget Sound. The measures they have taken are:
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Coastal monitoring for presence of the crab
Enacting an emergency rule making the green crab a harmful exotic species and prohibiting the possession
and transportation of any live green crabs
Enacting an emergency regulation that prohibits transfer of any shell, shellfish or associated equipment and
vehicles from Willapa bay to any other Washington waters except with written authorization from WDFW
Canceling existing transfer permits and attaching strict conditions to new permits
Another type of control that is being used is the development of a management program used to track the spread of
the green crab. The management program includes these guidelines:
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No live aquatic plants and animals can be released into, or come in contact with the Puget Sound, without
written permission from the director of the WDFW
Transfer permits are required for shellfish growers on the coast to move products to portions of the state from
Willapa Bay
Ship operators should exchange ballast water outside Puget Sound to avoid introducing the crab
Seafood handlers, commercial shellfish growers and boat operators should thoroughly check their equipment
for the presence of green crabs before moving to crab-free waters
Just as there are management type controls there are also some biological control proposals for the green crab.
Biologists and scientists have suggested introducing some parasites as control. One parasite, Sacculina carcini,
apparently inhibits the molting of the crab, suppresses the development of male crabs, and causes sterilization in
female crabs.
Scientists and biologists think that this parasite could impact the reproductive output of the green crab ultimately
reducing the crabs abundance in the wild, but before they could use this parasite, its impact on native ecosystems
would have to be carefully considered because it is a non indigenous species. )
http://www.iisgcp.org/EXOTICSP/ans.htm#animals
Veined Rapa Whelk
(Rapana venosa)
Rapa whelk: The foreign sea snail, accidentally introduced into the Chesapeake Bay, devours
oysters and clams. The Bay, like other major estuaries, is a prime breeding ground for
invasive species brought to this country from abroad in ballast water.
DESCRIPTION
The Veined Rapa Whelk (Rapana venosa) is a member of the Muricidae, a family of predatory
marine snails. They eat a variety of mollusks and they often attack bivalves (oysters, clams,
mussels). Whelks may get to their prey by boring a hole into the edge of its shell or in the case
of bivalves, by rasping around the region where the two valves meet and prying it open. They
reproduce by laying egg clusters. Pelagic larvae hatch out of the eggs and sink to the bottom.
Then they develop a hard shell. The Veined Rapa Whelk has a heavy short spired shell with a
large inflated body whorl. The outer color is variable from gray to red brown, with dark brown dashes on the spiral ribs.
Most specimens have distinctive black veins throughout the shell. A very characteristic feature of the species is the
deep orange color found on the inside of the shell. Rapa whelks may grow to be quite large. The largest record in the
literature for the native range is 18.3 cm shell length from Taiwan. A length of 12.1 cm has been published from the
Black Sea. Several specimens in excess of 15 cm shell length have been collected from Hampton Roads, Virginia.
They prefer sandy bottoms where they can burrow. The Rapa Whelk is very versatile. It will tolerate low salinities,
polluted waters and oxygen deficient waters.
IMPACTS
Veined Rapa Whelks have caused changes in populations of bottom dwelling organisms, and have become marine
pests in the Black Sea. Research is still being conducted to determine the impacts of these whelks on native species
and their ecosystems.
ORIGIN
Rapa whelks are native to the Sea of Japan. The Veined Rapa Whelk is restricted to the Yellow Sea, the East China
Sea and the Bohai Sea. This is a region of wide annual temperature ranges, comparable to that of the Chesapeake
Bay. In winter populations may migrate from estuarine waters into deeper water (possibly to avoid freezing surface
water). This species was introduced into the Black Sea in the 1940s, and later spread to the Aegean and Adriatic
seas. Now Rapa Whelks are also located in the Chesapeake Bay area. Scientists believe whelk larvae were
transported to different locations in ship ballast water.
CONTROL METHODS
Currently as a form of control, there is a bounty being paid for Rapa
Whelks in the United Sates. A bounty of $5 per snail will be paid for LIVE
Rapa Whelks. A bounty of $2 per snail will be paid for DEAD Rapa Whelks
or empty Rapa Whelk shells.
DISTRIBUTION
Veined rapa whelks: Current distribution in Chesapeake Bay
The map to the left shows the known distribution of veined rapa whelks in
the Chesapeake Bay, USA as of February 1, 2006. The bulk (99%) of the
more than 11, 000 individual whelks collected since September 1998 are
from the yellow area. A single rapa whelk was collected near Tangier Light
early in 2005 (Harding and Mann 2005) making Tangier Light the
northernmost collection point for whelks in Chesapeake Bay.
Common Reed
(Phragmites australis)
DESCRIPTION
Common reed is a tall, native, warm-season, perennial, sod-forming grass.
These non-native plants have spread throughout Virginia wetlands –
including in Back Bay – displacing native species that animals have used
as food sources. The species, while large and “showy,” do not provide the
same food value to the animals in the area.
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Field Marks: This grass is distinguished by its huge stature, up to 12 feet tall, and its large panicle of
spikelets.
Habitat: Along streams, around ponds, sloughs, reclaimed stripmine areas.
Stems: Erect, smooth, up to 12 feet tall.
Leaves: Flat, elongated, smooth, up to 2 1/2 inches broad.
Flowers: 3-7 flowers per spikelet, with many spikelets arranged in a large, dense, much-branched panicle up
to 1 1/4 feet long; spikelets 3/4 inch long, bearing numerous silky hairs.
IMPACTS
Common reed can be considered a natural component of some undisturbed wetlands. However, the invasive strain
grows aggressively in areas that are disturbed or stressed by pollution, dredging or other alteration of the natural
hydrologic regime. Invasive stands of common reed grass eliminate diverse wetland plant communities, providing little
food or shelter for wildlife.
On the contrary, common reed is considered in many areas as a valuable economic entity. It can be used in building
houses by creating a thatched roof. It is often used as a craft material for projects such as weaving mats or baskets as
well as rope-making. It has been used medicinally as a diuretic and as a source of cellulose. It can also be used for
food for humans, cattle, and horses.
ORIGIN
Common reed is a native American species. Research is being conducted to determine if a non-native aggressive
strain was carried to North America in the early 20th century. The native species may have found a new niche in
human-disturbed habitat. It can now be found throughout the United States.
CONTROL METHODS
There seems to be no good way to control the species once it has invaded an area. There are some ways that work
better than others. One variable that is definitely needed is time. A long-term management plan is required to fully
eradicate the species from an area. Since the plant spreads through rhizomes, it is difficult to get rid of it entirely. One
of the better methods to follow is to combine the use of mechanical and chemical control. The best control is
prevention and the best way to prevent the species from invading is to minimize disturbances of the land as well as
minimizing water pollution.
Mechanical/Physical Control
Cutting, pulling or moving can be done in late July and should be repeated for several years. All cut shoots should be
carefully removed to prevent re-sprouting. The placement of black plastic over cut stems has had some success and
burning in combination with herbicide application has also been effective in some situations. Hydrologic controls such
as flooding for an extended period during the growing season may also be successful.
Chemical Control
Herbicide application with Accord, Rodeo or Glypro is most effective in the early fall, after tasseling, and should be
applied at least two years in a row. Fusilade DX, a grass specific herbicide can be applied in non-aquatic areas.
Methods of application will depend on the associated plant community but may include aerial spraying, hand-held or
backpack sprayers and hand-wicking.
York River experiment finds Japanese oysters resist diseases
About Oyster Diseases
Since the early 1980s, diseases have overwhelmed oyster populations in the Chesapeake Bay, causing losses of up to
90 percent of stocks in some areas. These heavy mortalities have been linked to the spread and intensification of two
parasites: Dermo (Perkinsus marinus) and MSX (Haplosporidium nelsoni). Though deadly to the oysters, neither
affects humans, whether the oysters are eaten raw or cooked.
Dermo is a disease caused by a single-celled organism (protozoan) that infects oysters, eventually reaching such high
numbers within the oyster host that the oyster can no longer maintain its physiological functions, and dies. The exact
mechanisms by which the parasite kills the host are not understood. Dermo tends to have its largest impact on oysters
about the time they reach market size.
MSX disease is also caused by a protozoan. It is more virulent than Dermo, although as far as is known, it also kills by
reproducing to vast numbers within oyster tissues and overcoming the oyster’s ability to maintain its functions. MSX
does more damage to young, or small, oysters than Dermo.
By Karl Blankenship
Japanese oysters appear to be resistant to the two oyster diseases that have devastated native oyster populations in
the Chesapeake Bay — a finding that may boost efforts to find a disease-resistant gene that could aid the native
species. The finding came from a controversial experiment that began June 29 when trays containing 200 Japanese
oysters and 400 Bay oysters were placed in the York River. Since then, researchers from the Virginia Institute of
Marine Sciences found that 95 percent of the native eastern oyster, Crassostrea virginica, died from the diseases MSX
and Dermo. None of the Japanese oysters, Crassostrea gigas, died as the result of disease.
Eugene Burreson, an oyster disease specialist at VIMS, said the field study confirmed earlier laboratory work
indicating that although the Japanese oyster could be infected by Dermo, the number of parasites remained low and
did not prove fatal as in native oysters. Dermo infected about 25 percent of the Japanese oysters, he said. “The more
important news is that the gigas did not get MSX at all,” Burreson said. “And we had a very heavy challenge — there
was lots of MSX in the water.” Burreson said the finding was somewhat of a surprise to researchers. “We thought
there would be a low level of infection, but there wasn’t,” he said. “We didn’t see any MSX in the gigas at all.” The
latter finding was particularly significant because, unlike Dermo, scientists have been unable to conduct studies with
MSX in the laboratory.
About 20 percent of the Japanese oysters died during the summer and fall, but not as the result of disease, Burreson
said. The reason for their death is uncertain, but Burreson speculated it may have stemmed from the use of a needle
to withdraw a blood sample from each Japanese oyster before being used in the experiment. “They had a wound,
essentially, and it may be partially related to that,” Burreson said. Whatever the cause, Burreson said the 20 percent
mortality rate was not alarmingly high.
Although the Japanese oyster proved disease resistant, it did not grow well in the York River during the summer,
Burreson said, though growth appeared to increase in the fall as temperatures cooled. “It may be just as simple as it’s
very hot here in the summer and they’re not used to those sorts of conditions,” Burreson said. “Salinity can get quite
low here as well, and they’re mainly a cool-water, high-salinity organism. We just don’t know what they’re going to do
in these conditions.”
The study is scheduled to end after a year, and scientists hope to learn more about the Japanese oyster’s growth as
the experiment continues through the winter and spring. “I think we’ve probably learned what we wanted to learn
about their disease susceptibility,” Burreson added, “but we haven’t learned all that we want to learn about their growth
and survival.”
The York River study was prompted by scientists who were curious whether the Japanese oyster, which has proved to
be more disease resistant elsewhere, would fend off the parasites that have caused Bay oyster harvests to fall more
than 90 percent in the past two decades. The proposal was strongly opposed by the state of Maryland, environmental
groups, and others who feared the experiment would lead to an introduction of the foreign oyster. Such an introduction,
they argued, could eventually eliminate the native species from the Bay and pose unforeseen ecological
consequences to the Chesapeake.
Most of the opposition subsided after researchers promised that all oysters used in the experiment would be certified
as being triploid. Triploid oysters have been chemically treated to produce three sets of genes instead of two. Triploid
oysters typically cannot reproduce and, if they do, the young cannot survive beyond larval stages. Each oyster used in
the experiment had a blood sample taken to make sure the treatment worked.
Proponents of the experiment have said that if the Japanese oyster could survive in the Bay, it could lead to efforts to
identify a gene or combination of genes in the foreign species that might be used to make the native species resistant
as well. “That’s a long ways off, of course,” Burreson said. “It involves a lot of genetic research.” VIMS, the state of
Maryland, and environmental groups are strongly opposed to any outright introduction of reproducing Japanese oyster
stocks in the Bay.
Source: Maryland Department of Natural Resources
Snakehead Fish (Channa argus)
Snakehead fish: This Asian predator could seriously harm other species in the Potomac River watershed, where many
have been found. The northern snakehead can grow to 3 feet long, has canine like teeth and a long dorsal fin, and can
leave water and “walk” on its pectoral fins to reach new waterways.
DESCRIPTION
This fish is considered a predator for the large amounts of food it can devour. If it were large enough, it could even eat
a human!
Usually snakehead fish have a brown to greenish color. They have several diagonal bands that are dark and form
angles or rectangular spots that are often accompanied by rows of spots that appear to be mother of pearl in color. In
most cases, the dorsal and anal fins seem to be red.
All snakeheads are distinguished by their torpedo shaped body, long dorsal and anal fins without spines, and sharply
toothed jaws. This snakehead typically has red eyes and is gold-tinted brown to pale gray in younger fish while older
fish are generally dark brown with large black blotches. The most distinctive marking is the black spot rimmed with
orange near the base of the tail fin, known as an eye-spot.
The snakehead (also once called the "serpent headed fish") has inspired various other beliefs and myths through the
centuries. Because of its serpent-like head, some oriental cultures believed the snakehead had a poisonous bite (but
that is not true). A western scientist studying these species in 1878 wrote how the Karen people of Burma regarded
this fish with "superstitious awe" and refrained from eating them. Another source stated in 1822 that the religious
people of Bengal Province in India believed it was unlucky to regard the snakehead as either bad or good.
Snakehead fish can be quite large, with the typical adult ranging in size between 2.5 and 5 feet, and can produce
anywhere from 1,300 to 15,000 eggs per spawn multiple times a year (USGS). Their typical diet consists mostly of
other fishes along with crustaceans, frogs, and small reptiles. As unbelievable as it sounds, the fish has even been
known to eat small birds and mammals. The snakehead's varied and voracious appetite poses a major threat to both
the smaller fish it encounters, as well as to the other fish that compete with it for food.
Despite the common myth, the snakehead cannot literally walk on dry land, but it is capable of living for several days
out of water as long as it is in a moist environment. The fish may leave a body of water with low oxygen levels to
"wallow" on land into another body of water. This unique ability, as well as its imposing size and appetite, place the
snakehead among the top predatory fish in its new habitat, and give it the potential to quickly overwhelm native
species.
DIET
As juveniles, they seek zooplankton, insect larvae, small crustaceans and the fry, or young, of other fishes. As adults
(they can grow to nearly 5 feet and weigh as much as 13.5 pounds), they feed on other fishes, larger crustaceans,
frogs, small reptiles and, sometimes, birds and mammals.
IMPACTS
The northern snakehead, has the potential to expand its range throughout most of the United States and into Canada,
Orrell says. Proliferation of the snakehead in the United States is cause for alarm for several reasons. One is that
these voracious eaters compete with native species for food. Other threats are their ability to live out of water for up to
three days—the snakehead can breath oxygen in the air—and their tendency to “walk” over land by wriggling. Both
abilities allow them to disperse widely.
“The northern snakehead presents a formidable environmental threat that has the potential to upset the natural
balance of freshwater ecosystems in the United States,” Orrell says.
ORIGIN
One of the newest "foreign invaders" in the United States is the northern snakehead fish (Channa argus). The
northern snakehead was first reported in the United States in 1977, when it was found in Silverwood Lake, California.
Since that time, the invasive species has been discovered in bodies of water in states as different in temperature and
geography as Maryland, North Carolina, Florida, and Wisconsin. The snakehead was brought to the U.S. as a food
source -- the fish is considered a delicacy and reportedly, an aphrodisiac, in its native lands -- but, no one knows why
the fish were released into local rivers and ponds. Unfortunately, once released, the snakehead has proven difficult to
control.
CONTROL METHODS
Despite the snakehead's slow spread across state lines, once the fish is found in a local body of water, it has proven
difficult to eradicate. In places such as the Potomac River, scientists have been taken aback by the burgeoning
population of snakehead fish found only a few years after introduction. States have implemented a variety of methods
in an attempt to control the invasive species. In several ponds, the chemical Rotenone was applied; the application
usually did kill the snakehead, but unfortunately, also most other fish in the pond. For rivers, control methods have
been confined to catch and report. Some states have even offered a bounty for snakehead fish. However, due to
fishermen's reports of migrating and thriving populations of the invasive species, many states are currently reevaluating their monitoring and control policies.
Troublesome Chinese mitten crabs infiltrate Chesapeake Bay
The mitten crab is identifiable by the hairs on its claws. A delicacy
in China, the crabs are a problem here. BRITISH MARINE LIFE STUDY SOCIETY
By SCOTT HARPER , The Virginian-Pilot
© June 5, 2007
It has hairy claws and should not be here. But the Chinese mitten crab - a large, spidery creature classified by the
U.S. government as "injurious wildlife" - keeps popping up in the Chesapeake Bay and, more recently, in the Delaware
Bay.
While none of the foreign species have been confirmed in Virginia waters - the closest one was found in the Bay in
southern Maryland - scientists on Friday issued an alert to biologists, fishermen and wildlife managers on the East
Coast to be on the lookout for the nuisance crab.
A Chinese mitten crab hot line has been set up. So too has a Chinese mitten crab survey, as well as a Chinese mitten
crab monitoring team. Why all the fuss? While the crabs are coveted by seafood lovers in their native China - the
eggs are considered aphrodisiacs - these spindly-legged, brownish-colored crustaceans are mostly a pest in other
nations where they have spread.
Mitten crabs can swarm over riverbanks, cause erosion by burrowing into muddy banks, and tear up fishing nets. In
the Chesapeake Bay, experts worry that the invaders might compete with and damage populations of native blue
crabs, which already are stressed by pollution, lost habitat and fishing pressures. Scientists now believe that Chinese
crabs may be reproducing in the Bay and could already have a foothold in the ecosystem. "Some recent analyses
suggest that the Chesapeake Bay provides very suitable environmental conditions for colonization and that the crab
could spread to other estuaries as well," wrote Greg Ruiz, a senior scientist at the Smithsonian Environmental
Research Center in Edgewater, Md.
Ruiz and other Maryland scientists have been closely monitoring mitten crabs since the first one was caught two years
ago by a commercial fisherman in the Patapsco River, near Baltimore Harbor. Another one was snagged a few days
later, also in a crab trap on the Patapsco, and then another last month off Chesapeake Beach in southern Maryland.
Also last month, the first Chinese crab was confirmed in Delaware Bay, raising concerns that the species may already
be migrating to a neighboring estuary.
Ruiz and others suspect that the crabs arrived on the East Coast in the ballast water of foreign ships. But because
they are a popular seafood among Asian consumers, there is a chance they were illegally trafficked here, the scientists
said. So far, Chinese crabs have invaded San Francisco Bay in California, as well as rivers and estuaries in Germany
and England. Once in these new waters, their numbers boomed, according to researchers.
Unlike blue crabs, Chinese crabs live in freshwater rivers but reproduce in salty estuaries. Also unlike blue crabs, they
do not swim, but instead walk on eight sharp-tipped legs.
Rob O'Reilly, assistant director of fisheries at the Virginia Marine Resources Commission, said the state is keeping a
watchful eye. "Certainly it's something to be concerned about," O'Reilly said. Roger Mann, a shellfish expert and
research biologist at the Virginia Institute of Marine Science, said he is not sure Chinese crabs would do well in state
waters, noting the temperatures may be too high in summer. "I frankly would not expect to see a lot of them down
here," Mann said.
In recent years, Virginia officials have confirmed two other new invasive species in the southern half of the
Chesapeake Bay - the snakehead, an aggressive and toothy fish found mostly in the Potomac River, and the veined
rapa whelk, a baseball-size snail thought to relish clams and oysters.
 Reach Scott Harper at (757) 446-2340 or [email protected].
Zebra mussel (Dreissena polymorpha)
Background
Zebra mussel (Dreissena polymorpha) is a temperate freshwater bivalve species
native to the Black and Caspian seas of Russia and the Ukraine. The mussels made
their way to Western Europe through canals and inland waterways that were used for
trade during the Industrial Revolution. Zebra mussels first arrived in the United States
around 1985, when transoceanic ships released ballast water into Lake St. Clair of the
Great Lakes. The ballast water, which is taken into a ship's hold so that it can maintain
its weight after it has unloaded its cargo, likely contained veligers and adult zebra
mussels.
Adult zebra mussels measure between 0.5 and 3.5 cm in length. The mussels' shells are characterized by dark brownand-cream concentric banding, which gives the animal its "zebra"-like appearance. Like many successful invasive
species, the zebra mussel is prolific. Females can release 30,000 to one million eggs per year. Spawning can begin in
May and last until October. Adult mussels eventually generate a tuft of fibers called a byssus, which will attach to most
any surface such as rock, fiberglass, rubber, vinyl, wood, metal or glass. Concentrated beds of mussels can contain up
to 100,000 mussels per square meter. Additionally colonization can occur at varying depths.
The Problem
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The colonization patterns of zebra mussels damage water intake structures such as power and municipal
water treatment plants. It is estimated that the zebra mussel has cost the power industry $3.1 billion since
1993.
Attachment to boat motors, docks, buoys and pipes have affected recreation industries.
Recreational beaches that become littered with the shells also are affected; the sharp-edged shells can harm
bare feet.
Zebra mussels are hearty filter-feeders that can significantly reduce the supply of microscopic zooplankton,
which many forage fish depend upon.
Zebra mussel control is costly!
The Solution
Due to the high cost of coping with the impact of zebra mussels, the spread of zebra mussels is a very serious matter.
Due to their potential threat and damage, the Chesapeake Bay Program designated the zebra mussel as a high priority
species and Program partners are developing a plan to prevent their spread.
Although zebra mussel populations are not widespread in the Bay watershed, several isolated populations have been
discovered. Small populations of zebra mussels have been found in quarries in Virginia and Pennsylvania as well as a
lake in New York that has an outlet stream to the Susquehanna River. Resource managers are currently working to
eradicate the zebra mussel populations from these locations to prevent further spread.
With proper attention and education, the spread of zebra mussels can be stopped. Boat owners and SCUBA divers
must be sure to thoroughly clean their boats and equipment before leaving a waterway that may contain zebra
mussels.
How YOU Can Help:
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Remove any visible mud, plants, fish or animals before transporting equipment.
Drain at the site of origin bilges, live wells and any other compartments that could hold water.
Clean and scrub boat hulls, anchors and trailer. Hose equipment with hot and/or high pressure water.
Clean and dry anything that came in contact with water (Boats, trailers, equipment, clothing, dogs, etc.)
Never release plants, fish or animals into a body of water unless they came out of that body of water.
As an added precaution, allow all equipment (dive gear, boats, etc.) to dry thoroughly before using it again at
another site; five days if possible.
Invasive Species in the Chesapeake Bay
Directions: Using the information on the following pages, answer these questions ON YOUR OWN
PAPER.
Green Crab
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7.
Where is the green crab native to?
What colors, besides green, can the green crab be?
What do green crabs eat?
What problem has the green crab caused in Maine?
What 3 types of fisheries could be severely at risk because of the green crab?
When and where was the green crab first introduced to western Atlantic coast?
What can the non-native species of the Sacculina carcini parasite do to control the spread
of the green crab?
8. What do you think of the idea of introducing this parasite into the ecosystem?
Veined Rapa Whelk
9. What does the rapa whelk like to eat?
10. How do rapa whelks open bivalves?
11. What is the size of the largest rapa whelk found in Hampton Roads?
12. Where are the Veined rapa Whelks native to?
13. How is it believed that the rapa whelks got to the Chesapeake Bay area?
14. From the distribution map, what is the most northern part of the Chesapeake Bay that rapas
have been found?
15. What is the control method for rapa whelks that is employed in the Chesapeake Bay area?
Common Reed
16. Where is the Common Reed native to?
17. Why is it considered invasive?
18. What man-made stresses allow the reed to become invasive?
19. What are some things that the Common Reed may be used productively for?
20. Describe the Mechanical/Physical method of trying to control the reed.
21. Describe the Chemical method of trying to control the reed.
Japanese Oysters
22. Describe the oyster disease Dermo.
23. Describe the oyster disease MSX.
24. Why did scientists bring the Japanese oyster over to the Chesapeake Bay?
25. How did the Japanese oysters react to the diseases?
26. Why are some scientists wary about introducing the Japanese species into the Chesapeake
Bay?
27. Do you think that it is a good idea to introduce them into the Chesapeake Bay?
WHY OR WHY NOT?
Snakehead Fish
28. Describe what a Snakehead fish looks like.
29. How big can an adult snakehead get?
30. Describe HOW and WHY a snakehead would leave the water.
31. Describe control methods that have been tried to control the snakehead fish.