Image: Close up view of Mytilus galloprovincialis.
(http://media.eol.org/content/2013/07/02/05/62258_260_190.jpg)
INVASIVE SPECIES
REPORT Mediterranean Mussel
Mytilus galloprovincialis
Amy Green FISH 423, Autumn 2014
University of Washington
Diagnostic information
Scientific name
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Order: Mytiloida
Family: Mytilidae
Genus: Mytilus
Species: galloprovincialis
(Lamark, 1819)
Common name(s)
Mediterranean mussel
Photos/Detailed illustrations
Figure 1: Close up of Mytilus galloprovincialis, an
invasive mussel in Puget Sound, Washington.
Photo Credit: AquaCase 3.0
(http://www.aquacase.org/Mussels/mussels_chalas
tra/intro.html)
Basic identification key
Mussels have dark blue and black shells
with a pearly interior. They are a bivalve, which
means they have two bilaterally symmetrical
hinged shells that meet together to enclose their
soft body. The shells are elongate and rounded at
the far end, away from the umbo where the
hinge is located. The outer layer of the shell is
covered by periostracum, followed by a
prismatic calcified layer. Often, the periostracum
will erode or peel away, showing different hues
of the prismatic layer.
All Mytilus look very similar and may be
difficult to visually correctly identify to species.
Mytilus galloprovincialis very closely resembles
the native Mytilus trossulus, or Bay Mussel
(Boersma et al., 2006). However, M.
galloprovincialis can be distinguished from the
larger native California mussel (M.
californianus) by its radiating ribs. Koehn
(1991) describes the best method of
discrimination between M. galloprovincialis and
M. edulis as the length of the anterior adductor
mussel scar and hinge plate. The Food and
Agriculture Organization of the United Nations
(2014) states that M. galloprovincialis differs
from M. edulis by the umbones turning
downwards tending to make the basal line of the
shell concave. M. galloprovincialis valves are
higher and less angular on the upper margin and
tend to grow larger. Finally, the M.
galloprovincialis mantle edge is darker,
becoming blue or purple. Successful
identification may require use of genetic
analysis to accurately determine species.
Figure 2: Three Mytilus species illustrating
difficulty in correct visual identification. Genetic
testing is suggested to accurately identify mussel
species. Photo Credit: Linda Schroeder and
Pacific Northwest Shell Club
(http://www.asnailsodyssey.com/LEARNABOUT/
MUSSEL/mussGrow.php)
Life-history and basic ecology
Life cycle
M. galloprovincialis begin as
microscopic larvae, drifting with water currents
for several weeks before settling down to the
benthos (Boersma et al., 2006). Depending upon
water movement, plankton may drift in excess of
200 km or more (Suchanek et al., 1997). After
settling, larvae begin to metamorphose into their
adult form and secrete byssel threads to attach to
hard substrate. This species lives between one to
two years, however, they have the potential to
live up to 20 (Boersma et al., 2006). They are
larger than other species, and can grow up to 15
cm, although typically only 5-8 cm (IUCN/SSC
Invasive Species Specialist Group, 2006). They
also grow rapidly and can reach 70 mm within
their first year (Picker and Griffiths, 2011).
Figure 3: External parts of Mytilus including
valve, foot, byssal threads and siphon. Foot and
byssal threads are used to attach to hard
substrate. The valve houses the internal soft body,
and siphon is used for feeding.
(http://shipfoulingchem409group2.wikispaces.com
/file/view/MusselAnatomy.jpg/474397934/MusselA
natomy.jpg)
Feeding habits
M. galloprovincialis are filter feeders on
tiny phytoplankton and organic matter (FAO,
2014). They feed on tiny food particles by using
their gills to pump water through cilia that move
in the direction of their mouth. In 20 minutes, an
adult Mytilus can filter a liter of water (Boersma
et al., 2006). Filtering the water of nitrogen,
phosphorous and plankton allows sunlight to
penetrate the water column (PCSGA, 2014).
Reproductive strategies
Mussels are broadcast spawners and
release millions of gametes into the water
column when reproductively mature, after about
one year (Branch and Steffani, 2004). Mussels
often grow into beds of individuals upon
settling, coating any hard surface area. Colony
sizes can reach numbers in the millions
(Department of Agriculture, Republic of South
Africa). Recruitment occurs throughout the year
with major settlement from May to September
(FAO, 2014).
Figure 4: Life cycle of Mytilus from trochophore
larvae to spawning adults. After about one year,
mussels are reproductively mature, releasing
millions of gametes into the water (Branch and
Steffani, 2004).
(http://www.clarku.edu/departments/biology/biol2
01/2004/ckammererburnham/Images/life%20cycle
%20diagram.gif)
Environmental optima and tolerances
All Mytilus species attach to hard
surfaces including boat hulls, buoys, floats,
pilings and natural rocky shorelines. M.
galloprovincialis does not tolerate reduced
salinities of 15-20 ppt for extended periods of
time (Brooks, 2007). These mussels are more
commonly found in high salinity and wave
exposed habitats than native mussels in South
Africa. (Skibinski et al., 1983). Branch and
Steffani (2004) state that M. galloprovincialis
has twice the tolerance to air exposure and
dessication than native mussels, making them a
durable and successful invasive species.
Suchanek et al. (1997) found a shift from M.
trossulus to M. galloprovincialis at 40-41
degrees latitude and at similar temperatures
across the west and east Pacific, suggesting that
temperature is a limiting factor.
Biotic associations (pathogens, parasites, and
commensals)
Mytilus species are consumed by snails,
seastars, fish, birds, raccoons, bears, humans,
and other species (Boersma et al., 2006). In the
Pacific Northwest, M. galloprovincialis were
previously difficult to grow in culture because of
a disease (disseminated hemic neoplasia), which
caused their tissue to soften and liquefy before
reaching market size (Boersma et al., 2006). In
the mid-1980s, disease resistant mussels were
discovered in southern California, which lead to
a thriving industry of “super mussels” (Boersma
et al., 2006). In 1999, the world aquaculture
supply of mussels was 1.8 million metric tons,
supplied by 333 metric tons from the United
States. This equates to roughly $6.7 million
(Fishwatch, 2014).
In South Africa, the whelk Nucella cingulate is a
predator of M. galloprovincias but cannot keep
up with such a high settlement rate (Branch et
al., 2004). These whelks have been found to
increase in density where these mussels have
established populations. Typically, predation is a
key factor in regulating mussel populations. Sea
stars are keystone predators that often regulate
mussel populations in Puget Sound. However,
Seastar Wasting Disease has wiped out many
individuals, and it is unknown how mussel
populations will be effected by this release.
Also in South Africa, the endangered African
Black Oystercatcher has been documented to
switch from feeding on native mussels to the
invasive Mediterranean mussel. This may be
because the invasive mussel has taken over
habitat typically used by the native mussels, or
because they grow larger in size and provide
more energy per individual. As a result, these
wading birds’ reproductive potential have
increased following mussel establishment
(Branch et al., 2006). This poses a dilemma to
managers, as Oystercatchers are protected
species, and rely on these invasive mussels as a
food source.
Two organisms, endolithic cyanophyte
Mastigocoleus sp. and lichen Pyrenocolema sp.,
bore on mussels larger than 40 mm, and do not
seem to effect other native mussels as much as
M. galloprovincias in South Africa (Webb &
Korrubel, 1994). Boring weakens the shell,
allowing easy access for other predators.
Calvo-Ugarteburu & McQuaid (1997) found
M.galloprovincialis in newly invaded habitat to
be free of trematodes (parasites such as
Proctoeces maculatus metacercariae and
bucaphalid sporocytsts). The native Perna perna
mussel in South Africa was typically found
infected with 4 species of trematodes. This may
be a form of enemy release, where the mussels
are escaping parasitism by moving to new
habitat. Negative effects of these parasites
include reduced body condition, reduced growth
rate, ease of predation, and loss of water
resulting in desiccation (Calvo, 1998). If
parasites are only attacking native mussels, this
provides more opportunity for the invasive
mussel to establish.
Branch et al. (2004) discovered that M.
galloprovincialis larvae lead to mass mortalities
of the swimming crab Ovalipes trimaculatus.
Larvae settled onto the eyestalks and mouthparts
of the crab, leading to inability to feed. Branch
(unpublished) estimated 95,700 crabs killed
during five different episodes of mass
mortalities; with estimates as high as 2.2 million
for the Southern African coast.
The biggest concern in Washington is mussel
distribution overlaps and hybridization with
native mussels. M. galloprovincialis and
M.trossulus have been found to hybridize near
Whidbey Island, WA, San Francisco Bay, CA,
and San Diego Bay, CA (Suchanek et al., 1997;
Boersma et al., 2006).
Current geographic distribution
M. galloprovincialis is native to the
Mediterranean and Atlantic coast of southern
Europe (Anderson et al., 2002). Figure 5 shows
the current distribution of Mediterranean mussel
across the globe (Branch, 2004).
These mussels are now found in the Pacific
Northwest, California, Oregon, Japan, Southern
Africa, South America (Boersma, et al., 2006),
Hawaii, Hong Kong, Japan, Korea, Mexico,
Great Britain, Ireland (Branch and Steffani,
2004), British Columbia, and Canada (Wonham,
2004). Mediterranean mussels are found to be
the most abundant mussel from Tomales Bay to
San Diego, CA using PCR zoogeographic
methods (Suchanek et al., 1997).
In 1991, Brooks confirmed the presence of these
mussels in Washington by using protein
electrophoresis. 9 enzymes were examined in
846 mussels from WA, and 575 mussels from
Figure 5: Current distribution of M. galloprovincialis across the globe, from it’s native range in the
Mediterranean Sea. These mussels have spread across continents, typically found within ports of call. (Taken
from Branch, 2004).
CA, OR, ME and Prince Edward Island.
Suchanek et al. (1997) identified
M.galloprovincialis and hybrids at Whidbey
Island, and suggested they may have been
offspring of cultured mussels in a nearby
mariculture farm. Taylor Shellfish discontinued
the farm because of high mortality rates
(Anderson et al, 2002). Currently, the
Washington Department of Fish and Wildlife
(Brady, 2014; personal communication) has
documented distribution in Port Townsend,
Discovery Bay, Marrowstone Island, Kilisut
Harbor, Oakland Bay and Hood Canal.
Figure 6 (below) shows the current and
suspected distribution of Mediterranean mussel
in the Pacific Northwest (Boersma et al., 2006).
A more detailed view of distribution in Puget
Sound can be seen in Figure 7 (right).
Figure 6: Distribution map of M. galloprovincialis
in the Pacific Northwest. Darker colors indicate
confirmed presence while lighter blue indicates
suspected presence. (Taken from Boersma et al.,
2006).
In 2002, Anderson et al. only found M.
galloprovincialis where they were likely
repeatedly introduced near mussel farms, the
Port of Seattle, and Bremerton Naval Shipyards.
These scientists found low allele frequency of
the Mediterranean mussel in two sites near Puget
Sound mussel farms, suggesting that they are
unlikely to escape aquaculture and are having
little impact on native M. trossulus. Even where
significant invasive mussels exist, hybrids are
uncommon and have limited potential to
“genetically pollute” local mussels. However,
they do stress that alleles are present where ships
are likely to be either releasing larvae in ballast
water, or adults that grow and biofoul ship hulls.
Figure 7: Mytilus sampling sites in Puget Sound,
Washington. Sites were M. galloprovincialis genes
were detected are in bold and capital. Sites with
only M. trossulus genes are indicated in regular
type. (Taken from Wonham, 2004).
History of invasiveness
In South Africa, the Mediterranean
mussel was first collected in 1970 (Boersma et
al., 2006), and is now found along the entire
west coast and southern half of Namibia (Branch
& Steffani, 2003). The native mussel, A.ater has
been taken over by the invasive because they
settle in similar silt-free habitats (Branch et al.,
2004). The native mussel has slower growth,
lower reproductive output and lower air
tolerance, while the invasive mussel is superior
in all aspects.
In Japan, the first record of M. galloprovincialis
was in 1932 in Kobe Port, Hyogo prefecture.
The route of introduction is suspected to be
ballast water or biofouling. Distribution of the
mussel is now along the entire coast of Japan
(National Institute for Environmental Studies,
see additional sources of information)
Invasion process
Pathways, vectors and routes of introduction
Pathways in which Mediterranean
mussels have been introduced include shipping
activities and aquaculture (Anderson et al.,
2002). Vectors of introduction include deliberate
stocking or planting, ship ballast (water and
soil), hitchhiking on ship hulls and rotors, and
natural drifting mussel culture rafts in which
thousands of animals form into a hanging
population (Boersma et al., 2006).
Geller et al. (1994) identified planktonic larvae
from ballast water of commercial cargo ships
from Japan to Oregon from 1988-1990 and
found that all mussel larvae were M.
galloprovincialis. The mussels hitched a ride
from OR to CA on the Golden Hinde II, a
replica tall ship that sailed down the pacific
coast in the early 1990s. Mediterranean mussels
were found to have settled and grew on the hull
(Carlton and Hodder, 1995).
Factors influencing establishment and spread
Branch & Steffani (2003) calculated a
rate of spread of these mussels of 115 km/year in
South Africa. They are known to establish in
temperate environments. As planktonic larvae
are reliant on water currents for distribution,
they are somewhat limited in spread. In
Washington, Anderson et al. (2002) suggests
that Totten Inlet water currents have kept the
larvae circulating within the inlet, preventing
spread out into the bay.
Hilbish (1994) in an experimental study, found
that M. galloprovincialis has a three-fold higher
feeding rate and slightly elevated metabolic rate
compared to M. edulis. Hilbish also found that
this species grew significantly faster in the field,
allowing the mussel to establish quicker than
native mussels.
Branch et al (2004) states that properties that
make the mussel such a good invasive include
high productivity, scarcity of predators, absence
of parasites, fast growth, high reproductive
output, and having planktotrophic larvae.
Potential ecological and/or economic impacts
Mussel culture rafts are known
elsewhere to change food-web dynamics, water
flow, nutrient, oxygen and microbe levels
(Boersma et al., 2006). Mussels bioaccumulate
biological toxins and industrial pollutants,
allowing them to move up the food web
(Boersma et al., 2006). M. galloprovincialis
shells are larger and predators may either have
difficulty opening them, or may need to eat less
to gain the same energy intake (Anderson et al.,
2002).
Because they are a benthic species, these
mussels may displace other benthic organisms
by taking up the limiting resource of hard
substrate. They can provide a “substitute
stratum” by allowing growth on top of the
mussels themselves, but it is no replacement of
the benthos (Branch et al., 2004).
Some benefits of these mussels include
providing another food source for the
endangered African Black Oystercatcher
(Haematopus moquini). Mussels also filter and
clear the water from suspended phytoplankton,
allowing sunlight to reach aquatic plants, such as
seagrasses like eelgrass.
However, these mussels were also found to
cause mass mortalities of the swimming crab
(Branch et al., 2004). It is unknown whether
other crab species will be similarly effected by
large populations of Mediterranean mussel.
M. galloprovincialis have been intentionally
stocked in Puget Sound for aquaculture
(Anderson et al., 2002). Farming provides
economic benefits to the growers and to the
state. Thousands of jobs are created,
contributing more than $110 million a year to
the west coast economy (PCSGA, 2014).
Shellfish farming can only occur in water
certified under the National Shellfish Sanitation
Program (NSSP) out of the Food and Drug
Administration. Water quality is closely
monitored to ensure that contamination doesn’t
occur (PCSGA, 2014).
Figure 8: Floating mussel rafts used in
aquaculture by Taylor Shellfish in Puget Sound,
Washington. Escapes from aquaculture pose a
threat of introduction of M. galloprovincialis
mussels into Puget Sound, Washington.
(http://wtseafood.com/rafting-with-mussels-on-
puget-sound/)
Management strategies and control methods
In Washington, M. galloprovincialis are
a “regulated aquatic animal species” similar to
pacific oysters Crassostrea gigas and manila
clams Venerupis philippinarum (Boersma et al.,
2006). All three mussel species (M. trossulus, M.
edulis and M. galloprovincialis) are legally
farmed from local hatchery broodstock,
however, they cannot be released into
Washington waters. (Boersma et al., 2006). The
Washington Department of Fish and Wildlife
issues transport and import permits of seed in
Puget Sound (Brady, personal communication).
M. galloprovincialis are not listed on the aquatic
invasive species webpage of WDFW
(http://wdfw.wa.gov/ais/molluscs.html).
Unfortunately, the difficulty in control, or even
tracking distribution lies in distinguishing the
mussel species apart from natives without
relying on genetic testing, which takes time and
money.
WDFW does manage the Ballast Water Program
under water management laws Chapter 77.120
RCW (Washington State Legislature, 2004). All
vessels three hundred grow tons or more are
required to file a ballast water reporting form at
least 24 hours prior to arrival, and to not
discharge ballast water in waters of the state
except as authorized. Discharge of water into the
state is only authorized if there has already been
an open sea exchange, or if the water has been
treated. There may be penalties of up to $27,500
each day of violation.
Literature cited
Anderson, A.S., Bilodeau, A.L., Gilg, M.R. and
Hilbish, T.J. 2002. Routes of introduction of
the Mediterranean mussel (Mytilus
galloprovincialis) to Puget Sound and Hood
Canal. Journal of Shellfish Research.
21(1):75-79.
Branch, G.M. and Steffani, C.N. 2004. Can we
predict the effects of alien species? A case-
history of the invasion of South Africa
by Mytilus galloprovincialis (Lamarck).
Journal of Experimental Marine Biology
and Ecology. 300:189-215.
Brooks, K.M. 1991. The genetics and
epizootiology of hemic neoplasia in Mytilus
edulis. Ph.D. Thesis. University of
Washington.
Brooks K.M. 2007. The frequency of Mytilus
edulis galloprovincialis alleles in
Washington state marine waters where the
species is commercially cultivated. In
review.
Boersma, P.D., Reichard, S.H., Van Buren, A.N.
2006. Invasive species in the Pacific
Northwest. University of Washington.
Seattle.
Calvo-Ugarteburu, G., and McQuaid, C.D. 1998.
Parasitism and introduced species:
epidemiology of trematodes in the intertidal
mussels Perna perna and Mytilus
galloprovincialis. Journal of Experimental
Marine Biology and Ecology. 220: 47-65.
Carlton, J.T. 1989. Man’s role in changing the
face of the ocean: biological invasions and
implications for conservation of near-shore
environments. Conservation Biology. 3(3):
265-273.
Carlton, J.T. and Geller, J.B. 1993. The global
transport of nonindigenous marine
organisms. Science. 261(5117):78-82.
Carlton, J.T. and Hodder, J. 1995. Biogeography
and dispersal of coastal marine organisms:
experimental studies on a replica of a 16th-
centure sailing vessel. Marine Biology. 121:
721-730.
Ceccherelli, V.U. and Rossi, R. 1984.
Settlement, growth and production of the
mussel Mytilus galloprovincialis. Marine
Ecology – Progress Series. 16: 173-184.
Geller, J.B., Carlton, J.T., Powers, D.A., 1994.
PCR-based detection of mtDNA haplotypes
of native and
invading mussels on the northeastern Pacific
coast: latitudinal patterns of invasion.
Marine Biology. 119: 243-249.
Geller, J. 1999. Decline of a native mussel
masked by sibling species invasion.
Conservation Biology. 13: 661-664.
Hilbish, T.J., Bayne, B.L., and Day, A. 1994.
Genetics of physiological differentiation
within the marine mussel genus Mytilus.
Evolution. 48(2): 267-286.
Hilbish, T.J., et al. 2010. Historical changes in
the distributions of invasive and endemic
marine invertebrates are contrary to global
warming predictions: the effects of decadal
climate oscillations. Journal of
Biogeography. 37: 423-431.
Picker, M.D. & Griffiths, C.L. 2011. Alien and
Invasive Animals – A South African
Perspective. Randomhouse/Struik Cape
Town.
Rensel, M., Elliott, J. & Wimberger, P. 2005.
Will the introduced mussel Mytilus
galloprovincialis outcompete the native
mussel M.trossulus in Puget Sound? A study
of relative survival and growth rates among
different habitats. Puget Sound Georgia
Basin Research Conference.
Skibinski, D. 0. F., J. A. Beardmore, and T. F.
Cross. 1983. Aspects of the population
genetics of Mytilus (Mytilidae: Mollusca) in
the British Isles. Biological Journal of the
Linnean Society. 19:137-183.
Suchanek, T.H., Geller, J.B., Kreiser, B.R. and
Mitton, J.B. 1997. Zoogeographic
distributions of the sibling species Mytilus
galloprovincialis and M. trossulus (Bivalvia:
Mytilidae) and their hybrids in the North
Pacific. Biological Bulletin. 193(2): 187-
194.
Webb, S.C., Korrubel, J.L., 1994. Shell
weakening in marine mytilids attributable to
blue-green alga Mastigocoleus
sp. (Nostochopsidaceae). Journal of
Shellfish Research. 13:11-17.
Wonham, M.J. 2004. Mini-review: Distribution
of the Mediterranean mussel Mytilus
galloprovincialis (Bivalvia:Mytilidae) and
hybrids in the Northeast Pacific. Journal of
Shellfish Research. 23(2): 535-543.
Other key sources of information
Department of Agriculture, Forestry and
Fisheries, Republic of South Africa
(http://www.nda.agric.za/doaDev/sideMenu/fish
eries/03_areasofwork/Aquaculture/BIODIVERS
ITY/M.%20galloprovincialis%20BRBA%2012.
12.12.pdf)
This document describes M.
galloprovincialis biology, introduction,
establishment and spread throughout South
Africa.
Encyclopedia of Life
(http://eol.org/pages/449961/overview)
This website provides a nice summary of M.
galloprovincialis biology, including pictures
and distribution maps, resources and
literature.
FishWatch, NOAA
(http://www.fishwatch.gov/seafood_profiles/spe
cies/mussels/species_pages/blue_mussel_farmed
.htm)
This website gives a simple overview of
mussel aquaculture and farming.
Fisheries and Aquaculture Department, Food
and Agriculture Organization of the United
Nations
(http://www.fao.org/fishery/culturedspecies/Myt
ilus_galloprovincialis/en)
This website also provides substantial
information on M. galloprovincialis
biology, reproduction and distribution.
Global Invasive Species Database
(http://www.issg.org/database/species/ecology.a
sp?si=102&fr=1&sts=sss&lang=EN)
This website provides substantial
information on M. galloprovincias from the
IUCN/SSC Invasive Species Specialist
Group. Subsections include ecology,
distribution, management, impact, and
references.
Invasive Species of Japan
(http://www.nies.go.jp/biodiversity/invasive/DB
/detail/70290e.html)
This website provides a short summary of
M. galloprovincias distribution in Japan.
Pacific Coast Shellfish Growers Association
(http://pcsga.org/ecosystem-services/)
This website represents shellfish farmers
and describes farming practices and
ecosystem benefits.
Washington State Legislature, Ballast Water
Management Chapter 77.120 RCW
(http://apps.leg.wa.gov/RCW/default.aspx?cite=
77.120)
Washington state rules and regulations on
ballast water practices.
Washington State Legislature, Invasive Species
Chapter 77.135 RCW
(http://app.leg.wa.gov/rcw/default.aspx?cite=77
.135)
Washington state rules and regulations on
invasive species.
Expert contact information in PNW
Washington Department of Fish and
Wildlife
Brady Blake
Shellfish Disease and Pest Prevention
Olympia Oyster Restoration
Intertidal Shellfish Enhancement
(360) 302-3030 (ext. 301)
and
Allen Pleus
WDFW Aquatic Invasive Species (AIS)
Coordinator
(360) 902-2724
Current research and management efforts
Because M. galloprovincialis is a
regulated aquatic animal species (Regulated type
A species), the Washington Department of Fish
and Wildlife allows permitted release into state
waters for aquaculture purposes (Pleus, personal
communication). RCW 77.135.030 states that
regulated type A species are “nonnative aquatic
animal species that pose a low to moderate
invasive risk that can be managed based on
intended use or geographic scope of
introduction, have a beneficial use, and are a
priority for department-led or department-
approved management of the species’ beneficial
use and invasive risks” (Washington State
Legislature, 2014). RCW 77.135.040 states that
regulated type A species “may not be introduced
on or into a water body or property without
department authorization, a permit, or as
otherwise stated by rule” (Washington State
Legislature, 2014).
Currently, the Washington Department of Fish
and Wildlife Shellfish Disease and Pest
Prevention Unit manages M. galloprovincialis
under RCW 77.12.047 section h; classifying
species of marine and freshwater life as food
fish or shellfish (Washington State Legislature,
2014). The list of species classified as shellfish,
including M. galloprovincialis is in WAC 220-
12-020 (Washington State Legislature, 2014).
M. galloprovincialis is defined as an establish
species, that has been propagated through
aquaculture for at least ten years in Washington,
or a species naturally reproducing within
Washington (WAC 220-77-020; Washington
State Legislature, 2014). As such, WAC 220-77-
040 subsection three states that establish species
from existing import areas with current disease
free tissue certification from areas of origin free
of Class A shellfish diseases are eligible for
continue importation (Washington State
Legislature, 2014). Every three years a disease
free tissue certification must be submitted. The
department can waive the certification
requirement if there is sufficient evidence that
the source area is free of Class A disease. If
reports are made of disease at the source
location, addition disease free certification may
be required. Subsection four describes that
established species from new areas of origin are
eligible for import if health history
documentation and certification are submitted.
Imports originating from outside the west coast
commerce region requires initial quarantine.
The only public fishery for mussels is for
recreational personal use, limited to 10 pounds
in the shell, in the aggregate (WAC 220-56-310;
Washington State Legislature, 2014). The term
“Mussels” in the fishery is includes M.
trossulus, M. californianus and M.
galloprovincialis. Brady (WDFW; personal
communication) states that overall harvest effort
in this fishery for mussels is minute and is not
actively monitored or managed.
Most of the research on M. galloprovincialis is
from South Africa, where the invasive mussel
has dominated native mussel habitat. Impacts on
the Pacific Northwest are yet to be studied
(Boersma et al., 2006). As this species has a
history of invasion and taking over habitat from
native mussels, it’s important to understand the
potential economic and ecologic effects this
species may have on the Puget Sound
ecosystem. However, because it is a farmed
shellfish bringing in millions of dollars and
thousands of jobs, any change in management
will most likely be met with resistance.
Figure 9 shows the predicted global distribution
of M. galloprovincialis in the year 2050. In
comparison to the distribution map from Branch
(2004), the mussels will spread down the
western coast of North and South America, all
along Europe, down the eastern China coast, all
along the Austrailian coast, and spread to New
Zealand. Further research and observation will
show how this extremely successful invasive
species will effect other marine ecosystems.
Figure 9: Predicted global distribution of M. galloprovincialis in 2050. Red colors indicate 0.80-1.00 relative
probability of occurrence. Yellow colors indicate 0.01-0.19 probability of occurrence. These mussels originate
from the Mediterranean Sea, and have spread to various other countries through ballast water, biofouling,
and intentional introduction for aquaculture. Photo Credit: Encyclopedia of Life
(http://eol.org/data_objects/19122361)
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