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)

brady.blake@dfw.wa.gov

and

Allen Pleus

WDFW Aquatic Invasive Species (AIS)

Coordinator

(360) 902-2724

Allen.pleus@dfw.wa.gov

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)