Download Venerupis philippinarum, Japanese littleneck clam

 Venerupis philippinarum, Japanese littleneck clam
Robyn Shean
FISH 423: Aquatic Invasion Ecology
Fall 2011
Diagnostic information
Scientific name: Veneroida Veneridae Venerupis
philippinarum
Also known as Tapes philippinarum, Ruditapes
philippinarum, Venerupis japonica
Common names:
Japanese littleneck clam, manila clam, steamer
Figure 2: Varied coloration of shell in Japanese
clam, Japanese carpet shell
littleneck; shows concentric rings, radiating ridges,
and split siphon (USGS 2011).
Physical description and physiology
Venerupis
philippinarum,
white in color, Japanese littlenecks are multicommonly
colored and usually have a purple hue along the
called Japanese littleneck clams, are bivalves
umbo and inner rim of the shell (Figure 2).
similar in size and physical appearance as the
The shells of Venerupis philippinarum have
native littleneck clams Leukoma staminea.
concentric rings across the surface with ridges
Japanese littlenecks have two outer shells
radiating across the rings and outward to the
(valves) connected by a hinge, with internal
edges of the shell. The inside of the shell is
ligaments used to open and close the shells. The
smooth. Japanese littlenecks can grow to 3-4
umbo (also known as the beak) is the oldest part
inches in length as mature adults. All clam
of the clam, and is found along the hinged edge.
species contain internal organs that make up the
They have an oblong shell with a slightly higher
body inside the protective shell. Internal
length to width ratio than the native species
structures include a heart, stomach, gonads,
(Figure 1). While native littleneck clams are off-
kidney, intestines, mouth, abductor muscles, and
gills to aid in respiratory function (Figure 3). As
filter feeders, clams have siphons used for the
intake of water and food, as well as excretion of
waste material. A foot is present as a means of
mobility and the body of the clam is secured to
the shell by a thin membrane called a mantle.
The mantle builds the shell by storing calcium
deposits and secreting the calcium to the inside
Figure 1: Non-native V. philippinarum (left) and native
L. staminea (right) (WDFW 2011).
of the shells.
Figure 3: Diagram of internal structure of Japanese littleneck clam (Source: www.barnegatshellfish.org).
Both native and indigenous littleneck clams can
clams can add rings when stressed or disturbed
retract their siphon and completely close their
(Toba 2005). Japanese littleneck clams can grow
shells. This helps the clam retain moisture when
to a size of 1-2 inches in shell length that is
exposed to the air during low tides and protects
suitable for harvest within 2-3 years of age
against predation. Non-native littleneck clams
(Toba 2005).
can survive out of water for longer periods of
time compared to native littlenecks (WDFW
Life-history and basic ecology
2011).
Life cycle
Material is added to the shells of Japanese
littleneck clams as it grows to help it become
larger and thicker. During winter months when
temperatures drop and food sources are limited,
the clam grows at a slower rate. While some
people think the rings on these clams indicate
age, they are not a good predictor of age as
Bivalves
are
broadcast
spawners.
Female and male adults release sperm and eggs
into the water column where fertilization occurs.
Once fertilized, the eggs develop into freefloating trochophore larvae that are carried in
water
currents
over
several
weeks.
The
trochophore than forms ciliated vellum to assist
with mobility and feeding – this is the veliger
by seawater. Individuals that settle at higher
larval stage of development. In approximately 2-
intertidal zones will feed less often and usually
4 weeks, the clam develops into a peliveliger
be smaller in size.
with a formed foot to assist further with
swimming (Jones 1993). In addition, small
Reproductive strategies
threads are formed (byssal threads) to help the
clam secure itself onto the seafloor once it finds
a suitable substrate to settle on. The substrate is
usually a muddy, sandy, or soft surface the clam
can burrow into with its foot. Burrowing into
the ground allows the animal to find food and be
protected from predators. Once settled, it will
stay in the substrate and continue to grow into a
mature clam. Individuals become sexually
mature between 1-3 years of age, and have a life
span up to 14 years (WDWF 2011).
Japanese littleneck clams are dioecious
– there are male and female individuals, each
producing either egg or sperm. Individuals
become sexually mature in the first to third year
of age. This can vary depending on location and
size of shell. In Hood Canal (Washington state),
research has shown that clams are sexually
mature when shell length is 5-10 mm. However,
most individuals do not spawn until shell length
is at least 20 mm (Holland and Chew 1974).
Spawning can occur either once or twice every
year depending on location and environmental
Feeding habits
factors (Ponurovsky 1992). Spawning usually
All clam species are filter feeders and
occurs between April and October when water
have siphons that protrude out of the shell for
temperatures are warmer. In Hood Canal,
feeding. They take water in through the
spawning in some populations happened during
incurrent siphon, filter and extract food items,
this entire period of time (Holland and Chew
and then excrete the filtered water and waste out
1974).
the excurrent siphon. Japanese littleneck clams
As broadcast spawners, clams generate high
have shorter siphons compared to other clam
numbers of gametes that are released once an
species; this is why these clams are referred to as
individual is sexually mature. High fecundity
littlenecks (Cohen 2005). The siphon tip in
increases the chances for large numbers of
Japanese littleneck clams is split and dark in
larvae
color, whereas the siphon is not split in native
population. Reports indicate Japanese littleneck
littlenecks (Jones et al. 1993).
clam fecundity ranges from 4.32x105 eggs to
Japanese littleneck clams feed on phytoplankton
2.35x106 eggs depending on shell length (Yap
throughout their life cycle. Some species can
1977). In addition to temperature, another cue
filter up to 65 gallons of seawater each day
that initiates spawning is the presence of eggs or
(Toba 2005). Clams can only feed while covered
sperm in the water column (Jones et al. 1993).
and
overall
recruitment
for
the
One study produced results indicating some
natives easier to reach for harvesting (WDFW
Japanese littleneck clam populations in areas of
2011).
the Sea of Japan may exhibit sex reversal
For Japanese littleneck clams, the area in which
(hermaphrodite)
environmental
they can successful settle is dictated by two
conditions (Ponurovsky 1992). In Vostok and
factors – competition and predation at lower
Possjet Bays, all individuals with a shell length
limits and exposure at upper limits (Toba 2005).
less than 15 mm produced sperm during their
Non-native Japanese littleneck clams settle
first breeding cycle. However in subsequent
higher in the intertidal zone and in shallower
spawnings, the number of males and females
depths than native littleneck clams. This can
were equal but there was a greater number of
limit feeding times (they only feed when tide is
females in older clam populations.
in and substrate is submerged) and create greater
due
to
opportunities
Environmental optima and tolerances
Temperature plays a critical role in
for
predation
by
terrestrial
organisms and mortality caused by fluctuations
in temperature.
spawning, growth, and survival of Japanese
littleneck clams. The water must be a certain
Biotic associations
temperature for the males and females to release
Brown ring disease
egg and sperm. Spawning usually occurs
While not seen in Japanese littleneck
between 20-25 degrees C (FAO 2011). While
clam populations in the Pacific Northwest, clams
spawning can be initiated by lower temperature,
in Europe have been regularly affected by a
12 degrees C is the minimum threshold for
bacterium Vibrio tapetis leading to a condition
which this species cannot spawn. The optimal
called brown ring disease (Trinkler et al. 2011).
range for growth is 15-28 degrees C, but
Once infected, a brown deposit forms on the
individuals can survive from 0-35 degrees C for
inner surface of the shells – the clam secretes
short durations. Salinity is another factor that
this substance as a defensive response to the
impacts spawning and survival of this species.
presence of the bacteria. Brown ring disease can
For spawning, optimal salinity levels are
cause problems with shell formation and repair
between 24-25 ppt. This species can survive in
(biomineralisation) and have negative effects on
salinity ranging from 13.5-35 ppt (FAO 2011).
the circulatory system of the clam. High
Japanese littlenecks are shallow burrowers
mortality rates caused by this disease were
usually found 2-4 inches under the ground
reported in France in the 1987 (Trinkler et al.
surface within the high intertidal range. This is
2011).
higher than the zone where native littleneck and
butter clams are found; this can make non-
Several native crab species feed on clams. The
Protozoan parasite infections
been
red rock crab (Cancer productus) is found
detected in Japanese littleneck clam populations
throughout central and southern Puget Sound
in the Pacific Northwest, but these parasites
and Hood Canal and feeds on native and non-
have been seen in clam populations in Japan
native clams in the region. Dungeness crab
(Itoh et al. 2004). Three specific protozoan
(Cancer magister) and the graceful crab (Cancer
parasites detected in Japanese littlenecks in
gracilis) also predate on Japanese littleneck
Japan include Haplosporidium sp. found in the
clams. A newly introduced non-native crab
connective tissues, Marteilia sp. found in the
along the Pacific coast is the European green
digestive gland, and Marteilioides sp. found in
crab (Carcinus maenas), which feeds on clam
the oocytes. These parasites haven’t been shown
species. While effects of this predator on clam
to have negative impacts on the clams, but
populations have yet to be seen in Washington
further research is needed to determine if and
state, there have been significant impacts on
how these parasite infections could negatively
aquaculture populations of Japanese littleneck
affect this species of clam.
clams in California. Research has shown a 40
Protozoan
parasites
haven’t
percent decrease in Japanese littleneck clam
Predation
Seagulls and crows feed on both native
and non-native clams when the tide is out.
Migratory birds, including several species of sea
ducks, predate on clams as an added food source
during the winter months. Caldow and others
investigated the interaction between the nonnative Japanese littleneck clam and a specific
seabird, the Eurasian oystercatcher (Haematopus
harvest in California since establishment of the
European green crab (WDFW 2008).
Moon snails (Polinices lewisii) predate on
littleneck clams by drilling a hole in the clam’s
shell and then feeding on the meat inside. Older
clams have harder shells, so they are less likely
to be preyed on by these snails. Additionally,
some species of seastars and bottom-feeding fish
feed on smaller clams.
ostralegus ostralegus). These seabirds rely on
available food sources, including shellfish, for
Current geographic distribution
survival through the winter and in preparation
for migration in the spring. Modeling of
Distribution in PNW and U.S.
shorebird feeding activities was used to show
Japanese littleneck clams were imported
that Japanese littleneck clams in one invaded
to the Hawaiian Islands from Japan in the early
area reduced over-winter mortality rates of the
part of the century. In the mid-1930s, these non-
oystercatcher (Caldow et al. 2007).
Figure 4: Distribution of Venerupis philippinarum in U.S. and Pacific Northwest (USGS 2011).
native clams were then introduced into the
Yellow Sea, Sea of Japan, the Sea of Okhotsk
Pacific Northwest accidentally in shipments of
and around the South Kurile Islands (Scarlato
Pacific oyster seed (FAO 2011). Japanese
1981). Starting in the early 1900s, these clams
littleneck clams spread quickly and are now
were
found along the west coast of North America
intentionally throughout the world (Figure 5). In
from British Columbia down to the California
addition to being introduced in North America
coast (Figure 4). In British Columbia, Japanese
and Canada, this clam species was introduced in
littlenecks are found in bays and inlets
the Mediterranean and West Atlantic coast
throughout the Strait of Georgia. In Washington
waters in the latter half of the 19th century.
state, these clams are found throughout the
Japanese littleneck clams are now present in
Puget Sound region with an abundance of clam
France, the United Kingdom, Ireland, England,
beds located in Hood Canal.
Tahiti, Italy, Germany, and Scotland. In all of
introduced
both
accidentally
and
these regions, this clam species was introduced
Distribution throughout the world
Japanese littleneck clams are native in
the Philippines, South and East China Seas,
as a commercially harvested crop. Additionally,
trial cultures of V. philippinarum have been
Successful in the Virgin Islands, Tunisia,
purposes. This clam species was introduced in
the Mediterranean and West Atlantic coast
waters in the latter half of the 19th century.
Japanese littleneck clams are now present in
France, the United Kingdom, Ireland, England,
Tahiti,
Italy,
Germany,
and
Scotland.
Additionally, trial cultures of V. philippinarum
have been successful in the Virgin Islands,
Tunisia,
Belgium,
Israel,
and
Russia
(Ponurovsky 1992).
Figure 5: Regions across the world producing
Venerupis philippinarum (FAO 2011).
Invasion process
Belgium, Israel, and Russia (Ponurovsky 1992).
Pathways, vectors and routes of introduction
Live shellfish import is the primary
History of invasiveness
pathway
Japanese
unintentionally
littleneck
introduced
clams
to
the
were
Pacific
Northwest as ‘hitchhikers’ in shipments of
Pacific oysters in the 1930s. The non-natives
were packed in containers of oyster seed shipped
from Japan to Washington state where they then
established and spread along the Washington,
Oregon, and California coasts, and throughout
the Puget Sound. This non-native clam appears
to fill an ecological niche that compliments that
of the native littleneck clam (Becker et al. 2008).
Starting in the early 1900s, Japanese littleneck
clams were introduced to coastal and aquatic
regions throughout the world (Figure 5). Most
regions
with
Japanese
littleneck
for
philippinarum;
the
introduction
specifically,
of
V.
import
of
commercial oysters. Individuals were included
with shipments of Pacific oyster spat from
Japan. Another source of possible introduction
may be through ballast water of ships departing
from regions with populations of this clam
species. As broadcast spawners with a larval
stage beginning the life cycle, individuals are
free-floating and able to drift in water currents
over large areas and be transported through
water brought into a ship’s hull area. Transport
of ships from the Eastern Pacific to the Western
Pacific can occur within a short time, increasing
the likelihood of survival of larvae.
clam
populations are within a similar latitudinal range
Factors influencing establishment and spread
as the U.S (FAO 2011). In many cases,
Because of similarities in environmental
introductions were intentional for aquaculture
conditions between Japanese waters and aquatic
systems in the Pacific Northwest, it was
expel water from their siphons. Harvesting
relatively easy for the non-native clam species to
activities in aquaculture settings, such as
become established quickly after introduction.
dredging, affect ecosystems as well. Sediment is
Additionally, as broadcast spawners, fertilized
released into the water column as clams are
eggs can travel through water currents to
pulled from the substrate. In the Pacific
locations outside of documented established
Northwest, Japanese littleneck clams activities
areas.
are
haven’t been documented as having negative
appropriate (suitable temperature and sandy,
impacts on ecosystem function. However, in
loose substrate), settlement and spread of this
other regions where this species is established,
non-native clam is easily facilitated. Once a
research has shown that this clam has ecological
small population is established, spawning each
affects.
year generates large numbers of potential
This species was introduced into the Venice
recruits due to the high fecundity of this species.
Lagoon in 1983 as an aquaculture crop to boost
If
environmental
conditions
the economy of the region (Pranovi et al. 2006).
Economic impacts
Invasion of the Japanese littleneck clam
into the Pacific Northwest created an economic
boom in the shellfish industry. Washington state
is the leading producer of farmed bivalve
shellfish in the U.S. In 2000, farmed shellfish
harvests generated just under $77 million in
revenue (Puget Sound Partnership 2003). Of
these sales, clams accounted for approximately
$14 million. Japanese littleneck clams are the
leading commercial clam species harvested in
the state, with approximately 4,500 tons
harvested annually (WDFW 2011).
While boosting the economy and generating
revenue, harvest activities have caused severe
stress on the benthic communities and the entire
lagoon ecosystem. The non-native clam spread
throughout the lagoon in which
it was
introduced and expanded into other coastal
areas. Because of the rapid growth of this
species, it has become one of the dominant
species in the lagoon in biomass and abundance,
displacing other native species (Pranovi et al.
2006).
With large numbers of Japanese littleneck clams,
harvest activities have increased and affected the
remaining native clam species that are more
sensitive to dredging and sediment disturbance.
Ecological impacts
Rapid changes to the environment caused by
Burrowing aquatic species affect the
increased harvesting activities can make well-
ecosystem in which they live. Clams disturb
adapted native species more vulnerable to
sediment as they move through the substrate and
pressures
release particles into the water column as they
littleneck clams.
caused
by
non-native
Japanese
As filter feeders, Japanese littleneck clams
organisms. Paralytic shellfish poisoning and
consume phytoplankton and excrete waste
amnesic shellfish poisoning can infect shellfish
(feces, pseudofeces) into the water column. With
and in turn, cause illness in organisms that
extensive populations of these organisms, these
utilize clams as a food source, including humans
activities can affect the chemistry and turbidity
(WDFW 1998). Monitoring toxin levels in
of water in shallow habitats and ‘generate high
shellfish, including clams, can aid fishery
microbial respiration leading to sediment anoxia
agencies in assessing the health of aquatic
that inhibits nitrification and kills benthic fauna’
systems and assist in recovery efforts. Most of
(Pranovi et al. 2006). Another study performed
the time, this involves closure of shellfish
in the Sacca di Goro (Italy) investigated effects
harvesting in affected areas until the algal bloom
of Japanese littleneck clam farming on nutrient
is over.
and respiration levels. Results indicate that
farming Japanese littleneck clams has a strong
Management strategies and control methods
affect on oxygen and carbon dioxide levels and
increased densities of certain bacteria (Bartoli et
al. 2001). These effects could increase the risk
for anoxic conditions in the aquatic environment
and cause harm to benthic organisms. The
presence of clams also stimulates inorganic
nitrogen and phosphorus from sediment into the
water column. Increased circulation of these
nutrients
can
promote
production
of
phytoplankton, but also encourage growth of
some algae species leading to potentially
harmful algal blooms (Bartoli 2001).
Management of the non-native Japanese
littleneck clam is minimal, as this is one of the
top commercial shellfish harvest industries in
Washington state (Puget Sound Partnership
2003). Aquaculture of this species is a major
source of revenue for the region. Harvest of
Japanese littleneck clams in naturalized beds by
private citizens is another source of income for
the state due to revenue generated by the cost of
shellfish licenses.
In addition to providing
revenue as a commercial aquaculture crop, these
clams act as an additional food source for
Indicators of ecological changes in aquatic
migrating seabirds – another benefit of having
systems
this nonindigenous species established within
As filter feeders, clams take in water and
Pacific Northwest aquatic regions.
extract phytoplankton. Any bacteria or toxins are
One problematic area of these non-native clams
also filtered through their system and can
involves harvesting naturalized and cultured
accumulate in the internal organs. This happens
beds. Harvesting clam beds can disrupt the
most often during algal blooms, when certain
ecosystem and create challenges for native
conditions
species. Mechanical and manual harvesting
promote
production
of
these
techniques are used, both of which disturb the
substrate,
displace
native
organisms,
Literature cited
and
increase sediment and nutrient loads in the water
Becker P, Barringer C, Marelli D (2008) Thirty
column.
years of sea ranching Japanese littleneck
Manual harvesting involves raking the clams out
clams
of the substrate and bringing them to the surface
Successful techniques and lessons learned.
where they can be gathered. Mechanical
Reviews in Fisheries Science 16: 44-50
(Venerupis
philippinarum):
harvesting involves dredging by a tractor (Figure
6). The tractor is equipped with a lateral belt that
Caldow RWG, Stillman RA, le V dit Durell,
digs and grades the sandy bottom areas. In
Sarah EA, West AD, McGrorty S, Goss-
dredging the surface floor, whether by manual or
Custard JD, Wood PJ, Humphreys J (2007)
mechanical methods, other organisms are pulled
Benefits to shorebirds of invasion of a non-
from the substrate and nutrients are released
native shellfish. Proceedings of the Royal
from the sediment.
Society B 274: 1449-1455
Cohen, Andrew N (2005) Guide to the Exotic
Species
of
San
Francisco
Bay.
San Francisco Estuary Institute, Oakland,
CA
de Moura Queiros A, Hiddink JG, Johnson G,
Kaiser MJ (2011) Context dependence of
marine
ecosystem
engineer
invasion
impacts on benthic ecosystem functioning.
Biological Invasions 13: 1059-1075
Fisheries and Aquaculture Department (2011)
Database on Introductions of Aquatic
Species
(DIAS).
Fishery
Records
Collections. FIGIS Data Collection. FAO
Fisheries and Aquaculture Department.
Figure 6: Mechanical methods of harvesting
Accessed
29
November
2011:
Japanese littleneck clams with small and large
http://www.fao.org/fishery/culturedspecies/
scale tractors (FAO 2011).
Ruditapes_philippinarum/en
Holland DA, Chew KK (1974) Reproductive
Scarlato OA (1981) Bivalves of temperate
cycle of the Japanese littleneck Clam
waters of the northwestern part of the
(Venerupis japonica) from Hood Canal,
Pacific Ocean. Nauka Press, Leningrad
Washington). Proceedings of the National
Shellfish Association 64: 53:58
Tinkler N, Bardeau JF, Marin F, Labonne M,
Jolivet A, Crassous P, Paillare C (2011)
Itoh N, Momoyama K, Ogawa K (2004) First
Mineral phase in shell repair of Japanese
report of three protozoan parasites (a
littleneck clam Venerupis philippinarum
haplosporidian,
affected b brown ring disease. Diseases of
Marteilioides
Marteilia
sp.)
from
sp.
the
and
Japanese
Aquatic Organisms 93: 149-162
littleneck clam, Venerupis philippinarum in
Japan. Journal of Invertebrate Pathology
88: 201-206
Toba D, Dewey B, King T (2005) Small-scale
clam farming for pleasure and profit in
Washington.
Jones G, Sanford C, Jones B (1993) Japanese
littleneck clams, hatchery and nursery
Program
Washington
Publication
Sea
Grant
WSG-AS
03-02,
Seattle
methods. BC Ministry of Agriculture and
Fisheries
United States Geological Survey (USGS) (2011)
Venerupis philippinarum Fact Sheet. USGS
Melia P, De Leo GA, Gatto M (2004) Density
and temperature-dependence of vital rates
Nonindigenous Aquatic Species Database,
Florida
in the Japanese littleneck clam Tapes
philippinarum: a stochastic demographic
Washington Department of Fish & Wildlife
model. Marine Ecology Progress Series
(2011) Fishing and Shellfishing: Japanese
272: 153-164
littleneck clams.
Ponurovsky SK, Yakovev YM (1992) The
reproductive biology of the Japanese
Washington Department of Fish & Wildlife
littleneck, Tapes philippinarum (A. Adams
(1998) Shellfish of Washington, publication
and Reeve, 1850) (Bivalvia: Veneridea).
FM96-03
Journal of Shellfish Research 11(2): 265277
Washington Department of Fish & Wildlife
(2008) Invasive Species Fact Sheets:
Puget
Sound
Partnership
(2003)
Shellfish
Economy: Treasures of the Tidelands
Carcinus maenas (European green crab).
Aquatic Nuisance Species, Seattle
Yap WG (1977) Population biology of the
Japanese
littleneck
clam,
Tapes
Background in shellfish aquaculture; experience
as a shellfish biologist.
philippinarum, in Kaneoche Bay, Oahu,
Hawaiian Islands. Pacific Science 31(3):
Laura Hoberecht, PhD
223:244
Northwest Regional Aquaculture Coordinator
NOAA’s National Marine Fisheries Service
Phone: 206.526.4453
Other key sources of information
Email: [email protected]
Washington Department of Fish & Wildlife
www.wdfw.wa.gov/fishing/shellfish/clams/Japa
nese littleneck_clams.html
National
Oceanic
Focus on marine aquaculture species,
including
shellfish
and
other
invertebrates, finfish and plants.
and
Atmospheric
Administration (NOAA) Aquaculture Program
http://aquaculture.noaa.gov/
Graham Gillespie, BS
Head of the Intertidal Bivalve, Cephalopod and
Crab Programs
Fisheries and Oceans Canada (DFO)
Washington State Department of Health
Shellfish and Water Protection Programs and
Services
Pacific Biological Station, Nanaimo, British
Columbia
Phone: 250-756-7215
http://www.doh.wa.gov/ehp/sf/default.htm
Email: [email protected]
Leads aquatic invasive species project
The
National
Shellfisheries
Association
(shellfish research)
examining distribution and impacts of
intertidal non-native species on the
http://shellfish.org/
Pacific Coast of Canada.
Washington Sea Grant
Current research and management efforts
http://www.wsg.washington.edu/about.html
Management efforts for the Japanese littleneck
Expert contact information in PNW
Derrick Toba, BS, MS Fisheries
Assistant
Region
Manager,
Department of Natural Resources
Aquatic Region, Shoreline District
Email: [email protected]
clam are not necessary for controlling spread of
this species, as naturalized clam beds are
Washington
harvested
regularly
to
maintain
stable
populations. Hatcheries and nursery systems for
generating seed, larvae, and juvenile clams are
well regulated. To date, fishery agencies are not
engaging in management or control efforts of
this non-native species due to lack of harm or
negative
impacts
within
established
communities. Because this is one of the leading
commercial aquaculture crops in this region,
there is a strong emphasis on maintaining
healthy
hatcheries,
aquaculture
sites,
and
naturalized beds.
The Fisheries and Aquaculture Department
indicates that aquaculture of Japanese littleneck
clams will likely increase either through
expansions in current farmed sites or by new
introductions into suitable recipient areas (FAO
2011). Aquaculture practices include use of
hatcheries to cultivate seed, nursery beds, trays,
cages, bags, and nets (Jones et al. 1993).
Developing methods to reduce the impacts of
aquaculture within an ecosystem is one focus
area at managing effects of this non-native clam.
One possible way to minimize environmental
impacts of aquaculture activities is polyculture,
where multiple species are farmed in one region.
Japanese littleneck clams have become recent
participants in polyculture farms, being raised
with various species of shrimp and fish (FAO
2011). Further research is needed to see if this
method of culturing shellfish can reduce the
impacts on ecosystems.