(DRAFT) - Taxonomy
Species Manila clam
Species Id M060015
Date 26 AUG 96

TAXONOMY

NAME - Manila clam

OTHER COMMON NAMES - Japanese cockle, Japanese littleneck, Manila cockle, Manila littleneck, Philippine cockle, steamer and asari

ELEMENT CODE -

CATEGORY - Aquatic Molluscs

PHYLUM AND SUBPHYLUM - Mollusca,

CLASS AND SUBCLASS - Bivalvia,

ORDER AND SUBORDER - Veneroida,

FAMILY AND SUBFAMILY - Veneridae,

GENUS AND SUBGENUS - Venerupis,

SPECIES AND SSP - japonica,

SCIENTIFIC NAME - Venerupis japonica

AUTHORITY -

TAXONOMY REFERENCES - 01

Taxonomy - 1 (DRAFT) - Status
Species Manila clam
Species Id M060015
Date 26 AUG 96

STATUS

Coded Status
Commercial
Commercial/consumption
See Comments

REFERENCES FOR STATUS - 01

COMMENTS ON STATUS -
Commercial: The Manila clam is the second-most important commercial clam
species on the Pacific coast of North America. It is primarily sold as a
fresh product. About 500 t have been landed annually in Washington since
1975. Presently, only a limited commercial Manila clam harvest exists in
California or Oregon. Nearly all Pacific coast commercial harvest of this
species comes from Washington and British Columbia. In Washington, it is
harvested year around by diggers using forks, rakes, clam hacks, and
hydraulic dredges. This harvest occurs on private and state tide lands, for
which diggers pay a royalty or "stumpage fee" according to the weight
landed. Harvest of this species is often aligned with oyster growers, who
also participate in a Manila clam fishery. Minimum commercial size is 38 mm
shell length (SL). Because of the strong market demands and good biological
attributes, aquaculture of this species has been initiated. *01*

Recreational: This species is highly prized by recreational diggers because
of its good taste and ease of capture. It is one of the most important
recreationally dug clams on the Pacific coast. Clammers harvest Manila clams
year-round during low tide periods by hand or using a fork, pick, rake,
shovel,or garden trowel. It is so heavily harvested in some areas of Puget
Sound, Washington, that it has been almost eliminated. Sport harvesting of
this species does occur in San Francisco Bay, California, despite the
possibility of harvesting clams contaminated by urban wastes and the lack of
offficial authorization.*01*

Indicator of Environmental Stress: The Manila clam is highly tolerant of
pollution and it may accumulate large amounts of pollutants that are harmful
to humans. Hence, many waters are closed to the harvest of this species due
to urban waste water and industrial contamination (primarily coliform
bacteria). Only recently have limited areas in San Francisco Bay been open
for Manila clam harvest.*01*

Status - 1 (DRAFT) - Distribution
Species Manila clam
Species Id M060015
Date 26 AUG 96

DISTRIBUTION

Distribution - 1 HABITAT ASSOCIATIONS

LAND USE -
Bays and Estuaries

REFERENCES FOR LAND USE - 01

NATIONAL WETLAND INVENTORY CODES

NWI NWICLS NWIMOD NWISPEC

Estuarine, intertidal N 4
Estuarine, intertidal N 4

REFERENCES FOR NWI - 01

COMMENTS ON HABITAT ASSOCIATIONS -
Habitat Type: The species is found from the intertidal zone to depths of
about 10 m, but is primarily found at 0.9-2.4 m above mean lower low water
(MLLW). It is not found subtidally in British Columbia.*01*

Substrate: An ideal substrate appears to consist of gravel (much of which
is <25 mm in diameter), sand, some mud (4-5%), and shell. Beaches having
this type of substrate are often relatively stable, and occur in many
protected areas of Pacific Northwest inlets and bays. However, Manila clams
can inhabit a wide range of substrates. Dense concentrations of Manila
clams have been found in substrates ranging from primarily sand to mud.
Additions of pea gravel and small rock on Manila clam beds can enhance
settlement.

Physical/Chemical Characteristics: The Manila clam is found in
mesohaline-euhaline waters. Optimum salanities for larval development are
20-30 ppt. Optimum temperatures for larval development are 23-25 degrees C,
but they can withstand temperatures of 0-36 degrees C. Optimum conditions
for adult and juvenile growth are 28 ppt salinity (range of 24-31 ppt), 16
degrees C (range of 13-21 degrees C), and a food suspension density of 55
mg/l (ranges of 10-135 mg/l). Prolonged salinities below 10 ppt are lethal.
Optimum tidal level appears to be 1.5-2.5 m above MLLW. Small clams do not
appear to grow during the winter when temperatures are < 10 degrees C. The
Manila clam requires temperatures > 14-15 degrees C for maturation,
spawning, and larval development. Juvenile and adult clams require maximum
summer temperatures greater than about 12 degrees C to survive.
Steeply-sloped beaches are not good Manila clam habitat and water currents
play a major role in regulating clam productivity. Currents remove waste,
supply food and oxygen, distribute spat, and may redistribute young
clams.*01*

Migrations and Movements: Larvae are carried by currents into appropriate
areas for settlement. Convergences and eddies often concentrate larvae.
Larvae attach a byssus thread to a pebble or shell during settlement.*01*

ANIMAL/PLANT SPECIES ASSOCIATIONS -
The Manila clam often occurs with Pacific littleneck clam (Protothaca
staminea), butter clam (Saxidomus giganteus), softshell (Mya arenaria),
Macoma spp. clams, and other estuarine infauna. Pinnotherid crabs are common
commensals within the mantle cavity of Manila clams.*01*
Predation: Important predators include: the moonsnails (Polinices spp.),
rock crabs (Cancer spp.), shore crabs, rock sole (Lepidopsetta binineata),
English sols (Pleuronectes vetulus), starry flounder (Platichthys
stellatus), pile perch (Rhacochilus vacca), shiner perch (Cymatogaster
Habitat Associations - 1 aggregata), starfish (Pisaster spp.), ducks and scoters. Nematodes and other
meiofaunal predators may prey heavily on newly-setting spat.*01*

Habitat Associations - 2 (DRAFT) - Food Habits
Species Manila clam
Species Id M060015
Date 26 AUG 96

FOOD HABITS

TROPHIC LEVEL -
FILTERER

REFERENCES FOR TROPHIC LEVEL - 01

LIFESTAGE FOOD FOOD PART
General Phytoplankton Not Specified
General Detritus Not Specified

REFERENCES FOR GENERAL FOOD - 01

COMMENTS ON FOOD -
The Manila clam is a nonselective suspension feeder. Food particles are
inhaled with water through the inhalant siphon, trapped by the gill, sorted
by the palps, and passed to the mouth.*01*

Food consists of suspended detritus and phytoplankton. *01*

Food Habits - 1 (DRAFT) - Environment Associations
Species Manila clam
Species Id M060015
Date 26 AUG 96

ENVIRONMENTAL ASSOCIATIONS

G = General A = Adult
LIM = Limiting RA = Resting Adult
J = Juvenile FA = Feeding Adult
RJ = Resting Juvenile BA = Breeding Adult
FJ = Feeding Juvenile P = Pupae
L = Larvae E = Egg
RL = Resting Larvae
FL = Feeding Larvae

LIFESTAGE ENVIRONMENTAL ASSOCIATIONS
A Water Temperature: Between 15-21 degrees C
A Water Temperature: Specified in Comments
A
A
A
A Substrate: Mud or silt
A Substrate: Sand
A Substrate: Specified in Comments
A Relation to Substrate: Occurs in substrate [penetrating]
A Relation to Substrate: Specified in Comments
A Bottom Type [Aquatic]: Gravel
A Bottom Type [Aquatic]: Sand
A Bottom Type [Aquatic]: Mud or silt
A Bottom Type [Aquatic]: Specified in Comments
A Water Depth Preference: Less than 1 ft.
A Water Depth Preference: 1-5 ft.
A Water Depth Preference: 5-10 ft.
A Water Depth Preference: 10-25 ft.
A Water Depth Preference: 25-50 ft.
A Tidal inundation frequency/ duration: specified in comments
A Estuarine habitat zone: bay
A Estuarine habitat zone: sound
A Estuarine habitat zone: offshore
A Estuarine habitat zone: specified in comments
A Currents: tidal
A Currents: specified in comments
J
J Water Temperature: Between 21-27 degrees C
J

REFERENCES FOR ENVIRONMENTAL ASSOC_ - 01

REFERENCES FOR LIMITING ENVIRONMENTAL ASSOC_ - 01

COMMENTS ON ENVIRONMENTAL ASSOCIATIONS -
Substrate: An ideal substrate appears to consist of gravel (much of which
is <25 mm in diameter), sand, some mud (4-5%), and shell. Beaches having
this type of substrate are often relatively stable, and occur in many
protected areas of Pacific Northwest inlets and bays. However, Manila clams
Environment Associations - 1 (DRAFT) - Environment Associations
Species Manila clam
Species Id M060015
Date 26 AUG 96

can inhabit a wide range of substrates. Dense concentrations of Manila
clams have been found in substrates ranging from primarily sand to mud.
Additions of pea gravel and small rock on Manila clam beds can enhance
settlement.

COMMENTS ON LIMITING ENVIRONMENTAL ASSOC_ -
The Manila clam requires temperatures > 14-15 degrees C for maturation,
spawning, and larval development. Juvenile and adult clams require maximum
summer temperatures greater than about 12 degrees C to survive.

Environment Associations - 2 (DRAFT) - Life History
Species Manila clam
Species Id M060015
Date 26 AUG 96

LIFE HISTORY

Reproduction: The Manila clam is gonochoristic, oviparous, and iteroparous,
It is a broadcast spawner, expelling gametes from the exhalant siphon; eggs
are fertilized externally.*01*

Mating/Spawning: In Japan, spawning occurs both in the spring and autumn. In
Kasaoka, Japan, the Manila clam spawns from early May to July and then again
between early November and late December. Other Japanese studies reveal
spawing times from early March to mid-May and from late October to early
november. In Washington's waters, the Manila clam spawns once per year,
usually between May and September (typically peaking during June and July).
Spawning apparently does not take place at water temperatures below 15
degrees C.*01*

Fecundity: unknown.*01*

Growth and Development: Eggs are spherical and 0.06 mm in diameter.
Embryonic development is indirect and external.*01*

Age and Size of larvae: Larvae range from 0.06 mm to 0.19-0.24 mm in length.
A ciliated, motile, trochophore larvae froms within 24-48 hours after
fertilization at 13-16 degrees C. The veliger needs about 3-4 weeks before
metamorphosing to spat (setting juveniles). The duration of larval stages is
dependent on temperature and food availability.*01*

Juvenile Size Range: At settlement, clams range from 0.190-0.235 mm SL, and
reach 15 mm SL (range 12-20) before becoming sexually mature.*01*

Age and Size of Adults: Some Manila clams may mature at 15 mm SL. Growth
rates vary considerably among geographic locations. One-year old clams are
reported to be 8 mm in SL in Hokkaido, 18 mm SL in the Inland Sea, 27 mm SL
in Southern Japan, 24 mm SL in Hood Canal, Washington, and 10-15 mm SL in
the Strait of Georgia, British Columbia. Growth is also dependent upon the
tidal level clams inhabit, with growth often lower at higher tidal levels.
Clams take 16-22 months to reach market size in Washington, and about 24
months in California. However, they mail need 3-4 years before reaching
legal size in British Columbia. Manila clams also grow more slowly in
overcrowded conditions. The maximum age is probably 7-10 years.*01*

Life History - 1 (DRAFT) - Management Practices
Species Manila clam
Species Id M060015
Date 26 AUG 96

MANAGEMENT PRACTICES

RESULT MANAGEMENT PRACTICE

Beneficial Regulating harvest of species being described
Beneficial Public education - publicity
Beneficial Installing protective nets
Beneficial Maintaining undisturbed/undeveloped areas
Beneficial Mariculture activities
Beneficial
Adverse Dredging
Adverse Underwater explosions
Adverse Underwater mining
Adverse Controlling pollution [thermal, chemical, physical]

REFERENCES FOR BENEFICIAL MANAGEMENT PRACTICES - 01

REFERENCES FOR ADVERSE MANAGEMENT PRACTICES - 01

COMMENTS ON MANAGEMENT PRACTICES -
Indicator of Environmental Stress: The Manila clam is highly tolerant of
pollution and it may accumulate large amounts of pollutants that are harmful
to humans. Hence, many waters are closed to the harvest of this species due
to urban waste water and industrial contamination (primarily coliform
bacteria). Only recently have limited areas in San Francisco Bay been open
for Manila clam harvest.*01*

Commercial: The Manila clam is the second-most important commercial clam
species on the Pacific coast of North America. It is primarily sold as a
fresh product. About 500 t have been landed annually in Washington since
1975. Presently, only a limited commercial Manila clam harvest exists in
California or Oregon. Nearly all Pacific coast commercial harvest of this
species comes from Washington and British Columbia. In Washington, it is
harvested year around by diggers using forks, rakes, clam hacks, and
hydraulic dredges. This harvest occurs on private and state tide lands, for
which diggers pay a royalty or "stumpage fee" according to the weight
landed. Harvest of this species is often aligned with oyster growers, who
also participate in a Manila clam fishery. Minimum commercial size is 38 mm
shell length (SL). Because of the strong market demands and good biological
attributes, aquaculture of this species has been initiated. *01*

Steeply sloped beaches are not good Manila clam habitat. *01*
Management Practices - 1 (DRAFT) - Management Practices
Species Manila clam
Species Id M060015
Date 26 AUG 96

Additions of pea gravel and small rock on Manila clam beds can enhance
settlement.*01*

Plastic netting on beaches improves settlement and growth.*01*

Waves and water currents play a major role in regulating clam productivity.
Currents remove waste, supply food and oxygen, distribute spat, and may
redistribute young clams.*01*

Factors Influencing Populations: Spat settlement areas are dependent on
currents and substrates. Wave damage, extreme temperatures, and siltation
can adversely affect populations sizes. Extreme substrate temperatures
during winter and summer are potentially lethal. High densities of adult
clams may decrease the ability of spat to settle. Most mortaility appears to
occur within the first 2 months after settlement. Losses of newly settled
spat are probably a result of predation, starvation, and climatic
conditions. Because fo good market conditions, numerous aquaculture ventures
are being established or considered. This species' northern distribution is
probably limited by cold water temperatures. Its southern distribution may
be limited by the high salinities and substrate structure of southern
California bays and estuaries.*01*

Management Practices - 2 (DRAFT) - References
Species Manila clam
Species Id M060015
Date 26 AUG 96

References

01 Emmett, R. L., S. L. Stone, S. A. Hinton, and M. E. Monaco. 1991
Distribution and abundance of fishes and invertebrates in west coast
estuaries, Volume II: species life history summaries. ELMR Rep. No. 8.
NOAA/NOS Strategic Environmental Asessments Division, Rockville, MD,
329p.

References - 1