1 V8e!lands Research Center

’ .:ti L:I~ Wtldlife &IV&

’ ::sjundme Bwkvard

iiayt.ttc, La, 70506

FWSlOBS-82111.23

July 1984

Species Profiles: Life Histories and

Environmental Requirements of Coastal

and Invertebrates (North Atlantic)

AMERICAN OYSTER

TR EL-82-4

Library

Natlopal Wetlands Research Center

U. S, Fish and Wlldllf& Service

700 Calundome Boulevard ~_ --_

Lafayefie, La. 70506

Fishes

QL

155

.S63

no.82-

11.23

Fish and Wildlife Service

U.S. Department of the Interior

Coastal Ecology Group

Waterways Experiment Station

U.S. Army Corps of Engine&s

FWS/OBS-82/11.23

TR EL-82-4

July 1954

Species Profiles: Life Histories and

Environmental Requirements of Coastal Fishes and Invertebrates

(North Atlantic)

AMERICAN OYSTER

Mark A. Sellers

Program in Oceanography

University of Maine at Orono

Ira C. Darling Center

Walpole, ME 04573

and

Jon G. Stanley

Maine Cooperative Fishery Research Unit

313 Murray Hall

University of Maine

Orono, ME 04469

Project Manager

Larry Shanks

Project Officer

Norman Benson

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

1010 Gause Boulevard

Slidell, LA 70458

Performed for

Coastal Ecology Group

Waterways Experiment Station

U.S. Army Corps of Engineers

Vicksburg, MS 39180

and

National Coastal Ecosystems Team

Division of Biological Services

Research and Development

Fish and Wildlife Service

U.S. Department of the Interior

Washington, DC 20240
This series should be referenced as follows:

U.S. Fish and Wildlife Service. 1983-19 . Species profiles: life histories

and environmental requirements of coastal fishes and invertebrates. U.S. Fish

Wildl. Serv. FWS/OBS-82/11. U.S. Army Corps of Engineers, TR EL-82-4.

This profile should be cited as follows:

Sellers, M.A., and J. G. Stanley. 1984. Species profiles: life histories and

environmental requirements of coastal fishes and invertebrates (North Atlantic) -- American oyster. U.S. Fish Wildl. Serv. FWS/OBS-82/11.23. U.S. Army

Corps of Engineers, TR EL-82-4. 15 pp.
k

PREFACE

This species profile is one of a series on coastal aquatic organisms,

principally fish, of sport, commercial, or ecological importance. The profiles

are designed to provide coastal managers, engineers, and biologists with a brief

*comprehensive sketch of the biological characteristics and environmental requirements of the species and to describe how populations of the species may be

expected to react to environmental changes caused by coastal development. Each

profile has sections on taxonomy, life history, ecological role, environmental

requirements, and economic importance, if applicable. A three-ring binder is

used for this series so that new profiles can be added as they are prepared. This

project is jointly planned and financed by the U.S. Army Corps of Engineers and

the U.S. Fish and Wildlife Service.

Suggestions or questions regarding this report should be directed to:

Information Transfer Specialist

National Coastal Ecosystems Team

U.S. Fish and Wildlife Service

NASA-Slide11 Computer Complex

1010 Gause Boulevard

Slidell, LA 70458

or

U.S. Army Engineer Waterways Experiment Station

Attention: WESER

Post Office Box 631

Vicksburg, MS 39180

iii
-1

CONTENTS

Page

iii

V

Vi

PREFACE ..................................

CONVEYSION TABLE .............................

ACKNOWLEDG!'lENTS ..............................

NO~~ENCLATURE/TAXONOMY/RANGE ........................

ilORPHOLOGY/IDENTIFICATION AIDS ......................

REASON FOR IKLUSION IN SERIES

LIFE HISTORY .... . .... : : : :.: : : : : : : : :

..................

Spawiny ................................

Larvae

&Juvenile;

................................

Adult . . : l

..............................

GROWTH CHARACT;RiSiI;S' : : : : : : : : : : : : : : : : :

.........

COMMERCIAL HARVEST ................... : :

........

:

....

Population Dyrwnics ...........................

ECOLOGICi1L ROLE ..............................

Et4VIRO?QIENTAL REQUIREMENT'; ........................

Terlgerdture ...............................

Salinities ...............................

iidbi tat .................................

Other Environmental Factors .......................

1

1

2

2

2

3

3

4

4

5

5

8

8

8

9

1 0

1 0

11 LITERATURE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . , . I L

iv
Multiply

millimeters (mm)

centirieters (cm)

meters (m)

kilometers (km)

square meters (m2)

square kilometers (km2)

hectares (ha)

liters (1)

cubic meters (m')

cubic meters

milligrams (mg)

grams (9)

kilograms (kg)

metric tons (t)

umetric tons

kilocalories (kcal)

Celsius degrees

inches 25.40 millimeters

inches 2.54 centimeters

feet (ft) 0.3048 meters

fathoms 1.829 meters

miles (mi) l.GO9 kilometers

nautical niles (nmi) 1.852 kilometers

square feet (ft2)

acres

square miles (mi2)

0.0929 square meters

0.4047 hectares

2.590 square kilometers

gallons (gal) 3.785

cubic feet (ft3) 0.02831

acre-feet 1233.0

liters

cubic meters

cubic meters

ounces (02) 28.35

pounds (lb) 0.4536

short tons (ton) 0.9072

British thermal unit (BTU) 0.2520

grams

kilograms

metric tons

kilocalories

Fahrenheit degrees 0.5556(F" - 32) Celsius degrees

CONVERSION FACTORS

Metric to 1J.S. Customary

!LY To Obtain

0.03937 inches

0.3937 inches

3.281 feet

0.6214 miles

10.75 square feet

0.3861 square miles

2.471 acres

0.2642 gallons

35.31 cubic feet

0.0008110 acre-feet

0.00003527 ounces

0.03527 ounces

2.205 pounds

2205.0 pounds

1.102 short tons

3.968 British thermal units

1.8(C?) + 32 Fahrenheit degrees

U.S. Customary to Metric
ACKNOWLEDGMENTS

We thank Dr. Herbert Hidu, Professor of Zoology, Llniversity of Maine, for

reviwing the manuscript and offering many helpful suggestions.

vi
‘b

Figure 1. American oyster from Wellfleet Harbor, Massachusetts (Galtsoff 1964).

AMERICAN OYSTER

b NOMENCLATURE/TAXONOMY/RANGE

Scientific name . . . . . Crassostrea

virginica (Gmelin)

Preferred common name . . . American

oyster (Figure 1)

Other common name . . . Eastern oyster

Class . . . . . Bivalvia (Pelecypoda)

Order . . . . . . . . . . . Pteroidea

Family. . . . . . . . . . . Ostreidae

Geographic range : In estuaries,

drowned river mouths, and behind

barrier beaches along the east

coast of North America, from the

Gulf of St. Lawrence, Canada, to

Key Biscayne, Florida. In the

Gulf of Mexico to the Yucatan

Peninsula of Mexico, and in the

West Indies to Venezuela. Introduced to Japan, Australia, Great

Britain, Hawaii, and the west

coast of North America (Ahmed

1975). The largest American

oyster populations are in the

Gulf of Mexico, Chesapeake Bay,

and Long Island Sound.

MORPHOLOGY/IDENTIFICATION AIDS

The left valve is almost always

thicker and heavier than the right,

and more deeply cupped (Yonge 1960;

Galtsoff 1964). The oyster is cemented

to the substrate on its left valve.

Hinge teeth are absent, but a buttress

on the right valve fits into a depression on the left. There is no gap between the valves when fully closed.

Shell shape is variable. On hard

bottoms, beaks (umbones) usually are

curved and point toward the posterior,

whereas in silty environments or on

reefs, umbones are usually straight.

Single oysters from hard substrates

are rounded and ornamented with radial

ridges and foliated processes, whereas

those from soft substrates or reefs

are more slender and are sparsely ornamented. Shell thickness also depends

on environment. Oysters on hard substrates have thicker and less fragile

shells than those on soft substrate.

The index of shape (height + width/

1
length) varies from 0.5 to 1.3 in

southern populations and from 0.6 to

1.2 in northern populations.

Growth rings are oval with greatest growth along the dorsal-ventral

axis. The principal growth axis is not

permanent and may change several times

over the lifespan of an individual,

resulting in a zigzag pattern. The

growth axis may change as much as 90".

Oysters 3 to 5 years old are usually

10 to 15 cm in height. Although tissue

mass reaches an upper limit, the shell

continues to grow over the lifespan of

an oyster (Stenzel 1971). The largest

height reported in the North Atlantic

region is 35.5 cm, from the Damariscotta River, Maine (Galtsoff 1964).

The American oyster is isomyarian

(adductor muscles are equal in size).

The interior of the shell has a

purple-pigmented adductor muscle scar

situated slightly posterior and ventral. A second muscle scar, of the

quenstedt muscle, is situated under

the hinge. Chalky deposits may occur

on the inside of the shell. The adductor muscle scar pigmentation distinguishes the American oyster from

similar species. In C. rhizophorae and

C. gigas the muscle scar is lightly

pigmented, and in C. commercial is and

C. rivularis it 7s Gigmented. AlThough C. gigas has been introduced to

Salt Pond in Blue Hill, Maine, Wellfleet Harbor, Massachusetts, and

Mobile Bay, Alabama, the only significantly numerous sympatric Crassostrea

species is C. rhizophorae, which

occurs along tile southeastern and gulf

coasts. The shell of C. rhizophorae is

less plicated than that of C. virginica. Crassostrea species a6 distinmsha6le strea species by the

presence of a promyal chamber, which

is well developed in C. virginica.

Crassostrea are ovipar&, releasing

gametes into the water, whereas Ostrea

incubate fertilized eggs in the mantle

cavity. Advanced Crassostrea larvae

are distinguished from larvae of other

bivalves by length-width measurements,

and an asymmetric umbo. The dentition

on the hinge distinguishes larval C.

virginica from other Crassostrea. -

REASON FOR INCLUSION IN SERIES

American oysters support an important commercial fishery from the

Gulf of Mexico to the Gulf of St. Lawrence, and are an important mariculture species. More U.S. plants produce

oyster products than any other single

fishery product, and over 10,000 people are employed in the oyster industry. Oysters are valued as a luxury

food item. They are the keystone species of a reef biocoenosis that includes several hundred species (Wells

1961). Because oysters occur in estuarine areas, they are vulnerable to

disturbance by development projects.

LIFE HISTORY

Spawning

Gametogenesis and spawning are

stimulated by temperature (Hopkins et

al. 1954; Kaufman 1978; Andrews 1979).

The temperatures at which spawning

occurs differ among populations. Stauber (1950) recognized three physiological races, two from the east coast

and one from the gulf coast, which

spawn at 16.4'C, 2O.O"C, and 25.0°C,

respectively. Evidence for physiological races was given by Loosanoff

(1969), who found that gametes of 60%

of the oysters from Long Island Sound

populations ripened at 15°C after 45

days, whereas only 20% of the oysters

from a New Jersey population had ripe

gametes after 72 days at the same temperature. At 18°C none of the oysters

from south of New Jersey matured, even

after 3 years. The time required for

gonad maturation (D) in Long Island

Sound oysters is inversely proportional to temperature (T):

D = 4.8 + 4205 e

-0.3554T

3
Spawning may depend secondarily on

tidal cycle; sunlight warmed water

during low tide and stimulated spawning (Drinnan and Stallworthy 1979).

Spawning is initiated by one or

more males, which release their sperm

and a pheromone into the water. The

females spawn when sperm enter the

water transport system (Andrews 1979),

or when pheromone stimulates females

to release their eggs in a mass spawning (Bahr and Lanier 1981). Females

produce 23.2 to 85.8 million eggs per

spawning, with the number of eggs

proportional to the size of the individual (Davis and Chanley 1955). Fecundities of 15 million to 115 million

were cited by Yonge (1960). Females

may spawn several times in one season,

and the number of eggs produced is not

proportional to the spawning interval.

As spawning interval increases, obviously the number of eggs per season

decreases (Davis and Chanley 1955).

The spawning season is longer in warmer climates: from April to October in

the Gulf of Mexico (Hayes and Menzel

1981) ; but from July to August in

Malpeque Bay, Prince Edward Is1 and

(Kennedy and Battle 1963); and only in

July at Bideford River Estuary, Prince

Edward Island, Canada (Drinnan and

Stallworthy 1979). The egg stage ends

at 6 hr after fertilization at 24°C

(Loosanoff 1964).

Larvae

Oyster larvae are meroplanktonic,

remaining in the water column for 2 to

3 weeks following fertilization (Bahr

and Lanier 1981). During this period

the larvae pass through several stages

of development (Carriker and Palmer

1979). After the blastula (3.2 hr),

gastrula (4.5 hr), and trochophore (10

hr) stages (Parrish 1969), the larvae

secrete a straight-hinge shell and

develop a ring of locomotory cilia

called the velum. The swimming

trochophore stage is reached in 6-8 hr

(Andrews 1979). This prodissoconch I

or straight-hinge larva is about 75 urn

in diameter. This stage is followed by

3

prodissoconch II, which is characterized by pronounced umbones. These

larvae are vigorous swimmers with a

pair of pigmented eyes and an elongate

foot with a large byssal gland (Andrews 1979). These larvae are 0.30 mm

in diameter (Galtsoff 1964).

Carriker (1951) found that younger larvae stay in the water column

about 1.0 m below the surface. Older

larvae remain near the bottom in the

halocline of estuaries during flood

tide and rise nearer the surface during the ebb tide, although Andrews

(1979) questioned this finding. Haskin

(1964) demonstrated that gradually

rising salinities stimulate older larvae to swim and falling salinities

cause them to sink. Hidu and Haskin

(1978) observed spiral swimming during

constant salinity, and linear swimming

during gradually increasing salinity;

swimming velocity increased by a factor of three at salinity near

100% seawater. Upward swimming is at

nearly 1 cm/set (Andrews 1979). These

behavioral traits perhaps result in

selective tidal transport and allow

larvae to avoid being flushed from the

estuary. Larvae may even be transported up an estuary (Seliger et al.

1982).

Juveniles

The larvae at 2 to 3 weeks after

spawning seek a solid surface and commence a period of crawling in a circular area, presumably seeking a place

for attachment (Andrews 1979). After

attachment with a droplet of liquid

cement exuded from a pore in the foot,

they lose the velum and foot and are

now called spat. Shells are preferred

as attachment or setting sites, but

stones and other surfaces may be used.

Spat that set during the first 3 days

after metamorphosis may grow faster

than those setting later (Losee 1979).

Metamorphosis may be delayed if suitable substrate is not present (Newkirk

et al. 1977).
Several factors influence the

setting behavior of larvae. Hidu and

Haskin (1971) suggested that rising

temperature over tidal flats during

the flood tides stimulates setting. In

the laboratory, rising temperature

triggered setting (Lutz et al. 1970).

Swimming larvae have positive phototaxis, which becomes negative with

increased temperature (Bahr and Lanier

1981). More oysters settled in the

subtidal zone than elsewhere in

Delaware Bay (Hidu 1978). Setting was

greater on shells at 2 m depth than on

shells at 1.2 m or 0.3 m (Drinnan and

Stallsworthy 1979). However, Andrews

(1979) observed more setting off the

bottom, and attributed the opposite

results to siltation in shallower

water.

Oyster larvae set in established

oyster beds. Crisp (1967) postulated

that larvae are attracted to the proteinaceous surface of the periostracum

of adult shells and observed that larvae do not settle on shells that had

been treated with bleach. Hidu (1969)

demonstrated, however, that a waterborne factor, perhaps a pheromone, is

involved: larvae settle on oyster

shells associated with existing oysters. Currents also influence setting

patterns. Keck et al. (1973) found

that setting in estuaries is heaviest

on the eroding banks of tidal creeks.

Adult

Because adults are completely

sessile, their distribution depends on

where the larvae set and on subsequent

mortality. Oysters typically occur in

clumps called reefs or beds, in which

they are the dominant organism. The

mass of shells often results in alteration of currents and increased

deposition so that the local environment is modified.

Adults are dioecious, but often

change gender (Bahr and Lanier 1981).

The gender and the process of sex

inversion are genetically determined

by perhaps three loci (Haley 1977).

Typically the young adults are

predominately males; subsequent sex

inversion with age increases the

number of females. Sex ratios in the

James River Estuary, Virginia, change

from 90% males at 1 year of age to 80%

females in older oysters (Andrews

1979).

GROWTH CHARACTERISTICS

Growth is greatest during the

first 3 months, and spat reach 15 mm

in 9 months (Bahr 1976). In their second year, juveniles that were 11 to 14

mm on April 3 were 18 to 22 mm on May

7, 23 to 27 mm on June 5, and 26 to 32

mm on July 2 (Carriker et al. 1982).

Body weight increased from 0.23 g to

4.0 g during this 3-month period.

Monthly shell increment ranged from I

to 3 mm per month in South Carolina

(Manzi et al. 1977; Manzi and Burrell

1977); or 20 mm per year in Maine

(Price et al. 1975). Instantaneous

monthly growth coefficients ranged

from 0.42 to 0.84 (Gillmor 1982). The

marketable size of 90 mm is attained

in 3 to 5 years.

Growth is influenced by temperature, salinity, intertidal exposure,

turbidity, and food. Growth is greatest in August and September after

spawning, when glycogen reserves are

restored (Loosanoff and Nomejko 1949;

Price et al. 1975). Growth ceases during winter, except in Florida, where

growth was continuous throughout the

year (Butler 1952). Growth is slowed

by spawning because energy is used for

gamete production instead of production of body biomass. Butler (1953)

noted a weight increase after spawning

without an increase in length.

Fluctuating environments may promote better growth. Oysters in fluctuating salinity grow better than

those under constant conditions

(Pierce and Conover 1954). Oysters

exposed during the tidal cycle grow

about the same as those continuously

submerged (Gillmor 1982). Long expos4

4
ure, however, reduced growth; those

exposed 20% of the time grow twice as

fast as those exposed 60% of the time.

Growth rate is directly related to

phytoplankton density, and some of the

observed effects may be due to changes

in phytoplankton. Manzi et al. (1977)

observed that oysters grow faster in

salt ponds than in tidal creeks, where

primary productivity is lower. Crowding may prevent spawning and thus indirectly may lead to increased growth

(Butler 1953).

Oysters over 200 mm long are not

uncommon. A Walford plot of

intertidal oysters predicts that

oysters would cease growing at 140-mm

length (Dame 1971).

COMMERCIAL HARVEST

The American oyster had traditionally supported a significant industry along the entire eastern seaboard. Today, there are only six commercial areas in the North Atlantic

region (Figure 2). Domestic landings

have decreased from about 100 million

lb during the 1920's to 50 million lb

during the 1960's, and have not recovered to the original levels (Table 1)

(Matthiessen 1969). Although harvests

in the Gulf of Mexico and South Atlantic have remained stable for the past

30 years, harvests in the mid-Atlantic

and Chesapeake Bay have declined. In

Long Island Sound, persistent set

failure has been responsible for declining stocks. Although oysters spawn

at the summer temperatures of the

sound (20" to Zl"C), setting must

occur in warmer estuaries. Because of

shoreline development, the amount of

setting area has declined (Matthiessen

1969). Heavy mortalities due to the

predatory starfish Asterias forbesi

and the gastropod Urosalpinx cinerea

in saltwater, and the predatory flatworm Stylochus ellipticus in brackish

water, have also contributed to declining stocks (Matthiessen 1979).

Oysters are harvested in a

variety of ways, including handpicking

Of clumps from reefs (Bahr and Lanier

1981)) hand and patent tonging, and

dragging from sailpowered craft in the

Chesapeake Bay, and dredging from

POWerCraft in Long Island Sound and

(Korringa 1976).

The American oyster is also one

of the predominant species used in

mariculture, including in the North

Atlantic region. In 1980 the yield of

cultured oysters was 23,705,OOO lb

valued at $37,085,000. This represents 55% of the total harvest of

42,439,OOO lb. The equivalences between different values reported for

harvest are: 1 bu = 34 1 = 32 kg total

weight = 7.8 pints

weight (Pruder 1975).

= 3.4-kg meat

The market quality varies with

the season. The yield of meats is lowest in the summer months and peaks in

March (Rockwood and Mazek 1977). This

corresponds to a reduced-condition

index following spawning (Hopkins et

al. 1954; Lawrence and Scott 1982).

Population Dynamics

The enormous numbers of eggs and

larvae produced by American oysters

largely perish before setting. Following spawning, oyster larvae are common

in the plankton, with numbers reaching

5,000 to lO,OOO/kl in Canadian waters

(Drinnan and Stallworthy 1979) and

2,000 to 5,50O/kl in Virginia (Andrews

1979; Seliger et al. 1982), with a

peak in abundance after high tide

(Andrews 1979). The daily mortality of

larvae is 10% (Drinnan and Stallworthy

1979). Newly set spat had 79% to 99%

mortality in 1 month in Massachusetts

(Krantz and Chamberlin 1978). Spat

mortality of 50% to 70% in Delaware

Bay was reduced to 30% to 40% if spat

were protected from predators (Tweed

1973). Spat survival was less in dense

sets than in sparse sets in Chesapeake

Bay (Webster and Shaw 1968). Annual

changes in population density in Long
ATLANTIC OCEAN

MILES

0 5 0 1 0

0 5 0 100

KILOMETERS

l Commercial oyster areas

Figure 2. Recent commercial American oyster areas in the North Atlantic

Region. Commercial harvest is now prohibited in Great Bay and is low in

Pleasant Bay (Ralph Andrews, U.S. Fish and Wildlife Service, Newton Corner,

Massachusetts).

6
Table 1. Oyster harvests (thousands of pounds meat weight) by

geographical region for the years 1950-1980 (from various issues of

Current Fisheries Statistics, National Oceanic and Atmospheric

Administration).

k

Year New Englanda Mid-Atlantic Chesapeake

South Gulf of

Atlantic Mexico

1950

1951

1952

1953

1954

1955

1956

1957

1958

1959

1960

1961

1962

1963

1964

1965

1966

1967

1968

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

4727

1970

2209

1038

745

619

506

405

276

387

500

453

294

452

195

340

N/Ah

II

II

II

II

II

II

II

II .

II

II

II

II

II

II

18170

17410

16767

14462

13377

9848

8466

7981

4296

1392

1154

1921

2362

951

1356

757

N/AII

29954 3033 12292

29598 3783 11519

34418 4111 14637

36946 4019 12836

41587 3811 11443

39227 2260 13881

37064 3656 13513

34234 3069 14307

37530 2651 10408

33322 3516 13721

27111 4119 16098

27500 3984 18240

19939 3850 18838

18274 4837 24139

22098 3527 23385

21188 4082 19156

21232 3657 17182

25798 3160 21747

22679 2965 26739

22157 1830 19765

24668 1626 17714

25557 1846 20266

24066 1868 18260

25400 1656 14914

25021 1841 14878

22640 1585 19295

20964 1704 21569

17929 1847 18081

21531 2138 18212

20428 2441 15289

21906 N/A N/A

a Includes Connecticut and Rhode Island from the Mid-Atlantic Region.

b N/A = Data not available.

Island Sound (MacKenzie 1981) suggest 94% in an estuary (Manzi and Burrell

survival rates: spat occur at densi- 1977). Survival was 100% in areas

ties of 200 to 10,000/m2; l- to 2-year protected from wave action in North

olds at 300/m2; and 3- to 4-year-olds Carolina, and 50% per month if exposed

at 75/m2. Adult survival in South to waves (Ortega 1981).

Carolina was 85% in a salt pond and

7
ECOLOGICAL ROLE

Larvae feed on plankton. Guillard

(1957) observed that small, naked

flagellates (chrysophytes) are the

preferred food for larvae. Davis and

Calabrese (1964) found that at low

temperatures larval growth is best

with a diet of naked flagellates:

whereas at temperatures above 27°C

naked algae do not survive and chlorophytes are a better food source. Larvae in turn serve as food for a wide

variety of filter feeders (Andrews

1979).

The adults are important filter

feeders in estuarine ecosystems and

feed on naked flagellates in the 3- to

4-pm size range (Haven and MoralesAlamo 1970). For each gram of dry

weight of tissue, an oyster filters

1.5 l/hr, with a maximum of 1.9 l/hr

(Palmer 1980). The filteration rate is

independent of the algal food concentration in the seawater.

Oysters are the keystone species

of a diverse community in the estuarine ecosystem. Bahr and Lanier

(1981) reported the occurrence of 42

macrofaunal species or groups, and

Wells (1961) listed 303 species

associated with the oyster community.

Because of their abundance, oysters

are responsible for 87.5% of the respiration of an oyster reef (Bahr and

Lanier 1981).

Oysters are subjected to a variety of diseases and parasites and support several predator populations

(Galtsoff 1964). Bacterial diseases

include Vibrio and Pseudomonas species. The fungus Dermocystidium

marinum infects oysters in the southern range from Delaware to Mexico. The

haplosporidian protozoan Minchinia

nelsoni is responsible for the disease

-(multinucleate spheroid unknown),

and Minchinia costalis for SSO (seaside- organism).hinia nelsoni, ’

found from North Carolina to Massachusetts (Krantz et al. 1972), caused

extensive oyster mortalities in the

Delaware Bay in 1957 and in Chesapeake

Bay in 1960 (Andrews 1968). Minchinia

costalis caused extensive mortalities

in the seaside bays of the Delmarva

Peninsula in 1960 (Rosenfield 1971).

Oyster predators include the

gastropod oyster drills (Urosalpinx

cinerea and Eupleura caudata), the

whe7k(Busycon canali-), the

starfish'wias forbesi) and the

crabs (Cancer irroratus. Cillinectes

and Carcinus maenus)(G

*-ill oysters are suscept4~~5"Z

predation by-oyster drills, which bore

through the shells with a combination

of chemical dissolution of the shell

and drilling; but only smaller oysters

are susceptible to predation by crabs

and starfish. Widespread infestation

also occurs from the boring sponge

Cliona, which lowers quality. Oyster

reefsmay be smothered by excreta of

worms of the genus Polydora. Juveniles

are preyed upon by the flatworm Stylothus ellipticus (MacKenzie 1970).

Major competitors of the oyster

include the slipper limpets (Cre idula

sp.) and the jingle shells-7&o-Z

sp.) as well as barnacles and other

oysters that set on adult shells (MacKenzie 1970). The mussel (Brachiodontes exustus) may also compete with

oystemega 1981).

ENVIRONMENTAL REQUIREMENTS

The American oyster typically

lives in shallow, well-mixed estuaries, lagoons, and oceanic bays that

fluctuate widely from hot to cold temperatures, low to high salinities, and

clear to muddy waters (Andrews 1979).

Because they live in such an extremely

varied habitat, exact environmental

requirements alone or in combination

are difficult to define.

Temoerature

Larvae do not tolerate as wide a

range of temperatures as adults. Water

temperatures of 30' to 34°C impair

8
growth, and even a brief exposure for

10 min at 40°C retards growth in

Cheasepeake Bay (Hidu et al. 1974).

The temperatures cited for fastest

growth and highest survival, 27.5" to

32.5'C, in Long Island Sound (Davis

and Calabrese 1964), seem a bit high.

Adults tolerate a water temperature range from -1.7"C in New England

to 36°C in the Gulf of Mexico. Oysters

may be exposed at low tide to temperatures below freezing or above 49'C

(Galtsoff 1964). High temperatures

increase the mortality rate; temperatures above 35°C for the whole tidal

cycle caused death of some oysters

(Tinsman and Maurer 1974). The critical thermal maxima for the American

oyster is 48.5"C (Henderson 1929).

Oysters tolerate freezing of their

tissues, and revive after thawing

(Loosanoff 1965a).

Optimum temperatures for adult

American oysters are 20" to 30°C. Optimum temperatures for pumping were

20" to 25°C (Collier 1951). Growth

ceased below about 8°C (Price et al.

1975). Oysters at 2" to 7°C remained

inactive. Exposure to warm temperatures out of season stimulated growth

if food was available (Ruddy et al.

1975). Growth is possible between 6'

and 32°C with the optimum at 25“ to

26°C (Galtsoff 1964). Exposure to 35°C

water accelerated gametogenesis and

spawning, but subsequent spawning was

prevented (Quick 1971).

Differences in thermal requirements of oysters from different areas

have led to the postulation of different races, each with different temperature requirements (Ahmed 1975).

Spawning temperatures for three distinct races were reported by Stauber

(1950) to be 16.4"C for the northern

race (New England), 2O.O"C for the

mid-Atlantic race, and 25.0°C for the

Gulf of Mexico race. Additional evidence for the existence of physiological races was reported by Menzel

(I955), who found that ciliary activity continued at 0°C in northern

oysters but ceased at 6°C in southern

oysters. Andrews (1979) believes there

are other races as well. Genetic studies did not closely support the existence of physiological races. Buroker

et al. (1979) found that all oysters

studied were identical, except oysters

from Nova Scotia and Florida. These

populations were 82% similar, about

the level of similarity between C.

virginica and C. rhizo horae

can successfully hybridize --??-$h:h~

Lanier 1981). Oysters in Laguna Madre,

Texas, however, are genetically distinct from four other gulf populations

(Groue and Lester 1982). Measurement

of isozymes in the genetic studies,

however, may not indicate these races.

Salinities

Salinities above 7.5 ppt are required for spawning (Loosanoff 1948).

Larvae tolerate salinities of 3.1 to

30.6 ppt (Carriker 1951), but grow

fastest and survive best at salinities

above 12.5 ppt (Davis and Calabrese

1964). Most larvae in a New Jersey

estuary were in the halocline at

salinities above 5 ppt (Carriker

1951). Optimum salinities for the

growth of spat were 15 to 22 ppt

(Chanley 1957).

Adult oysters tolerate a salinity

range of 5 to 30 ppt, outside of which

they discontinue feeding and reproducing. The optimum salinity range is 10

to 28 ppt (Loosanoff 1965a). Loosanoff

(1965b) found that many oysters survive 3 ppt for 30 days. Large mortalities, however, have been associated

with prolonged spring floods in the

James River, Virginia (Andrews et al.

1959); in Mobile Bay, Alabama (May

1972); and in the Santee River, South

Carolina (Burrell 1977). Salinities

during these freshets were below 2

ppt. Oysters in Louisiana died after

14 days at 6 ppt (Anderson and

Anderson 1975).

Low salinity inhibits gonadal

maturation in oysters in Chesapeake

Bay (Butler 1949) and Long Island

9
Sound (Loosanoff 1953). Reproductive

failure may be a direct effect of salinity or might be caused by inadequate feeding at low salinity. Lowered

salinity may benefit oyster populations by killing predators. Oyster

drills and starfish cannot tole

brackish water (Loosanoff 1965a).

Habitat

Oysters can grow equally we1

. -

on

rocky bottoms or on mud Capable of

supporting their weight. Soft muddy

substrates may be improved by adding

clam or oyster shells. Oysters from

muddy substrates are more slender than

those from hard substrates (Galtsoff

1964). Hidu (1978) found that oysters

prefer to set on the bottom rather

than on panels suspended in the water

column, and are generally found subtidally in Delaware Bay. The preferred

habitats in shallow estuarine waters

include flats and offshore bars (Hidu

1968) and oyster reefs (Bahr and Lanier 1981). Maximum setting occurs on

horizontal surfaces (Clime 1976).

ate

Currents are important to American oysters. The volume of water immediately above an oyster bed must be

renewed 72 times every 24 hr for maximum feeding; therefore, oysters require a moderate current (Galtsoff

1964). Tidal flows of 156 to 260

cm/set or higher are needed for optimum growth (Veal et al. 1972). Turbulent currents, however, can damage

shells from transported sand and pebbles (Galtsoff 1964). Although a

velocity of 150 cm/set caused unattached oysters to tumble along the

bottom (MacKenzie 1981). They are

found in greatest abundance in areas

of scour where current keeps the beds

free of sediment (Keck et al. 1973).

Currents are also necessary for

removal of silt and feces.

Distribution is strongly correlated with mean low tide (MLT)

elevation in Great Bay, New Hampshire

,(Hardwick-Witman and Matthiesson

1983). There were 5.6/m2 at 0 m MLT

elevation, 2.0/m2 at 0.5 m, 0.4/m2 at

1 m, and none at 1.5 m.

Other Environmental Factors

Hourly oxygen consumption is 39

ml/kg for a whole animal or 303 ml/kg

of wet tissue (Hammen 1969). Oxygen

consumption increases with increasing

temperature; Qlo values (the factor by

which a reaction velocity is increased

by a rise in temperature of 1OY) reported by Bass (1977) range from 1.2

to 2.3 for gill and 2.7 to 4.2 for

mantle tissue. There is a strong interaction between temperature and

salinity; oxygen consumption increases

much more at high temperatures if the

salinity is ;ower'(Figure 3). Oysters

are facultative anaerobes and are able

to survive daily exposure. They can

also survive anaerobically for 3 days

following spawning (Galtsoff 1964).

Oxygen consumption is zero with the

valves closed (Hammen 1969).

Oysters are able to tolerate

turbid water, but pumping rate decreases with increasing turbidity.

Pumping rate can be reduced 70%-85%

over the range 0 to 1 g/l, depending

on the nature of the suspended sediment (Loosanoff and Tommers 1948). In

natural environments, however, oysters

grow better in the more turbid zones

in oyster beds than in less turbid

areas (Rhoades 1973).

Figure 3. Oxygen consumption in American oyster as a function of salinity

and temperature (Shumway 1982).

IO
LITERATURE CITED

Q

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:aenpdv:*

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16
50272 -101

REPORT DOCUMENTATION l:*EPORT No. 2. 3. Rec,p,ent’s Access,on No.

.~

4

PAGE FWS/OBS-82/II.23* ~___._. -L---_

,. Title and Subtitle 5. Report Date

Species Profiles: Life Histories and Environmental July 1984

Requirements of Coastal Fishes and Invertebrates (North 6.

Atlantic) -- American Oyster ~ ._~

'. Author(s) 8. Performing Organiratlon Rept. No

Mark A. Se1 lers and Jon G. Stanley_.____ __~ ~~~_ _~. ~~ _

3. Perform,“6 Organizatgon Name and Address 10. ProlectlTasklWork “n&t No.

Program in Oceanography Maine Cooperative Fishery Research

University of Maine at Unit 11. Contract(C) or Grant(G) No.

Orono 313 Murray Hall (C>

Ira C. Darling Center University of Maine

Walpole, ME 04573 Drone, ME 04469 (G)

_~_~

12. Sponsoring Organ~zaticn Name and Address 13. Type of Report 8. Period Covered

National Coastal Ecosystems Team U.S. Army Corps of Engineers

Fish and Wildlife Service

U.S. Dept. of the Interior

Waterways Experiment Statia,n __

P.O. Box 631 i 14.

Washington, DC 20240 Vicksburg, MS 39180 !

15. Supplementary Notes

*U.S. Army Corps of Engineers report No. TR EL-82-4

16. Abstract (Limit: 200 words)

--.- -

Species profiles are literature summaries of the taxonomy, morphology, range, life

history, and environmental requirements of coastal aquatic species. They are designee

to assist in environmental impact assessment. The American oyster, Crassostrea

virginica, is an important commercial and mariculture species. Spawning occurs

repeatedly during warmer months with millions of eggs released. Embryos and larvae

are carried by currents throughout the estuaries and oceanic bays where they occur.

The few surviving larvae cement themselves to a solid object, where they remain for tt

remainder of life. Unable to move, they must tolerate changes in the environment thal

range from -1.70 to 49oC, 5 to 30 ppt salinity, and clear or muddy water.

17. Document Analysis a. Descriptors

Estuaries

Oysters

Growth

Feeding

b. Identiflers/Open.Ended Te:ms

American oyster

Crassostrea virginica

Salinity requirements

Temperature requirements

c C&paWfl&l$%ro”p

18. Ldailzb~l,!, Sta!eme”t

Species profiles : 25168

Sei iers,‘hark A, Qii55 ,163 no.82

*

x

+

0

b l

Southern 5~~~~~ll~~~lliliillil Ii! Iii/

Kesearch Library

U.S. Department of the Interior

National Biological Service

Southern Science Center

700 Cajundome Blvd.

Lafayette, LA 70506-3 152

headquarters, Divwx of Biological

Services, Washington. DC

pastern Energy and Land Use Team

Leetown, WV

National Coastal Ecosystems Team

Strdell. LA

Western Energy and Land Use Team

Ft Collins. CO

Locations of Regv3nal Offices

REGION 1

Regional Director

U.S. Fish and Wildlife Service

Lloyd Five Hundred Building, Suite 1692

500 N.E. Multnomah Street

Portland, Oregon 97232

REGION 4

Regional Director

U.S. Fish and Wildlife Service

Richard B. Russell Building

75 Spring Street, SW.

Atlanta, Georgia 30303

REGION 2 REGION 3

Regional Director Regional Director

U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service

P.O. Box 1306 Federal Building, Fort Snelling

Albuquerque, New Mexico 87 I03 Twin Cities, Minnesota 55 I 11

REGION 5

Regional Director

U.S. Fish and Wildlife Service

One Gateway Center

Newton Corner, Massachusetts 02 I58

REGION 6

Regional Director

U.S. Fish and Wildlife Service

P.O. Box 25486

Denver Federal Center

Denver, Colorado 80225

REGION 7

Regional Director

U.S. Fish and Wildlife Service

101 I E. Tudor Road

Anchorage, Alaska 99503
DEPARTMENT OF THE INTERIOR

U.S. FISH AND WILDLIFE SERVICE

As the Nation’s principal conservation agency, the Department of the Interior has responsibility for most of our nationally owned public lands and natural resources. This includes

fostering the wisest use of our land and water resources, protecting our fish and wildlife,

preserving theenvironmental and cultural values of our national parks and historical places,

and providing for the enjoyment of life through outdoor recreation. The Department assesses our energy and mineral resources and works to assure that their development is in

the best interests of all our people. The Department also has a major responsibility for

American Indian reservation communities and for people who live in island territories under

U.S. administration.