REFERENCECOPY 

Do Not Remove from the Library 

U. S. Fish and Wildlife Service 

Biological Report 82 (I 1.65) 700 Cajun Dome Boulevard TR EL.s~-4 

July 1986 La foyette, Louisiana 70506 

Species Profiles: Life Histories and 

Environmental Requirements of Coastal Fishes 

and Invertebrates (Mid-Atlantic) 

AMERICAN OYSTER 

Coastal Ecology Group 

Fish and Wildlife Service Waterways ~xperiment station 

U.S. Department of the Interior U.S. Army Corps of Engineers 
Biological Report 82 (11.65) 

TR EL-82-4 

July 1986 

Species Prof i les: Life Histories and Envi ronmental Requi rements 

of Coastal Fishes and Invertebrates (Mid-Atlantic) 

AMERICAN OYSTER 

Jon G. Stanley 

Maine Cooperati ve Fishery Research Unit 

313 Murray Hall 

University of Maine 

Orono, ME 04469 

and 

Mark A. Sell ers 

Program in Oceanography 

University of Maine at Orono 

Ira C. Darling Center 

Walpole, ME 04573 

Project Manager 

Larry Shanks 

Project Off i cer 

John Parsons 

National Wetlands Research Center 

U.S. Fish and Wildlife Service 

1010 Gause Boulevard 

Slidell, LA 70458 

Performed for 

U.S. Army Corps of Engineers 

Coastal Ecology Group 

Waterways Experiment Station 

Vicksburg, MS 39180 

and 

National Wetlands Research Center 

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. Biol. Rep. 82(11). U.S. Army Corps of Engineers, TR EL-82-4. 

This profile should be cited as follows: 

Stanley, J.G., and M.A. Sellers. 1986. Species profiles: life histories and 

environmental requirements of coastal fishes and invertebrates (MidAtlantic)--American oyster. U. S. Fish Wildl. Serv. Biol. Rep. 82(11.65 ). U.S. 

Army Corps of Engineers, TR EL-82-4. 25 pp. 
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 

profi 1 e has sections on taxonomy, 1 ife hi story, 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 one of 

the foll owing addresses. 

Information Transfer Special ist 

National Wet1 ands Research Center 

U.S. Fish and Wildlife Service 

NASA-Sl i dell Computer Compl ex 

1010 Gause Boulevard 

Slidell, LA 70458 

U. S. Army Engineer Waterways Experiment Station 

Attention: WESER-C 

Post Office Box 631 

Vicksburg, MS 39180 
CONVERSION TABLE 

Metric to U.S. Custanary 

mil 1 iineters (mm) 

centimeters ( n) 

meters (m) 

ki 1 ometers ( km) 

2 

square meters (m ) 10.76 

square ki 1 ometers ( km2) 0.3861 

hectares (ha) 2.471 

liters (1) 

cubic neters (m3) 

cubic meters 

To Obtain 

inches 

inches 

feet 

mi 1 es 

square feet 

square 'nil es 

acres 

gal 1 ons 

cubic feet 

acre-feet 

mil 1 igrams (mg) 0.00003527 ounces 

gralils (g) 0.03527 ounces 

kil ograms (kg) 2.205 pounds 

metric tons ( t) 2205.0 pounds 

metric tons 1.102 short tons 

ki 1 ocal ories ( kcal ) 3.965 British thennal units 

Cel s ius dey rees 1.8(OC) + 32 Fahrenheit degrees 

U.S. Customary to Metric 

inches 25.40 

inches 2.54 

feet (ft) 0.3048 

fa thoms 1.829 

miles (mi) 1.609 

nautical miles (mi) 1.852 

square feet (ft2) 

acres 2 square miles (mi 

gal 1 ons ( gal ) 

cubic feet (ft3) 

acre-feet 

ounces (02) 28.35 

pounds (lb) 0.4536 

short tons (ton) 0.9072 

British thermal units (Btu) 0.2520 

mil 1 imeters 

centimeters 

ineters 

meters 

kilometers 

ki 1 o~eters 

square meters 

hectares 

square kilometers 

1 i ters 

cubic meters 

cubic meters 

grains 

kilograms 

metric tons 

ki 1 ocal ories 

Fahrenheit degrees 0.5556(OF - 32) Celsius degrees 
CONTENTS 

Page 

PREFACE ................................. CONVERSIONTABLE ............................ ACKNOWLEDGMENTS ............................. 

NONMENCLATllRE /TAXONOMY /RANGE ...................... MORPHOLOGY/IDENTIFICATION AIDS ..................... REASON FOR INCLUSION ON SERIES ..................... LIFE HISTORY .............................. Larvae ................................. Juveniles ............................... Adults ................................ GROWTH CHARACTERISTICS ......................... COMMERCIAL SHELLFISHERIES ........................ Popu 1 at i on Dynamics .......................... ECOLOGICALROLE ............................. ENVIRONMENTAL REQUIREMENTS ....................... Temperature .............................. Salinity ............................... Substrate and Current ........................ Oxygen ................................ Turbidity and Sedimentation ...................... Acidity ................................ 

LITERATURECITED ............................ 
ACKNOWLEDGMENTS 

We thank Herbert Hidu, Professor of Zoology, University of Maine; Edwin W. 

Cake, Jr. , Head, Oyster Biology Section, Gulf Coast Research Laboratory; Mark 

Chatry, Marine Biological Laboratory, Louisiana Department of Wi 1 dl ife and 

Fisheries; and Dexter S. Haven, Virginia Institute of Marine Science, for 

reviewing the manuscript and offering many helpful suggestions. 
Figure 1. American oyster (Galtsoff 1964). 

AMER ICAN OYSTER 

Scientific name . . . . . Crassostrea 

vi r g i n i ca (Gmel in) 

Preferred common name . . . American 

oyster (Figure 1) 

Other common name . . . Eastern oyster 

Class . . . . . Bivalvia (Pelecypoda) 

Order . . . . . .Mytiloida (Pteroidea) 

Fami ly . . . . . . . . . . . 0s trei dae 

Geographic range: The American oyster 

lives in estuaries and behind 

barrier islands along the east 

coast of North America, from the 

Gulf of St. Lawrence, Canada, to 

Key Biscayne, Florida. Its range 

extends to the Yucatan Peninsula 

of Mexico and the West Indies to 

Venezuela. This species was 

successfully introduced in Japan, 

Australia, Great Britain, Hawaii, 

and the west coast of North 

America (Ahmed 1975). In the 

mid-Atlantic region, the American 

oyster is most abundant in Long 

Island Sound, Delaware Bay, and 

Chesapeake Bay. 

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 fu1 ly 

closed. 

Shell shape is variable. On hard 

bottoms, beaks (umbones) usual ly 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 (Figure 

I), whereas those from soft substrates 

or reefs are more slender and are 

sparsely ornamented. She1 1 thickness 

a1 so depends on envi ronment . Oysters 

on hard substrates have thicker and 

less fragile shells than those on soft 

substrate. The index of shape (height 

+ width/length) varies from 0.5 to 1.3 
in southern populations and from 0.6 

to 1.2 in northern populations. 

The shell grows along a 

dorsal-ventral axis, but the angle of 

the axis is not permanent and may 

change several times during the 

lifespan of an individual, resulting 

in a zigzag pattern. The growth axis 

may change as much as 90 degrees. The 

shell is usually 10 to 15 cm long when 

the oyster is 3 to 5 years old. 

Although tissue mass reaches an upper 

limit, the shell continues to grow, 

primarily in thickness, over the 

lifespan of the oyster (Stenzel 1971). 

The American oyster is monomyarian (anterior adductor muscle has 

been lost). The interior of the shell 

has a purple-pi gmented adductor muscle 

scar situated slightly posterior and 

ventral. A second muscle scar, of the 

Quenstedt's muscle, is situated 

ventral to and a short distance from 

the hinge. The purple pigmentation on 

the adductor muscle scar distinguishes 

the American oyster from similar 

species. In the mangrove oyster (5. 

rhizo horae) and Pacific oyster (C. & t e muscle scar is 1 i ghtiy 

pigmented and in C. rivularis it is 

unpigmented. Tre shell of the 

mangrove oyster is less plicated than 

that of the American oyster. There 

are no other species of Crassostrea 

sympatric with the American oyster in 

the Mid-At lant ic region. Species of 

Crassostrea are diytinguishab'le f rom 

species of Ostrea species by the promyal chamber, which is well developed 

in Crassostrea species, but not in 

Ostrea. By trapping salt water, this 

chamber may allow the American oyster 

to tolerate wider fluctuations in 

salinity in estuaries. 

Crassost rea species are oviparous 

(gametes are released into the water), 

whereas Ost rea species incubate 

fertilized eggs in the mantle cavity. 

Advanced larvae of American oysters 

are distinguished from the larvae of 

other bivalves by length-width 

measurements and an asymmetric umbo. 

The dentition on the hinge of the 

larvae of the American oyster is 

distinctly different from that in 

other bi val ves (Lutz et a1 . 1982). 

REASON FOR INCLUSION IN SERIES 

The American oyster supports an 

important commercial fishery from the 

Gulf of St. Lawrence to the Gulf of 

Mexico, and is an important mariculture species. More oysters are 

processed than any other single 

fishery product in the United States, 

and over 10,000 people work in the 

oyster industry. Oysters are valued 

as a luxury food item. The American 

oyster is the keystone species of a 

reef biocoenosis that includes several 

hundred species (We1 1s 1961). Because 

the oyster inhabits estuaries, it is 

particularly vul herable to urban and 

industrial disturbances. 

LIFE HISTORY 

Gametogenesis and spawning are 

stimulated by changes in water temperature (Kaufman 1978; Andrews 

1979a, 1979b; Kennedy and Krantz 

1982b). Spawning temperatures differ 

among populations. Based on spawning 

temperature, Stauber (1950) recognized 

three phys i 01 ogi cal races, one from 

the Gulf of Mexico that spawns when 

water temperatures are near 25 OC, and 

two from the east coast that spawn at 

16 OC and 20 OC. Evidence for 

physiological races also was reported 

by Loosanoff (1969), who found that 

gametes of 60% of the oysters from 

Long Island Sound populations ripened 

at a water temperature of 15 OC 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 OC none of 

the oysters south of New Jersey 

matured in a holding pond in 

Connecticut, even after 3 years. In 

Barnegat Bay, New Jersey, oysters 

first spawn when water temperature 

reaches 20 OC, but subsequent spawning 
requires water temperatures of at 

least 22 "C (Nelson 1928). In Delaware, native oysters matured in 150 

days at 15 "C (Price and Maurer 1971), 

which is a much longer time than that 

reported by Loosanoff (1969). The 

days required for gonad maturation (D) 

in Long Island Sound oysters are 

inversely proportional to temperature 

(T in "C): 

Delaware oysters require six times as 

long to ripen at water temperatures 

from 12 to 20 OC as do Long Island 

Sound oysters (Price and Maurer 1971). 

In Chesapeake Bay, spawning occurs 

when water temperatures are 21 to 24 

"C, with limited spawning at 15 to 20 

"C (Kennedy and Krantz 1982). 

The variation in spawning 

temperature may be caused by other 

factors. Kennedy and Krantz (1982) 

postulated that phytoplankton blooms 

and nutrition may be responsible for 

stimulating spawning in Chesapeake Bay 

oysters. 

The time and intensity of 

spawning do not depend directly on 

tidal cycles (Loosanoff and Nomejko 

1951). During low tide, however, the 

sunlight may warm the water and 

stimulate spawning (Drinnan and 

Stal lworthy 1979). 

Spawning is initiated by one or 

more males that release their sperm 

and a pheromone into the water. The 

females spawn when sperm enter the 

water transport system (Andrews 

1979a), or when pheromone stimulates 

females to release their eggs in a 

mass spawning (Bahr and Lanie.r 1981). 

Each female produces 23 mil lion to 86 

million eggs per spawning; the number 

is proportional to the size of the 

individual (Davis and Chanley 1955). 

Individual fecundities of 15 million 

to 115 million were cited by Yonge 

(1960). Females may spawn several 

times in one season; as the interval 

between spawnings increases, the 

number of eggs produced per season 

decreases (Davis and Chanley 1955). 

The quantity of sperm produced depends 

on the quantity of stored glycogen of 

the male oyster at the beginning of 

the spawning season (Loosanoff and 

Davis 1952). 

The spawning season is longer in 

warmer climates: from Apri 1 to October 

in the Gulf of Mexico (Hayes and Menzel 1981); but only in July near 

Prince Edward Island, Canada (Dri nnan 

and Stallworthy 1979). In Long Island 

Sound, spawning begins around July 1 

and lasts into August (Loosanoff and 

Nomejko 1951). In Chesapeake Bay, 

Maryland, spawning is from May to 

September; oysters in shal lower water 

spawn first (Beaven 1955). Oysters 

at an unusual depth of 40 m in cooler 

waters of Patuxent River estuary do 

not release a1 1 thei r gametes during 

the spawning season (Merri 11 and Boss 

1966). Kennedy and Krantz (1982) 

documented the spawning season for 18 

beds in Chesapeake Bay. Spawning 

begins in May in some beds, and June 

in others. Spawning continues into 

August in most beds and into September 

in a few (to December in one bed). 

The spawning season in eastern shore 

bars extended over a longer period 

during the early 1960s than in 1977 to 

1978. In the James River estuary, 

Virginia, spawning commences in late 

May and continues unti 1 October 

(Loosanoff 1932). The eggs hatch 

about 6 hours after fertilization at 

water temperatures near 24 "C 

(Loosanoff 1965a). 

Larvae 

Oyster larvae are meroplanktoni c 

and remain in the water column for 2 

to 3 weeks after hatching (Bahr and 

Lanier 1981). In Milford Harbor, 

Connecticut, the larval period is 13 

to 16 days at 22 "C (Prytherch 1929). 

During the planktonic phase, the 

larvae pass through several stages of 

development ( C a r r i k e r and Palmer 

1979). After the blastula (3.2 hr), 
gastrula (4.5 hr), and trochophore (10 

hr) stages (Parrish 1969), the larva 

secretes a strai ght-hi nge shel 1 and 

develops a ring of locomotory cilia 

called the velum. This prodissoconch 

I larva (also termed straight-hinge 

larva or veliger) is about 75 urn in 

diameter. It develops into the prodissoconch I1 larva (also termed eyed 

larva or pediveliger), which is characterized by pronounced umbones. This 

larva is a vigorous swimmer, and has a 

pair of pigmented eyes and an elongated foot with a large byssal gland 

(Andrews 1979a). The prodi ssoconch 

larva is about 0.3 mm in diameter 

(Galtsoff 1964). 

Young larvae (prodissoconch I) in 

Little Egg Harbor, New Jersey, stay in 

the water column about 1.0 m below the 

surface (Carriker 1951). Older 1 arvae 

(prodissoconch 11) are near the bottom 

in the halocli ne of estuaries during 

flood tide and rise nearer the surface 

during the ebb tide. The late stage 

larvae congregate near the bottom of 

Delaware Bay during slack tide and are 

distributed throughout the water 

column during flood tide (Kunkle 

1957). Andrews (1979a) doubted the 

validity of these findings. In the 

laboratory, older larvae are stimulated to swim by increased salinities 

and inhibited by decreased salinities 

(Haskin 1964). Larvae are on the bottom of Milford Harbor, Connecticut, 

when the current is greater than 0.6 

m/sec and drop to the bottom in 

holding tanks at velocities of 0.3 to 

0.5 m/sec (Prytherch 1929). Swimming 

velocity increases by threefold at a 

salinity near 100% seawater (Hidu and 

Haskin 1978). Upward swimming is at 

about 1 cm/sec (Wood and Hargis 1971; 

Andrews 1979a). These behavioral 

traits may result in selective tidal 

transport so that larvae avoid being 

flushed from the estuary. Generally, 

larvae are transported toward the head 

of an estuary against a net downstream 

flow (Seliger et al. 1982) by using 

these behavioral responses. 

-- Juveni les 

Two to three weeks after 

spawning, oyster larvae seek a solid 

surface for attachment (called a set, 

or the process of setting) and commence crawl i ng in ci rcl es (Andrews 

1979a). In Long Island Sound, the 

first set is 18 days after the first 

spawning (Loosanoff and Nomejko 1951). 

After attachment with a droplet of 

1 iquid cement exuded from a pore in 

the foot, they lose the velum and foot 

and are now called spat (newly 

attached oysters). Shells are 

preferred as attachment, but stones 

and other firm 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 located (Newki rk 

et al. 1977). Burke (1983) defined 

settlement as the behavior of dropping 

to the bottom, in contrast to metamorphosis, which is the irreversible 

developmental process. 

Several factors influence the 

setting behavior of larvae. Hidu and 

Haskin (1971) suggested that rising 

tenperatu res over tidal flats duri ng 

flood tides stimulate setting. In the 

1 aboratory , rising temperature 

triggered setting (Lutz et a1 . 1970). 

Swimming larvae have positive phototaxis, which becomes negative with an 

increase in temperature (Bahr and 

Lanier 1981). Light inhi bits setting 

in holding tanks (Shaw et al. 1970) 

and oysters prefer to set on the 

undersides of shells (Ritchie and 

Menzel 1969). More oysters settle in 

the subtidal zone than elsewhere in 

Delaware Bay (Hidu 1978). 

Oyster larvae usually set in 

established oyster beds or where shell 

substrate is present. Crisp (1967) 

postulated that 1 arvae are attracted 

to the proteinaceous surface of the 

periostracum of adult shel 1s and 

observed that larvae did not settle on 
shells that had been treated with 

bleach. Hidu (1969) demonstrated, 

however, that a waterborne factor, 

perhaps a pheromone, stimulates larvae 

to settle on oyster shells. Currents 

also influence setting patterns: 

settlement in Delaware Bay is heaviest 

where tidal currents cut through salt 

marshes (Keck et al. 1973). Although 

high salinities stimulate settlement, 

mortality increases because oyster 

predators are more numerous at high 

salinities (Ulanowicz et a1 . 1980). 

Howeverythe number of adult spawners 

is not correlated with the density of 

spat produced (MacKenzie 1983). 

Reduction in the quantity of fresh 

shells and widespread siltation limits 

the habitat suitable for setting in 

most oyster beds in the mid-Atlantic 

region (MacKenzie 1983). 

The time of settlement varies 

among locations and is generally 

shorter than that of spawning. In the 

Niantic River estuary, Connecticut, 

most larvae settled in July and a few 

in August (Marshall 1959). In Long 

Island Sound, settlement is from 

mid-July to early August and again 

from late August through September 

(Loosanoff 1966). Large numbers of 

larvae sometimes die in mid-summer, 

perhaps because of blooms of 

dinof lagel lates. In Delaware Bay, 

larvae settle from around July 4 to 

early September (Maurer et al. 1971). 

Peaks in setting in the five 

tributaries studied occurred mostly in 

July. In Chesapeake Bay, Maryland, 

setting is from May to October with a 

two-week peak, usually in July (Beaven 

1955). Different tributaries in 

Chesapeake Bay have peaks at different 

times: July in the St. Mary's River, 

Island Bar and Holland Straits; July, 

August and September in bars in the 

open bay; August and September at 

Wreck Shoal; and July and September at 

Yorktown Fish Pier and Page's Rock 

(Andrews 1951). In the James River 

estuary, Virginia, settlement was from 

mid-June to mid-October with peaks in 

mi d-August and mid-September (Loosanoff 1932). 

Adu 1 ts 

Because adult oysters are 

sessi ley their distribution depends on 

where the larvae set and on subsequent 

survival of the spat. Oysters typically live in clumps called reefs or 

beds, in which they are the dominant 

organisms. The mass of shells sometimes alters the currents, and 

increases deposition of particulates 

so that the local environment is modified. 

Adults are often dioecious, but 

also often change gender as 

protandrous hermaphrodites (Bahr and 

Lanier 1981). The gender and the 

process of sex inversion are geneti - 

cally 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 1979a). 

GROWTH CHARACTERISTICS 

Oysters grow fastest during their 

first 3 months of life (Bahr 1976). 

In their second year, juveniles in 

Delaware Bay that were 11 to 14 mm 

long 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). Whole body weight increased 

from 0.23 g to 4.0 g in those months. 

In a review of growth rates in the 

American oyster, Ingle and Dawson 

(1952) cited the following sizes at 

corresponding age: 35 to 75 mm in 6 

mo and 100 to 125 mm at 4 years in 

Long Island Sound; 95 to 106 mm at 1 

year in New Jersey; 21 mm at 44 days, 

40 mn at 12 mo, and 90 mm at 23 mo in 

Chesapeake Bay. Oysters in the deep 

cool waters of Chesapeake Bay grow 

slower than those in shallow warmer 

waters (Merrill and Boss 1966). In 

the Virginia part of Chesapeake Bay 

oysters weigh 24 g at the end of the 
first year, 90 g at year 2, 105 g at 

3 years, and 190 g at year 4 (Andrews 

and McHugh 1957). Instantaneous 

monthly growth coefficients range from 

0.42 to 0.84 (Gillmor 1982). In the 

mid-Atlantic region, the minimum 

marketable size of 90 mm is attained 

in 2 to 5 years. 

The growth rate of the oyster is 

1 argely governed by tenperature, 

salinity, i nterti dal exposure, 

turbidity, and food. Growth ceases 

during winter, except in Florida, 

where growth is continuous throughout 

the year (Butler 1952). Growth of 

Virginia oysters is slow and the condition factor is low during spawning 

because energy is used for gamete 

production instead of production of 

body biomass (Haven 1962). Oysters 

expend 48% of their annual energy 

budget in reproduction (Dame 1976). 

After spawning, Florida oysters gain 

weight before they increase in length 

(Butler 1952). Growth of oysters in 

Long Island is greatest in August and 

September after spawning, when 

glycogen reserves are restored 

(Loosanoff and Nomejko 1949; Price et 

al. 1975). 

Environmental conditions affect 

growth. Oysters in a salt pond on 

Long Island in fluctuating salinity 

grow faster than those under 

relatively uniform salinity (Pierce 

and Conover 1954). Oysters in Maine 

exposed for a relatively short time 

during the tidal cycle grow at about 

the same rate as those continuously 

submerged (Gi 1 lmor 1982). Long exposure to the atmosphere, however, 

reduces 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 

differences in rates of growth likely 

are caused by changes in phytoplankton 

composition and abundance. I r, South 

Carolina, oysters grow faster in 

nutrient-rich salt ponds than in tidal 

creeks where primary productivity is 

lower (Manzi et al. 1977). A Walford 

plot predicts that oysters in South 

Carolina would cease growing when 140 

mm long (Dame 1971); however, oysters 

200 mn long occur. 

COMMERCIAL SHELLFISHERIES 

The American oyster has traditional ly supported a valuable industry 

a1 on the eastern seaboard (MacKenzi e 

19833 . Today, the comnercial areas in 

the Mid-Atlantic region (Figure 2) are 

in Long Island Sound, bays along the 

New Jersey coast, Delaware Bay, bays 

along the coast of Maryland and 

Virginia, Chesapeake Bay, and 

A1 bemarle Sound of North Carol i na. 

Landings have decreased from about 100 

million lb during the 1920's 

(Matthiessen 1969) to about 25 mi 11 ion 

1b since the 1960's (Table 1). Oyster 

landings have remained relatively 

stable in Chesapeake Bay from 

1950-1982, whereas 1 andi ngs in the 

rest of the mid-At1 antic region have 

fluctuated more than 10 fold (Table 

1); oyster production declined steeply 

in Chesapeake Bay in 1983-84. 

Maryland and Virginia are the leading 

producers of oysters followed by New 

York (Table 2). Annual landings in 

New York and New Jersey have 

fluctuated as much as 50%, but in 

Connecticut the annual 1 andings have 

fluctuated from 136,000 1b to 1 

million Ib, and in Delaware from 8,000 

to 501,000 Ib. In Long Island Sound, 

persistent set failure is responsible 

for the decline in landings since 1920 

(Matthiessen 1969). A reduction in 

the spreading of shells due to an 

increase in the sale of oysters in the 

shell is partially responsible for the 

decline in abundance of oysters in 

Long Is1 and Sound (MacKenzie 1983). 

Oysters are taken by handpicking 

of clumps from reefs (Bahr and Lanier 

1981), hand and patent tonging from 

boats, and dragging and dredging from 

boats (Korri nga 1976). Dredging has 

made capture more efficient but it 

also increases the potential for 

overharvest and depletion of oyster 
ATLANTIC OCEAN 

MILES 

KILOMETERS 

Figure 2. Commercial production areas for the American oyster in the 

mid-Atlantic. 

7 
Table 1. Oyster landings (thousands of pounds meat weight) by 

geographical region for the years 1950-1982. U.S. Dep . Commerce, 

NOAA, Natl. Mar. Fish. Serv., Natl. Fish. Statistics Program. Annual 

summaries of oyster landings, 1950-1982. 

South Gulf of Year New England Mid-At1 antic Chesapeake Atlantic Mexico 

beds. Harvesting by divers has become 

important in Maryland waters. 

The American oyster is the 

dominant shellfish in mariculture in 

the United States. In 1980, the yield 

of cultured oysters was 23 million lb 

valued at $37 million. This 

production is equal to 55% of the 1980 

U.S. oyster landings. Seed oysters 

are also harvested for transplanting 

to water with insufficient natural 

setting. About 99% of the U.S. seed 

production comes from Virginia waters 

(Alford 1975). 

The equivalences between different values reported for harvest are: 1 
Table 2. Landings (thousands of pounds) of American oyster meats in the 

mid-Atlantic States 1977-1982. U.S. Department of Commerce, NOAA, Natl . Mar. Fish. Serv., Natl. Fish. Statistics Program. Annual summaries of 

oyster landings. 

State MidAtlantic 

Year C T N Y NJ D E MD V A total U.S. total 

bu = 34 1 = 32 kq total weiqht = 7.8 

pints = 3.4 kg meat weightv (Pruder 

1975). 

The market quality of oysters 

depends on the meat size and taste, 

which vary with the season. In 

Florida, the yield of oyster meats per 

shell is best in March just before 

spawning and lowest in the summer 

months during spawning (Rockwood and 

Mazek 1977). In the lower Chesapeake 

Bay, meat yields are best in June and 

again in October and November (Dexter 

S. Haven, Virginia Inst. of Mar. Sci., 

pers. comm.). The reduced yields in 

summer correspond to a reduced 

condition index following spawning 

(Hopkins et al. 1954; Lawrence and 

Scott 1982). Glycogen, which gives 

oysters their sweet taste, is highest 

in flesh of Maryland oysters in April 

and May just before spawning (Sidwell 

et al. 1979). 

Popu 1 at i on Dynami cs 

The vast majority of the eggs and 

larvae produced by American oysters 

perish before setting. Following 

spawning, oyster larvae are abundant 

plankters; densities have ranged f rom 

2,000 to 5,500lkl in Virginia coastal 

waters (Andrews 1979a; Sel iger et a1 . 1982), 100 to 17,000lkl in Long Island 

Sound (Loosanoff and Nomejko 1951), 

and 24,000lkl in Gardiners Bay of Long 

Island Sound (Carriker 1959) and in 

the deeper waters of Delaware Bay 

(Hidu and Haskin 1971). The concentration of larvae near shore in 

Delaware Bay was only 1,000lkl. 

Abundance was greater after high tide 

in the James River Estuary in Virginia 

(Andrews 1979a). In the St. Mary's 

River Estuary in Maryland the numbers 

per kiloliter were 2,000 to 5,000 

straight-hinge larvae, 100 to 1,000 

early umbo larvae, and 50 to 200 late 

umbo larvae (Manning and Whaley 1955). 

The daily mortality of larvae in 

Canada was about 10% (Drinnan and 

Stallworthy 1979), and for spat in 

Massachusetts was about 90% monthly 

(Krantz and Chamber1 in 1978). 

The density of newly set spat 

fluctuates greatly from year to year 

and is different even in adjacent 

areas. Reported densities range from 

0.35-500 spat/shel 1 (Andrews 1949, 

1955; Loosanoff and Nomejko 1951; 

Carriker 1959; Webster and Shaw 1968; 

Kennedy 1980). Typical ly there have 

been 60 spat/bu of natural shells 

(range 0.6 to 72/bu) in the Maryland 

portion of Chesapeake Bay (Krantz and 

Meri tt 1977 ) . Survival of spat in Long Island 

Sound ranged from 0 to 14% in their 
first summer of life (Loosanoff and 

Engle 1940). Spat mortality af 50% to 

70% in Delaware Bay was reduced to 30% 

to 40% when spat were protected by 

screens from 1 arger predators (Tweed 

1973). Survival of spat to seed (3 to 

4 months) in Eastern Bay, Maryland, 

was less than 10% (Engle 1956). 

Survival in estuaries of the Choptank 

River, Maryland, ranges from 1 to 27% 

through the first season (Webster and 

Shaw 1968). Of 314 spat per shell 

that settled, only 14 were still alive 

at the end of the season in the James 

River estuary, Virginia (Andrews 

1949). Spat survival was less in 

dense sets than in sparse sets in the 

James Ri ver, Vi rginia (Andrews 1955) 

and in Chesapeake Bay (Webster and 

Shaw 1968). The number of seed per 

square meter in Long Island Sound was 

200 to 10,000; for 1- to 2-year-olds 

it was 300; and for 3- to 4-year-olds 

it was 75 (MacKenzie 1981). 

The population density of oysters 

in Delaware Bay was about 70 bu/acre 

in natural beds and from 10 to 375 

bu/acre in planted beds (Maurer et a1 . 1971). The density of 70 bu/acre was 

about 80 kg/ha, including shell, or 

about 800 oysters/ha, assuming an 

average weight of 100 g. In 

Chesapeake Bay, the density was about 

70 bu/acre in natural beds and 500 

bu/acre in planted beds (D. S. Haven, 

pers . comm. ) . Ameri can oysters that survi ve 

their first year of life are subject 

to relatively little mortality except 

that inflicted by she1 lfishermen or 

caused by disease outbreaks. In Long 

Island Sound the annual natural 

mortality of adults was only 4%, e.g., 

77% survived after 4 years (MacKenzie 

1981). Adult survival in South Carolina was 85% in a salt pond and 40% in 

an estuary (Manzi and Burrell 1977). 

Mortal i ty was size dependent. Mortal - 

ity of adults 25 to 50 mm long was 19% 

per month in summer (28% in July), 

but those 50 to 75 mm long were 

lost at the rate of 5% per month (near 

0% in July) and those greater than 

75m long died at a rate of less than 

1% per month (Dame 1976). Survival 

was 100% in areas protected from heavy 

waves in North Carolina, and 50% per 

month if exposed to relatively heavy 

waves (Ortega 1981). Mortalities were 

much higher in the areas of Delaware 

Bay and lower Chesapeake Bay where 

oysters were infected with MSX disease 

( Andrews 1968). 

ECOLOGICAL ROLE 

Oyster larvae feed largely on 

plankton, particularly small, naked 

f lagel 1ates (Chrysophyta) , according 

to Guillard (1957). At moderate 

temperatures larval growth is best 

with a diet of naked flagellates, 

whereas at temperatures above 27 OC 

naked a1 gae are scarce and chlorophytes are much more abundant as food 

[Davis and Cal abrese 1964). The 

iarvae, unl i ke adults, do not consume 

bacteria (Davis 1953). Oyster 1 arvae 

are food for a wide variety of filter 

feeders (Andrews 1979a). 

Adult oysters filter large 

quantities of brackish water and 

remove naked flagellates. They most 

effectively filter particles in the 3- 

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

weight of tissue, an oyster held at 

21 OC filters 1.5 l/hr (Palmer 1980). 

At somewhat higher temperatures about 

8 l/hr are filtered (Langefoss and 

Maurer 1975). The volume of water 

filtered per hour was 1,500 times the 

volume of the oyster's body (Loosanoff 

and Nomejko 1946). The filtration 

rate is independent of the available 

food supply, the stage of tide, or 

time of day. If food is absent, 

however, the valves are closed most of 

the time (Higgins 1980). In 

Chesapeake Bay, oysters ingested the 

predominate diatom plankton which 

changes seasonally (Morse 1945). 

Dinoflagel lates, ostracods, small 

eggs, and terrestrial pollen were also 

ingested. 
The oyster is the dominant 

species of a diverse community in 

brackish waters. Over 40 macrofaunal 

species or groups live in oyster beds 

(Bahr and Lanier 1981) and the number 

of species in an oyster comnity 

sometimes exceeds 300 (Wells 1961). 

Oysters were responsible for 88% of 

the respiration of an oyster reef 

(Bahr and Lanier 1981). 

Oysters have a variety of diseases and parasites and are preyed 

uDon bv several carnivores (Galtsoff 

1964). " The bacteria ~ibrio and 

Pseudomonas sometimes ki 11 oysters. 

In the laboratory Vibrio exotoxin at 

47 ~g/1 ki 1 1s oysterembryosw and 

Roland 1984). The protozoan pathoqen 

Perki nsus mari num i n'fects oysters f ;om 

Delaware to Mexico. The 

haplosporidian protozoan Mi nchinia 

nelsoni is responsi ble for thedisease 

md Minchinia costalis for SSO 

(seaside organism) (Andrews 1979b; . . 1982a). ~inchi nia nelsoni , common 

from North Carolina to Massachusetts 

(Krantz et a1 . 1972), caused extensive 

oyster mortality in the Delaware Bay 

in 1957 and in Chesapeake Bay in 1960 

(Andrews 1968). It also killed large 

numbers of oysters in the bays along 

the coast of Maryland and Virginia in 

1960 (Rosenf ield 1971). 

Predators often limit the 

abundance of oysters, especially if 

sal i ni ti es are above 15 ppt (MacKenzi e 

1983). In the mid-Atlantic region, 

the gastropod oyster dri 11s 

(Urosal inx cinerea and Eupleura caud southern oyster dm 

(Thais haemastoma), the whelk (Busycon 

canaliculatum), the starfish (Asterias 

forbesi), and the crab (Cancer irroratus, Call inectes sapidus, and 

Carcinus maenas) destroy large numbers 

of oysterC(7STtsoff 1964). All sizes 

of oysters are killed but small sizes 

are affected most by oyster drills, 

which bore through the shells with a 

combination of chemical dissolution of 

the shell and radular rasping. Small 

oysters are preyed on by crabs and 

starfish. The widespread boring 

sponge Cliona weakens the shell and 

thus lowers qua1 ity (Schlesselman 

1955). S~at are ~reved uDon bv the . " 

f 1 atworm ' Sty1 ochus 'elli$t;;? (MacKenzie 1970; Ch ri stensen 

The bay anemone (Diadumene leucolena) 

consumed 0.6 to 4;9 oyster larvae per 

minute in the laboratory and also 

feeds on larvae in the natural 

environment (Steinberg and K~nnedy 

1979). Over 100 bay anemones/m have 

been known to occupy oyster beds in 

Chesapeake Bay (MacKenzie 1977). The 

southern oyster dri 11 consumes 2.4 

spat/day under optimum conditions 

(Garton and Stickle 1980). In a 

study of oyster mortality in Long Island Sound, MacKenzi e (1981) estimated 

that starfish inflicted 25% mortality 

on spat in 5.5 months, mud crabs 12%, 

and oyster drills 5%. For adult 

oysters near Norwalk, New York, 

starfish cause 3.2% of the annual 

mortality, oyster dri 11s 0.2%, and 

suffocation 0.2%. In New Haven, Connecticut, starfish had no impact, oyster drills killed 0.5%/year, and suffocation killed 2.9%/year. The oyster 

drills are the primary predators of 

oysters in Chesapeake Bay (Lippson 

1973). In the Gulf of Mexico, oysters 

are preyed on by a variety of other 

predators (Cake 1983). 

Major conpetitors of the oyster 

for space on substrate include the 

slipper shells (Cre idula spp.) and 

the jingle shells -f- Anomia spp.) as 

we1 1 as barnacles (Bal anus ebu rneus 

and Chthamalus f ragwand other 

oysters that set on adult shells (MacKenzie 1970; 1983). Shells with heavy 

fouling by barnacles have only about 

25% as many spat as clean shells 

(Manning 1953). Heavy sets of 

barnacles reduce the hard surface 

available for oyster spat and thus 

reduce oyster settlement (Ingle 1951); 

therefore oyster spat are limited to 

areas relatively free of barnacles and 

bryozoans (Beaven 1955). The mussel 

Brachiodontes exustus may also conpete 

with oysters (Ortega 1981). Young 

oysters may be smothered by excreta of 

polychaete worms of the genus 
Polydora, or by excreta of adult 

ovsters (Stenzel 1971). Blooms of red 

t; de (~och 1 odi ni um heterol obatum) at 

concentrations00 cel ls/ml ki 11 ed 

oyster larvae (Ho and Zubkoff 1979). 

Competition by the slipper shells and 

barnacles may limit numbers of oysters 

in Long Is1 and Sound (MacKenzi e 1981; 

1983). Tuni cates and encrusting 

sponges are also major competitors for 

space (D. S. Haven, pers. comm.). 

ENVIRONMENTAL REQUIREMENTS 

The American oyster typically 

lives in shallow, well-mixed estuaries, lagoons, and nearshore bays, and 

tolerates widely fluctuating water 

temperatures , salinities, and 

suspended sol id concent rat i ons 

(Andrews 1979a). Because of the 

tolerance of extreme fluctuations in 

environmental conditions, the environmental requirements of oysters are 

difficult to define. 

Temperature 

Differences in thermal requirements of oysters from different areas 

have led to the postulation that races 

may be separated on the basis of 

different temperature requ i rements 

(Ahmed 1975). Approximate spawning 

temperatures for three distinct races 

were 16 OC for the northern race (New 

England), 20 OC for the mid-Atlantic 

race, and 25 OC for the Gulf of Mexico 

race (Stauber 1950). Menzel (1955) 

found that ciliary activity continued 

at 0 OC in the New England oysters but 

ceased at 6 OC in oysters from the 

mid-Atlantic. Andrews (1979a) 

suggested there are other races as 

well, but genetic studies did not 

closely support the existence of 

physiological races (Bu roker et a1 . 1979). All oysters studied by Buroker 

et al. (1979) were genetically 

identical, except those from Nova 

Scotia and Florida. These populations 

were 82% similar, about the level of 

s i mi 1 arity between the American and 

the mangrove oyster, which can successfully hybridize (Menzel 1968). 

According to Groue and Lester (1982) 

American oysters in Laguna Madre, 

Texas, are genetically distinct from 

four other gulf populations. Measurement of isozymes in genetic studies, 

however, may not validate these races. 

In the mid-Atlantic coastal 

waters, oysters spawn when water 

temperatures are somewhat above 20 "C. 

Gonads do not develop at water 

temperatures below 10 OC, and 16 OC is 

needed for gonadal maturation (Loosanoff and Davis 1952). Exposure to a 

35 OC water temperature accelerated 

gametogenes is and spawning, but subsequent spawning in the same season was 

prevented (Quick 1971). In laboratory 

tests, embryos developed normally at 

water temperatures between 20' and 

30 OC but abnormalities increased 

progressi vely when water temperatures 

declined to 15 OC or rose to 35 OC 

(MacInnes and Calabrese 1979). The 

percentage of abnormal embryos 

increased from 2% at 25 OC to 12% at 

30 OC (Dupuy 1975). The growth of 

larvae was impaired by water temperatures of 30 OC or more and even a 

brief exposure for 10 min at 40 OC 

retarded growth (Hidu et al. 1974). 

In contrast, a temperature range of 

27 to 32 OC is optimum for fastest 

growth and highest survival of larvae 

in Long Island Sound (Davis and 

Cal abrese 1964). 

Adults tolerate water temperatures from a low of -2 OC in New 

England to a high of 36 OC in the Gulf 

of Mexico. At low tide, oysters may 

be exposed to and survive air temperatu res ranging from we1 1 below 

freezing to above 49 OC (Galtsoff 

1964). High temperatu res sometimes 

increase the mortality rate; temperatures above 35 OC for an entire tidal 

cycle may kill some or all oysters 

(Ti nsman and Maurer 1974). The crit i - 

cal thermal maximum for the American 

oyster is 48 OC (Henderson 1929). 
Oysters can tolerate freezing of their 

tissues, and sometimes revive after 

thawing (Loosanoff 1965a). 

Optimum water temperatures for 

carrying out various life functions in 

the adult American oyster are 20 to 30 

OC. Optimum temperatures for maximum 

pumping rates were 20 to 25 OC 

(Collier 1951) or at 28 to 32 OC 

(Loosanoff 1958). Growth stops in 

waters with temperatures below about 8 

OC (Price et al. 1975). Oysters at 2 

to 7 OC are inactive. The threshold 

for feeding is 3 OC (Haven and Morales-Alamo 1966). Exposure to 

unseasonably hi gh temperatures in 

winter stimulates growth if food is 

available (Ruddy et al. 1975). Growth 

is possible between 6 and 32 OC but 

the optimum is about 26 OC (Galtsoff 

1964). 

Salinity 

Oysters prefer waters of 

relatively high salinity. When 

salinity is above about 20 ppt, marine 

predators flourish and destroy large 

numbers of oysters. Oysters usually 

live in brackish waters or in areas of 

unstable salinity that are unsuitable 

for marine predators. In upper 

Chesapeake Bay, for example, spat 

density was positively correlated with 

high salinity , whereas oyster harvest 

was negatively correlated with high 

salinity (lllanowicz et a1 . 1980). 

Salinities above 7 ppt are required for spawning (Loosanoff 1948). 

Embryos developed normal ly at 

salinities of 16 to 30 ppt (MacInnes 

and Calabrese 1979). Larvae tolerated 

salinities of 3 to 31 ppt (Carriker 

1951), but grow fastest and survi ved 

best at salinities above 12 ppt (Davis 

and Calabrese 1964). In Virginia, 

salinities of 20 to 35 ppt were 

requi red for normal embryo development 

and the optimum was 28 ppt (Castagna 

and Chanley 1973). In the laboratory, 

almost no embryos of Long Island Sound 

oysters developed below 15 ppt; the 

percentage progressively increased to 

a salinity of 22.5 ppt (Davis 1958). 

As salinity increased further to 35 

ppt , abnormal i ties increased, and a1 1 

died above 40 ppt. Differences in 

salinity tolerance of larvae are explained by the acclimation of the 

adults before spawning. Larvae 

produced from the spawning of Maryland 

oysters acclimated to the salinity of 

Long Island Sound (26 ppt) had the 

same salinity tolerance as larvae from 

Long Island Sound oysters. Maryland 

oyster larvae, however, were much more 

tolerant of low salinities if the 

parents were acclimated to 9 ppt water 

(similar to Chesapeake Bay). The 

larvae from parents adapted to low 

salinity developed normally at 10 ppt, 

and most survived at 7.5 ppt. 

Development stopped at 22.5 ppt, which 

would be the optimum salinity if the 

parents had been held at higher 

salinities. 

Most larvae in a New Jersey estuary were in the halocline at salinities above 5 ppt (Carriker 1951). 

Larvae of Virginia oysters of parents 

in high salinity water did not 

metamorphose below 17.5 ppt (Castagna 

and Chanley 1973), a finding obviously 

not applicable to populations 1 iving 

in low saline waters. Optimum salinities for the growth of spat in lower 

Chesapeake Bay were 15 to 22 ppt 

(Chanley 1957) and in Long Island 

Sound, 17.5 to 22.5 ppt (Davis 1958). 

Oysters in Chesapeake Bay did not grow 

at salinities below 5 ppt (Abbe 1982). 

Adult oysters tolerate a salinity 

range of 5 to 32 ppt. Outside of 

this range of salinities they discontinue feeding and reproducing. The 

optimum salinity range in Long Island 

Sound is 10 to 28 ppt (Loosanoff 

1965a) and in Delaware Bay, 14 to 28 

ppt (Maurer and Watling 1973). Loosanoff (1965b) found that many oysters 

survive 3 ppt for 30 days. Large numbers, however, die during prolonged 

freshwater inflow from the James 

River, Virginia (Andrews et al. 1959; 

Andrews 1973). Similar observations 

were made in Mobile Bay, Alabama (May 
1972), and in the Santee River, South 

Carolina (Burrel 1 1977). Salinities 

during high freshwater inflow were 

below 2 ppt in the Santee River. Many 

oysters died in the Beaufort Inlet, 

North Carolina, after exposure to a 

salinity near 5 ppt for about a month 

(We1 1s 1961). Oysters in Louisiana 

died after 14 days at 6 ppt (Anderson 

and Anderson 1975). In Delaware Bay, 

oysters survived salinities as low as 

2 ppt (Maurer et al. 1971). The 

length of time oysters survive low 

salinities evidently depends on the 

abruptness of the changes in salinity. 

Low salinities inhibit gonadal 

maturation in oysters in Chesapeake 

Bay (Butler 1949) and Long Island 

Sound (Loosanoff 1953). Reproductive 

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

Substrate and Current 

The preferred habitats in shallow 

estuarine waters are mud flats and 

offshore bars (Hidu 1968), and oyster 

reefs (Bahr and Lani er 1981). Maximum 

density of spat is on horizontal 

surfaces (Clime 1976). 

Oysters grow equally well on 

shells, rocky bottoms, or on thick 

mud, capable of supporting the 

oysters' weight. Soft mddy 

substrates may be improved by adding 

clam or oyster shells. Oyster shells 

from ruddy substrates are more slender 

than those from hard substrates 

(Galtsoff 1964). In Delaware Bay 

mariculture sites, oysters preferred 

to set on the bottom rather than on 

panels suspended in the water column, 

and preferred subtidal waters (Hidu 

1978). 

Currents a re particularly 

important to the larvae and adults of 

the American oyster. Larvae are 

transported by currents. They 

position themselves in the ebb and 

flow of tidal currents to remain in 

estuaries. Excessive currents, 

however, may prevent settlement (Cake 

1983). Since the volume of water immediately above an oyster bed must be 

completely flushed about 72 times 

every 24 hr for maximum feeding, oysters require currents (Galtsoff 1964). 

Tidal flows of 156 to 260 cm/sec or 

higher are needed for optimum growth 

in Mississippi (Veal et al. 1972). 

Currents over oyster bars in Beaufort 

Inlet and the Newport River estuary in 

North Carolina were 11 to 66 cm/sec 

(Wells 1961). Currents of 150 to 600 

cm/sec were measured above oyster bars 

in Delaware Bay (Hidu and Haskin 

1971), and 180 cm/sec in Milford 

Harbor, Connecticut (Prytherch 1929). 

Turbulent currents that carry sand and 

pebbles, however, can damage shells by 

eroding shell surfaces (Galtsoff 

1964). A velocity of 150 cm/sec 

caused unattached oysters to tumble 

along the bottom of Long Island Sound 

(MacKenzie 1981). In Delaware Bay, 

oyster abundance was greatest in areas 

of scour where current kept the beds 

free of sediments (Keck et al. 1973). 

Oysters died in one week if covered 

with sediment at a water temperature 

of 20 OC, and in 2 days if the water 

temperature was 25 OC (Dunnington 

1968). Currents are also necessary 

for removal of pseudofeces and feces 

(Lund 1957). 

Oxygen 

In one study, the hourly oxygen 

consumption was 39 ml/kg for a whole 

animal including the shell or 303 

ml/kg of wet tissue (Hammen 1969). 

Oxygen consumpti on increases with 

increasing temperature; QI0 values 

(the factor by which a reaction 

velocity is increased by an increase 

in temperature of 10 OC) ranged from 

1.2 to 2.3 for gill tissue and 2.7 to 

4.2 for mantle tissue (Bass 1977). 

The rate of oxygen consumption by 

oysters increases as temperature 

increases and salinities decrease 

(Figure 3). Oysters exposed to 

prolonged periods of low salinities 

closed their shells and died of anoxia 
Figure 3. Oxygen consumption in American oyster adults as a function of 

salinity and temperature (Shumway 

1982). 

in the James River and Rappahannock 

River estuaries (Andrews 1982b). Oysters are facultative anaerobes and are 

able to survive daily exposure to low 

oxygen. They also are known to 

survive anaerobically for 3 days after 

spawning (Galtsoff 1964). Oxygen 

consumption is zero when the valves 

are closed (Hamnen 1969). In a study 

in Delaware Bay, oxygen concentrations 

over oyster reefs ranged from 1 to 12 

mg/l (Maurer et al. 1971). The 

decline in oyster harvest in Chesapeake Bay in recent years may be 

caused by decreased concentrations of 

oxygen, although more established 

factors include the outbreak of MSX 

disease in 1981-1983, poor spat set 

for over a decade, and high harvest 

pressure. 

Turbidity and Sedimentation 

Oysters tolerate water with large 

amounts of suspended solids, but the 

pumpi ng rate decreases with increasing 

concentrations of suspended sol ids. 

Pumping is reduced 70% to 85% over the 

range 0 to 1 g/l, depending on the 

nature of the suspended sediment 

(Loosanoff and Tommers 1948). In the 

laboratory the growth of larvae was 

reduced at concent rat i ons of 

particulates above 0.75 g/l (Davis and 

Hidu 1969). In natural environments, 

oysters apparently develop and grow 

better in waters with more suspended 

solids in oyster beds than in waters 

with 1 ess suspended particulates 

(Rhoads 1973). Storms and hurricanes 

may destroy oyster reefs by covering 

them with sediment. 

Acidity 

Oyster embryos devel op normal ly 

within a pH range of 6.8 to 8.8 and 

develop abnormally at a pH above 9.0 

or below 6.5 (Calabrese and Davis 

1966; Calabrese 1972). Larvae 

tolerate the same pH range as embryos 

but growth is fastest at a pH of 8.2 

to 8.5. 

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~0271-r or 

REPORT DOCUMENTATION 7- I. n*clpl.-l s b,:.r*s\ ,,- xe 1 

PAGE 

4. Tdle and subtaste 1 s Reon oste I 

I .. I- 1). SuoplemenIary Nates 

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

Species Profi 1 es: Life Hi stories and Environmental Requirements 

of Coast-a1 Fishes and Invertebrates (Mid-Atlantic)--American --- 

oyster ts 

1986 

1s Abstract (limit: 20Q words) 

7. Author(%) 

Jon G. Stanley -- and Mark A. Sellers 

9. Pedormma Oqanixetlon Name and Address 

Maine Cooperative Fishery Research Unit 

Species profiles are 1 i terature summaries of the taxonomy, morphology, range, 1 i fe hi story, 

and environmental requirements of coastal aquatic species. They are designed to assist in 

environmental impact assessment. The American oyster (Crassostrea vi rginica) i s an important commercial and mariculture species. It is the dominant species in many bays and 

oyster shells form extensive reefs that modify sedimentation and local currents, 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 oysters occur. 

The few surviving larvae cement themselves to solid objects for the remainder o f l i f e . 

-- -----.-.- a. PbflOrmlns Orsantral~on Rem. NO 

__----.-----.--___._ 

10. ~ID~ect/Tash/Work UnaC Re. 

Upable to move, they must tolerate changes in the environment that range from -1.7' 

to 49 OC, 5 to 30 ppt salainity, and clear to muddy water. The distribution and abundance 

of adults are limited by marine predators, so that oysters are limited largely to brackish 

waters. 

313 Murray Hal 1 - A___ 

11. ContrecItC) or GranI(C1 No. 

University of Maine (c) 

Orono, ME 04469 

(C) It Sponsorins Orsenlxmtlon Name end Address 

National Wet1 ands Research Center U. S. Army Corps of Engineers 

Fish and Wildlife Service Waterways Exp. Station 

U.S. Dept. of the Interior P.O. Box 631 

Washington, DC 20240 Vicksburg, MS 39180 

Estuaries Sediments Oxygen 

Oysters Feeding habits Competition 

Growth Life cycles 

Feeding I b. ldenIlfie#a/0ln.Cnded Tmrms 

American oyster 

I ~rassostrea virginica 

Salinity requirements I ~emperature requi renen ts 

C. COSATI fieldIGmup 

- . - - - , - .- . ---- . - - .. . -- 18. Avalleblliiy StatbmmnI 19. fccuraty Class CIhar Reoon) 

Unclassified 

Unclassified Unl imi ted Re1 ease 20. Srcurmly CIarr Uhi* Pas*) 

.-- ---- ..--.- (see ANSI-Z~~.~~) OPTIONAL FORM 272 (em 
TAKE A PRIDE 

212 Amerzcd 

DEPARTMENT OF THE INTERIOR 

U.S. FISH AND WILDLIFE SERICE 

As the Nation's principal conservation agency. the Department of the Interior has responsibility for most of 0ur.nationally owned public lands and natural resources. This includes 

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

preserving thsenvironmental 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.