REFEqENCE COPY Do Not Remove from the Library 11 S. Fish and Wildlife Service Biological Report 82 (11.53) NationalWetlands Research Center TR EL-82-4 June 1986 700 Cajun Dome Boulevard Lafcryette, Louisiana 70506
Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (North Atlantic) SOFTSHELL CLAM
Coastal Ecology Group Fish and Wildlife Service Waterways ~xperimentStation U.S. Department of the Interior U.S. Army Corps of Engineers Biological Report 82(11.53) TR EL-82-4 June 1986
Species Profiles: Life Histories and Environmental Requirements of Coastal Fish and Invertebrates (North Atlantic)
SOFTSHELL CLAM
Carter R. Newel1 Maine She1 lfish Research and Development Damariscotta, ME 04543
and Herbert Hidu Department of Ani ma1 and Veterinary Sciences University of Maine Orono, ME 04469
Project Officer John Parsons 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 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 coaxal 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:
Newell, C.R., and H. Hidu. 1986. Species profiles: life histories and envi ronmental requi rements of coastal fishes and invertebrates (North Atlantic) -- softshell clam. U.S. Fish Wildl. Serv. Biol. Rep. 82(11.53). U.S. Army Corps of Engineers, TR EL-82-4. 17 pp. PREFACE
This species profile is one of a series on coastal aquatic organisms, principal ly 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, 1ife history, ecological role, environmental requirements, and economic importance, if appl icable. A three-ri ng 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 following addresses.
Information Transfer Special ist National Coastal Ecosystems Team U.S. Fish and Wildlife Service NASA-Slidell Computer Complex 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
To Obtain mill imeters (mn) inches centimeters (n) inches meters (m) feet ki1 ometers ( km) mil es 2 square meters (m ) 10.76 square feet square ki1 ometers ( km2) 0.3861 square 'nil es hectares (ha) 2.471 acres liters (1) gal 1ons cubic meters (m3) cubic feet cubic lneters acre-feet milligrams (mg) 0.00003527 ounces grams (g) 0.03527 ounces kilograms (kg) 2.205 pounds metric tons (t) 2205.0 pounds metric tons 1.102 short tons ki1 ocal ories ( kcal ) 3.968 British thermal units
Celsius degrees 1.8("C) + 32 Fahrenheit degrees
U.S. Customary to Metric inches 25.40 mil 1imeters inches 2.54 centimeters feet (ft) 0.3048 meters fathoms 1.829 meters miles (mi) 1.609 kilometers nautical miles (mi) 1.852 ki1 oneters square feet (ft2) square meters acres 2 hectares square miles (mi ) square kilometers gallons (gal ) 3.785 1i ters cubic feet (ft3) 0.02831 cubic meters acre- feet 1233.0 cubic meters ounces (oz) 28.35 grams pounds (lb) 0.4536 ki1 ograms short tons (ton) 0.9072 metric tons British thermal units (Btu) 0.2520 ki1 ocal ories Fahrenheit degrees 0.5556("F - 32) Celsius degrees Page
PREFACE ...... iii CONVERSION TABLE ...... iv ACKNOWLEDGMENTS ...... vi NCIMENCLATLIRE /TAXONOMY /RANGE ...... 1 MORPHOLOGY/IDENTIFICATION AIDS . . . 1 REASON FOR INCLUSION IN SERIES ...... 3 LIFE HISTORY ...... 3 Spawning ...... 3 Fecundity and Gametes ...... 4 Larvae ...... 4 Juveni 1e Seed Clams ...... 5 Adult Clams ...... 5 COMMERCIAL/SPORT FISHERIES ...... 6 POPULATION DYNAMICS ...... 6 GROWTH CHARACTERISTICS ...... 7 ECCILOGICAL ROLE ...... 8 Food and Feeding Habits ...... *a. 8 'Predators ...... 8 ENVIRONMENTAL REQUIREMENTS ...... 9 Salinity ...... 9 Temperature ...... 9 Oxygen ...... 10 Substrate and Current ...... 10 Pollution ...... 11 LITERATURE CITErl ...... 13 ACKNOWLEDGMENTS
Dana Wallace and Walter Foster, Maine Department of Marine Resources, Augusta, Maine, and John Mori ng, Maine Cooperative Fishery Research Unit, University of Maine, kindly reviewed the manuscript. Figure 1. The softshell clam (figure courtesy of the Maine Sea Grant Program).
SOFTSHELL CLAM
NOMENCLATURE/TAXONOMY/RANGE MORPHOLOGY/IDENTIFICATION AIDS Scientific name ..... Mya arenaria L. The softshell clam sometimes Preferred common names ... softshell exceeds 10 cm in length (all lengths clam, steamer clam, nannynose in this report are shel 1 lengths). The (Figure 1). shape of the shel 1 is elongate and Other common names .... sand gaper, elliptical. The clam has a large long-necked clam siphonal gape on the slightly pointed Class ...... Rivalvia and elongate posterior end, and there (Pelecypoda) is a small pedal gape on the anterior Order ...... Eulamellibranchia end (Stanley 1970). The shell exter- Suborder...... Heterodonta ior has numerous growth lines; each Family Myidae usually represents 1 year's growth or ...... an envi ronmental disturbance (Schuster 1951) . On live specimens, the exterior of the shell is rugose and is covered with a protein layer called the periostracum. Empty shel 1s turn Geographical Range: Intertidal and chalk white after the periostracum subtidal to depths of 100-199 m erodes away. On large 1ive specimens, along the Atlantic coast from the long contractile siphon may extend Labrador to South Carolina and as far as 20 cm to reach the sediment extending, in lesser abundance, surface. The foot is small and south to Florida; throughout muscular and the mantle lobes are western Europe; successfully fused except at the pedal gape and at introduced in Pacific coastal the ends of the siphon tubes. The end waters of Alaska and California of the incurrent siphon has a ring of (Theroux and Wigley 1983). The tentacles. The adductor muscles are softshell clam is most abundant unequal in size (anisomyarian). intertidally along the New England coast (~igure' 2) and The compact hinge 1i gament is subtidally in Chesapeake Bay. attached to the right valve and is A TL A N TIC OCEAN
Figure 2. Distribution of the softshell clam in the North Atlantic Bight. C enclosed by the chondrophore of the LIFE HISTORY left valve (Figure 1). The valves are thin, and mean ratios of length (L), The softshell clam has seven life width (W), and height (H) are: L/H- history stages (Table 1). 1.65, H/W-1 (Stanley 1970). Newel 1 and Hidu (1982) observed mean L/W ratios of 2.6 in clams from gravel Spawning beds, and 3.2 in clams from sand beds. Sexual maturation of the soft- shell clam depends upon the size of REASON FOR INCLUSION IN SERIES th~clam rather than its age. Clams longer than 20 mm in shell length are The softshell clam is a dominant usually capable of spawning (Coe and member of many estuarine soft-bottom Turner 1938). Clams from cold Maine communities and is commercial ly waters may spawn at a smaller size important along much of the North than those from Massachusetts or Long Atlantic coast. In New England, it is Island Sound. Sexes are separate, the the second most important commercial sex ratio is 50:50, and males are in- clam after the hard clam (Mercenaria distinguishable from females unless a mercenaria) . In 1978, U.S. landings gonad smear is examined under a micro- yielded about 4.6 million kg (10.1 scope. A low incidence of hermapro- million 1b) of meats (Pileggi and dites is common in most populations. Thompson 1979). Its inshore The seasonal development of the gonads distribution, however, makes it was summarized for the north Atlantic vulnerable to contamination by munici- coast by Ropes and Stickney (1965). pal sewage, industrial effluent, and Gametogenesis begins in late winter coastal construction projects. Also, and early spring, and spawning peaks the adults usually live in permanent from June to September, depending upon burrows, so excessive siltation can location. suffocate them. The construction of piers and jetties that alter clam Clams usually spawn once a year habitat is likely to have long-term north of Cape Cod, and twice a year adverse effects on clam populations. south of Cape Cod. The differences in
Table 1. The life stages and characteristics of the softshell clam.
--- Ase or -- Stage characteristic Ferti 1 i zed egg 0-12 hours old. Trochophore 13-24 hours 01 d, top-shaped. Vel iger 10-20 days old, has a shel 1 and swims by using a velum. Prodissoconch I Has straight-hinged shel 1. Prodissoconch I1 Has umbo on shel 1. Spat (Dissoconch) Bottom-dwel 1i ng, after settlement and velum cast off. Juveni 1e Up to 20 rrm shell length. -Adult Sexual ly mature. the spawning habits demonstrate the shellfish hatchery in Maine, females importance of water temperature on 60-70 mm long released about 1 million gonad maturation and spawning. In eggs (S. Chapman, Ira Darling Center, Maryland, the clams spawn in April University of Maine, Walpole, pers. when water temperatures reach 10 "C comm.) . Ferti 1ization is external. and the abundance of larvae peaks when The egg, when released into seawater, the spring water temperatures are is spherical, 66 microns in diameter, about 20 "C. Gametogenesis for the white, and gelatinous (Belding 1930). second spawning began when water The sperm has a head which measures 4 temperatures dropped below 25 OC, microns in diameter and a long according to Pf itzenmeyer (1965). whiplike tail. The fertilized eggs Brousseau (1978a) observed an early may be carried by the current many spawn (March-Apri 1) in clams from miles from the spawning site. The Ipswich Ray, near Gloucester, Massa- percentage of energy that goes into chusetts, characterized by rapid the reproducti ve process increases maturation and gamete re1ease. The with an -increase in the size of the clams spawned again in June and July, clam. The oldest and largest and the number of eggs and sperm individuals in the population released in the summer was greater contribute most of the eggs. than in the spring.
Food availability also is an important factor in determining the Larvae timing and intensity of spawning. In shel lfish hatcheries, clams are ex- The larval stage lasts from 12 to posed to slightly elevated tempera- 14 days in southern Massachusetts, tures and optimal algal diets to about 14 days in Chesapeake Bay, and stimulate rapid gametogenesis and egg up to 21 days in Maine (Belding 1930; "ripeness." Exposure of broodstock to Pf itzenmeyer 1972). After hatching periods of alternating warm and cold (in 9 h at 27 OC) the embryo quickly temperatures stimulates spawning changes into a top-shaped, spinning (Loosanoff and Davis 1963). On a t rochophore (Be1di ng 1930; Hanks Maine mud flat, spawning was observed 1969). Soon, the larva forms its when inshore seawater temperatures first shel 1 and a swimming organ (the reached a seasonal maximum of 21 "C velum) and becomes a prodissoconch I (Newel1 1982). During the last week (or early veliger stage). It is about of June, water temperatures fluctuated 80 microns long. When growth begins between 13 "C (at high tide) and 21 "C at the shell periphery, the (on a sunny day in shallow water at prodissoconch II (or 1ate vel iger) low tide). Males usually spawn first, larval stage begins. Loosanoff and releasing pheromone and sperm into the Davis (1963) and Loosanoff et al. water, which cause the females to (1966) give measurements and pictu res spawn. of development of the softshell clam up unti 1 settlement. The larvae may be identified by hinge structure (Lutz Fecundi ty and Gametes et a1 . 1982). Along the New Hampshi re coast from June to October, the number In Massachusetts, a female clam of veligers in the lankton was as 63 mm long is capable of releasing as high as 1,00O/m (Normandeau many as 3 mil 1ion eggs a year (Belding Associates Inc. 1978). Density peaked 1930), but according to Brousseau in late summer. Larval abundance was (1978a), female clams from the middle higher in inshore waters than offshore intertidal zone at Cape Ann, waters and higher at depths from 5 to Massachusetts, produce only 120,000 9 m than near the surface or at a eggs a year. In an experiment in a depth of 13 m. At the end of the larval stage, Because adult softshell clams are the clam attaches to the bottom. Then sedentary, maintenance of each the velum is cast off and a foot pop~~lationdepends upon the settlement develops as the clam metamorphoses of spat or the movement of juvenile into a bottom-dweller called a spat. seed clams. Because of the influence Metamorphosis may be delayed later of oceanographic conditions on re- than usual, until the clam locates a cruitment, the abundance of settling suitable substrate for attachment. clams (the set) may be irregular in some locations ; for example, enormous quantities of seed clams may be concentrated in small area. A clam Juveni le Seed Clams set of 538,00O/m 4 was reported in an eddy adjacent to a sand bar in Plum After metamorphosis, the young Island Sound, Massachusetts (Beldi ng spat (0.25 - 1 mm long) may undergo a 1930). The density of seed clams floatin - crawling stage for 2 to 5 usually is greatest in eddies, along weeks qselding 1930). During this the sides of sand bars or islands, at stage the clam spat sometimes holds on the mouths of rivers or Streams to the substrate using a byssal emptying into shallow water, or in thread. The spat may first attach to slack water adjacent to a swift eel grass, filamentous algae, and other current. Because of their small size objects in the subtidal zone (Kellogg and shallow burrowing depth, juvenile 1900), but as it continues to grow the clams are subject to intense pre- spat drops to the bottom and burrows dation. The densit of juvenile clams into the sediment. After the clam approached 6.000/$ in the subtidal becomes large enough to be noticed by zone in Virginia, but dropped to zero clam diggers (5 mm), it is referred to 1 month later, presumably due to as clam "seed" until it reaches market predation (Lucy 1976); however, clams size. Juvenile seed clams may mi grate in Chesapeake Bay were able to avoid up to several hundred yards towards most predators by burrowing as deep as shore (Dow and Wallace 1961). The 10 cm (Blundon and Kennedy 1982). byssus is used for attachment while Vegetation reduced predation of juvenile clams up to 13 mm' long move softshell clams in the subtidal zone. or burrow. The movement of juveni les from subtidal areas to the intertidal zone The movement of seed clams 2-15 in New England also reduces predation. mm long on a Massachusetts beach was For example, experimental plantings of studied by Matthiessen (1960b). Clams seed clams at different intertidal 2-3 mm long that set in late summer elevations along the Maine coast remained in the seaward portion of the revealed that growth is slowest but sampling area for 8-10 months (until survival is the greatest in the upper April, May, or June) and grew to 5 mm intertidal zone (Newel 1 1982). or more, and then moved shoreward. This movement was attributed to hydrodynamic forces such as sediment sorting by shoaling waves. During spring storms, clams 5-15 mm long Adult Clams showed a net horizontal displacement shoreward along with coarse sediment In suitable habitat, the particles (Matthiessen 1960b). The softshell clam makes a substanti a1 movement of first-year juveniles contribution to the biomass of the peaked in September and October during benthic community. For example, 1 ha early growth, and again in May after of mudflat containing clams ab2ut 62 growth resumed in the spring (Dow and mm long at a density of 269/m con- Wallace 1961). tains 1,442 bushels of clams in the shell, and 21,635 lb of meats (D. dity. Less than 0.1% of the eggs Wal lace, Maine Dep. Marine Resources, produced in a spawning season result Augusta, pers. corn.). in a successful settlement, and about 1% of the settled spat must mature and reproduce in order to sustain the populations. Mortality is heavy in the planktonic stage and immediately COMMERC IAL/SPORT FISHERIES after settlement, and decreases as the clam grows older. As the shell becomes thicker and the clam digs The softshell clam is a valuable deeper, its survi val rate increases. sport and commercial species. The Survival rate follows an exponential sport fishery is locally important to decay, leveling off after 3 years of coastal resort towns, where clam age. Mortality rates are highest in ordinances strictly regulate the summer when predators are most catch. In New England, where the abundant (Brousseau 1978b). Fecundity resource is primarily intertidal, the increases with clam size, so the commercial instruments are generally intrinsic rate of natural increase is constrained by law to hand implements. high. The high mortality of larvae is Clam forks and hoes are common offset by the high intrinsic rate of instruments, a1 though dredges are natural increase (Brousseau 1978b). sometimes used in subtidal areas in Massachusetts and experimental ly in Densities of larvae ranged from Maine. In Chesapeake and Delaware 0.1 to l,000/m3 in New Hampshire Bays, where the resource is subtidal, waters of the Gulf of Maine clams are harvested with a hydraulic (Normandeau Associates, Inc. 1978) and escalator dredge. Damage to clams is the late veliger larval densities less from dredges than from forks and ranged from 0 to 1,400/m3 in hoes (Kyte and Chew 1975). Burial and Chesapeake Bay (Pfi tzenmeyer 1962) breakage of clams during hand har- during the summer months. In one vesting sometimes reduces production study, settlement densities as high in New England (Glude 1954). Hydrau- as 107, 600/m2 (10,00O/f t2),decreased lic clam rakes have been used in Cana- to 21,500/m2 (2,000/ft2) 2 months da (Bourne 1967) and Maine to collect later, and then to 0 after 1 year seed clams for transplanting. Annual (Turner 1953). U.S. commercial landings of softshell clams from 1977 to 1981 averaged 4.2 In Chesapeake Bay, spat (less million kg (9.3 million lb), worth $15 than 10 mm long) densities decreased million. At one time, sewage polluted from 500/m2 in December to less than many of the clam beds along the New 10/m2 by June (Blundon and Kennedy England coast, so they were closed to 1982). In New Hampshire, densities diggers and dredgers. In the 19701s, of young-of- the-year spat ranged f rom the construction of municipal sewage 21/m2 to 8,200/m2 from 1971 to 1980. treatment plants sharply increased and High larval densities (530/m3 in the pollution decreased, so some of the summer of 1975) were followed by high beds have been reopened and producti on spat densities (8,200/m2) in 1976; has proportionately increased. adults of the 1975 year class produced a strong fishery from 1978 to 1980 (Savage 1981). POPULATION DYNAMICS In Casco Bay, Maine, standing Because the mortality of eggs, crops in 1979 averaged 90 to 120 larvae, and seed clams is extremely bushels of clams per acre. The total high, clam populations are maintained inventory of the bay was 107,500 only because of a tremendous fecun- bushels (Card 1980). Adults have an aggregated distri- (1979). In New England, softshell bution, limited primarily to inter- clams generally grow fastest in late tidal and shallow subtidal areas spring and early summer, and slowest (Saila and Gaucher 1966; Commito in the cold winter months (Belding 1982). The degree of aggregation may 1930; Brousseau 1979). The months of depend upon the slope of the inter- rapid clam growth are coincident with tidal area and current (Newcombe rising abundance of phytoplankton and 1936). Juveni les may concentrate near seawater temperature in the Gulf of a steep shore profile (Matthiessen Maine (Bi gelow 1917; Petrie 1975). 1960b). Aggregation also may be Also, rapid clam growth in a salt pond caused by predation, by hand in Martha's Vineyard, Massachusetts, harvesting or dredging, and by the was coincident with a high abundance concentration of spat by hydrographic of f lagel lates (Matthiessen 1960a). conditions . Seasonal variations in growth rates are positively correlated with seasonal changes in biochemical GROWTH CHARACTERISTICS (glycogen) 1evels and condition indices (measurements of shellfish The softshell clam grows rapidly "fatness"). Glycogen levels and meat in a favorable environment. Clams yields are high in the spring; the usually reach market size (2 inches glycogen is converted to gametes with long) in 1.5 years in Chesapeake Bay, a subsequent drop in meat yields (Pfitzenmeyer 1972), in 2 to 3 years during the spawning season, and the in Rhode Island and Massachusetts meat yield recovers after spawning (Turner 1948; Brousseau 1979), in 3 to (Newell 1982). In Maine, glycogen in 6 years in Maine, and in 5 years in shellfish of good market quality peaks New Brunswick , Canada (Turner 1948; in late spring and is lowest in win- Spear and Glude 1957; Cormito 1982). ter. Growth may be modeled using the expo- nential von Bertalanffy growth Growth rates are also closely equation, expressed by the fol lowi related to current, sediment type, and formula: Shell length = a(l - be-kf? intertidal height. Clams grow the where a, b and k are constants derived fastest in soft sediments on the lower from growth data, and t = time. shore (where food is relatively Growth rate constants of clams from abundant) under good current different geographi c areas were conditions in New England (Belding calculated by Brousseau (1979). Data 1930; Newel1 1982). In a laboratory fit to the growth equation using best experiment, clams grew faster in soft fit computer-generated curves demon- mud or sand than in gravel (Newel1 and strate widespread differences in Hidu 1982). Similarly, shell form and growth rates among 1ocati ons . percent shel 1 weight varied with Seasonal variations in growth rates growth rate, sediment type, and can be incorporated into the von intertidal height. Slow-growi ng clams Bertalanffy equation by adding from coarse sediments and from the temperature, in day-degrees upper shore (where food is relatively (Munch-Peterson 1973). scarce) have higher percent shel 1 weights and larger shel 1 1ength-depth Seasonal variations in growth regression slopes (greater shell rates have been attributed in part to globosi ty) than fast-growing clams food avai 1abi 1i ty by Newcombe (1935), from the lower shore and from soft Matthiessen (1960a), and Stickney sediments. (1964); to temperature by Belding (1930), Dow and Wallace (1961), Excessive density can also limit Stickney (1964), and Munch-Peterson growth rates because of competition (1973): and to spawning by Brousseau for food and space. Mature clam densities of 161-269/m2 are general ly silts in high concentrations, and may considered favorable for good growth sort algal cells from inorganic (Be1 di ng 1930). particles prior to ingestion. Clams of 0.3 g dry meat weights continue to filter even if seawater silt particle ECOLOGICAL ROLE densities exceed 300 mg/l (Eaton 1981). High levels of oil pollution Food and Feeding Habits in sediments (hydrocarbon levels over 1,500 ppm) caused a reduction in food Clam larvae, juveniles, and filtration rates and a lower carbon ad1~1tS feed by filtering seawater. flux in clams from Maine (Gilfillan et Postmetamorphic clams draw in through a1 . 1976). According to Matthiessen the incurrent siphon by beating the (1960b), filtration rates of clams gi 11 cilia. The water passes through decl ined when exposed to salinities the gills, where food particles are between 8 and 15 ppt and stopped when removed, trapped in mucus, and swept salinities were below 4 ppt. Clams to the mouth. Particles too lar e for continue to filter when seawater ingestion, inorganic particles 4ow in temperatures are below 3 OC, but food nutrition, and particles of any type assimilation is low. in dense concentrations in seawater are usually rejected by ciliated structures called the labial palps. Predators These particles are expel led through the incurrent siphon as pseudofeces by Predation is one of the most a rapid contraction of the adductor important factors in the control of muscles. Phytoplankton cell natural populations of softshell concentrations greater than 30,000/ml clams. Planktonic larvae are subject of seawater cause a reduction of to predation by other planktors, fish, filtration rates and the formation of and f i1 teri ng invertebrates; young pseudof eces as undi gested a1 gae and spat may be devoured by birds, fish, mucus (Stickney 1964). shrimp, worms, crabs, snails and flatworms. As the juvenile clam Flagellates and diatoms are the grows, it burrows deeper into the preferred diet, although clams can substrate, where it finds fh',otection obtain nutrition from bacteria and from most predators. rapid organi c detritus in res1.1spended juveni 1e growth and postponement of mudflat sediments (Eaton 1981) and gametogenesis are considered to be dissolved organic molecules (Stewart adaptations for survi va1 (Commito and Bamford 1976). In a salt pond in 1982). In one instance, it was Massachusetts, clams grew faster on a estimated that in Massachusetts the diet of flagellates than on diatoms mummi chog (Fundulus heteroclitus), a (Matthiessen 1960b). small fish, consumed as many as 546,000 softshell clams (
The characteristics of the Pollution sediments reflect the rates of the bottom currents and establish, from a Softshell clams in polluted water physical standpoint, the suitabi lity accumulate pesticides (Dow 19721, oi 1 of the bottom for clams. Coarser (Mayo et al. 1975), heavy metals sediments usual ly reflect faster (Eisler 1977), and sometimes the currents, which support greater hacteria and viruses in municipal population densities and cause faster sewage. Toxic materials are most growth (Appeldoorn 1982). If the cur- damaging to fertilized eggs and rents are too slow, the sediments larvae, and less damaging as the clams usually have a high silt-clay content, grow larger. Oil pollutants can cause which, in excess, can clog the gi 11s a reduction in the carbon flux of of the clams, reduce growth rates, and clams (Gilfillan et al. 1976). More in extreme cases cause smothering (Dow refined petrochemicals may have a and Wallace 1961). Most clams in greater effect on the incidence of Chesapeake Bay thrive in a substrate pathological tumors in clams than that is less than 50% silt (Pfitzen- unrefined oils and heavy metals meyer 1972). Clams may continue (Walker et al. 1981). Clam larvae are pumping when total suspended sol ids sensitive to chlori ne-produced exceed 300 mgll, but the production of oxidants but in general adu 1t clams mucus and the loss of energy during are relatively tolerant of pollution the ejection of pseudofeces strain the (Brown et al. 1977). Despite the energy budget of the clam (Eaton tolerance of softshell clams to 1983). pol lution, hacteria and vi ruses from municipal effluent accumulate in the Coarse sediments and mats of clam's body tissues, and if eaten, are vegetation help protect clams from a threat to public health. Until most predators (Blundon and Kennedy municipal pollution is adequately 1982). During winter months when abated, clamming in some waters will phytoplankton populations are lowest, continue to be prohibited.
LITERATURE CITED
Allen, J.A., and M.R. Garrett. 1971. arenaria, f rom Cape Ann, The excretion of ammonia and urea by Massachusetts. U.S. Natl . Mar. Fish. Mya --arenaria L. (Mollusca: Serv. Fish. Bull. 76: 155-166. Bival via). Comp. Biochem. Physiol. 39A: 633-642. Brousseau, D.J. 1978b. Population dynamics of the soft-shell clam Mya Appeldoorn, R .S. 1982. Variation in arenaria. Mar. Biol . (N.Y.). the growth of Mya arenaria and 50: 63-71. its relation to the environment an analyzed through principal Brousseau, D.J. 1979. Analysis of components analysis and the W growth rate in MJ~ arenaria using parameter of the von Bertalanffy the von Bertalanff e uatioK Mar. equation. U.S. Natl. Mar. Fish. Biol. (N.Y.). 51: &'I-$27. Serv. Fish. Bull. 81: 75-84. Brown, R.S., R.E. Wolke, S.R. Saila, Beldi ng, D.L. 1930. The soft-she1 led and C.W. Brown. 1977. Prevalence of neoplasia in ten New England clam f isher-y of Massachusetts. of the soft-she1 1 clam Commonw. Mass. Dep. Conserv., Di v. Ann. N.Y. Acad. Sci. Fish Game, Mar. Fish. Ser. 1. 65 pp.
Bigelow, H.R. 1917. Exploration of Card, D.J. 1980. Casco Bay marine the coast water between Cape Cod and resources inventory: soft-shell clam Halifax in 1914 and 1915, by the survey 197911980. Maine Dep. Mar. United States Fisheri es Schooner Resour. Res. Ref. Doc. 80120. Grampus. Oceanography and plankton. Bull. Mus. Comp. Zool. Harvard. 59: Coe, W.R., and J.J. Turner, Jr. 1938. 161-357. Devel opment of the gonads and gametes of the soft shell clam (Mya Blundon, J.A., and V.S. Kennedy. 1982. ---arenaria). J. Morphol. 62: 91-111. Refucles for infaunal bival ves f rom blue- crab Callinectes sa idus Collip, J.B. 1920. Studies on (Rathbun). J. ~miol-!kT mol luscan coelomic fluid. Effect of change in environment on the carbon dioxide content of the coelomic Rourne, J. 1967. Digging efficiency fluid. Anaerobic respiration in M a trials with a hydraulic clam rake. --arenaria. J. Biol. Chem. 45: 23-3& Fish. Res. Board-can. Tech. Rep. 15: 1-23. Commit~, J.A. 1982. Effects of Lrlnatia herus predation on the Brousseau, D.J. 1978a. Spawning population dynamics of Mya arenaria cycle, fecundity, and recruitment in and Macoma balthica inMaine, USA. a population of soft-shell clam, Mya Mar. Biol. (N.Y.).9: 187-193. Creaser, E.P., and D.A. Clifford. Glude, J.B. 1954. Survival of 1977. Salinity acclimation in the soft-shell clams, M arenaria, soft-shell clam, Mya arenaria. U.S. buried at various depths. Maine Dep. Natl. Mar. Fish. Serv. Fish. Rull. Sea Shore Fish. Res. Bull. 22. 26 75: 225-229. PP.
Dow. R.L. 1972. Pesticides in fish Hanks, R .W. 1969. Soft-she1 1 clams. and shellfish. Maine Sea Shore Fish. Pages 112-119 -in F.E. Firth, ed. The Res. Bull. 32. 5 pp. encyclopedia of marine resources. Van Nostrand Reinholdt Co., New Dow, R.L., and D.E. Wallace. 1961. York. 740 pp. The soft-shell clam industr.y of Maine. U.S. Fish Wildl. Serv. Circ. Harrigan. R.E. 1956. The effect of 110. 36 pp. temperature on the pumping rate of the soft-she1 led clam, -Mya arenaria. Eaton, J .S. 1981. Seasonal patterns M.S. Thesis, Columbian College, and rliscriminatiorl in the feeding George Washington University. behavior of the soft-she1 led clam; Washington, D.C. 54 pp. -Mya arenaria.-- Pages 3-14 in-- Proc. 8th Ann~r. Conf. Clam Res., Maine Kel logg, J .L. 1900. Observations on Dep. Mar. Resotrr., Boothbay Harbor. the life history of the common clams, M a arenaria. U.S. Fish. Eaton. J.S. 1983. Seasonality and Bull. (1& 19: 193-202. discrimination in the feeding behavior of the soft-she1 led clam, Kelso, W.E. 1979. Predation on soft-shell clams, Mya arenaria, by -Mya ---arenaria, and a review of lamel li branch bivalve feeding. M.S. the common mummichog, Fundulus Thesis, University of Maine, Orono. heteroclitus. Estuaries 2: 249-254. 146 pp. Kennedy, B.S., and J. A. Mihursky. Edwards, D.C., and J.D. Heubner. 1977. 1972. Effects of temperature in the Feeding and growth rates of respi ratory metabol ism of three Polinices duplicatlls preying on Mya ~hesa~eake-bivalves. Chesapeake arenari a at Barnstable Harbor, Sci. 13: 1-22. Massachusetts. Ecol ogy 58 : 1218-1236. Kyte, M., and K. Chew. 1975. A review of the hydraulic escalator shellfish Eisler, R. 1977. Toxicity evaluation harvester and its known effects in of a complex metal mixt~rreto the relation to the soft-she1 1 clam, Mya softshell' clam Mfl arenaria. Mar. arenaria. Wash. Sea Grant 75-2. Biol. (N.Y.). 43:- 265-m- Division of Marine Resources. University of Washington, Seattle. Fong, W.C. 1976. Uptake and retention 32 PP- of Kuwait crude oil and its effects on oxygen uptake by the soft-shell Lawson, D. 1966. The genus Mya in the clam, My2 arenaria. J. Fish. Res. Board Can. 33: 2776-2780. Arctic region. Ma1 acoGji'a 3: 399-418. Gilfillan, E.S., D. Mayo, S. Hanson, D. Donovan, and L.C. Jiang. 1976. Loosanoff, V.L., and H.C. Davis. 1963. Reduction in carbon flux in Mya Rearing of bivalve mol lusks. Pages arenaria- caused by a spill of No. 6 1-136 in Advances in marine biology. fuel oil. Mar. Biol. (N.Y.). F.S. RTssell, ed. Academic Press, 37: 115-123. London. Loosanoff, V.L., H.C. Davis, and P.E. National Marine Fisheries Service Chanley. 1966. Dimensions and (NOAA). 1982. Fisheries of the shapes of larvae of some bivalve United States, 1981. U.S. Natl. mollusks. Malacologia 4: 351-435. Mar. Fish. Serv., Curr. Fish. Stat. No. 8200. 117 pp. Lowe, G.A., and E.R. Trueman. 1972. The heart and water flow rates of Newcombe. C.L. 1935. Growth of Mva
.-Mya arenaria (Bi val via: Mol lusca) at arenaria in the Bay of Fundy regi%< different metabolic levels. Corrp. Can. J. Res. 13: 86-137. Riochem. Physiol . 41A: 487-494. Newcombe, C.L. 1936. A corrparative Lucy, J.A. 1976. The reproductive study of the abundance and rate of cycle of Mya arenaria L. and growth of Qa arenaria I-. in the distribution of juvenile clams in Gulf of St. TaFenCeand Bay of the upper portion of the nearshore Fundy regions. Ecology 17: 418-428. zone of the York River, Virginia. M.S. Thesis, The College of William Newel 1, C.R. 1982. The soft-she1 led and Mary, Wi1 liamsburg, Virginia. clam Mya arenaria-- L.: growth rates, 131 pp. growth allometry, and annual growth 1ine formation. M.S. Thesis. Lutz, R., J. Goodsell. M. Castagna, S. University of Maine, Orono. 142 pp. Chapman, C. Newell, H. Hidu, R. Mann, D. Jablonski, V. Kennedy, S. Newel 1. C.R., and H. Hidu. 1982. The Siddall, R. Goldberg. J. Beattie, C. effects of sediment type on growth Falmagne, A. Chestnut, and A. rate and shell allometry in the Partridge. 1982. Prel irni nary soft-she1 led clam Mya arenaria L. J. observations on the usefulness of Exp. Mar. Biol. EcKW7TPF295. hinge structures for identification of bivalve larvae. J. Shellfish. Norrnandeau Associates, Inc. 1978. Res. 2: 65-70. Seabrook ecoloqical studies. Pub1 ic Service ~om~any,Tech. Rep. Nashua. Matthiessen, G.C. 1960a. Observations N.H. on the ecology of the soft clam, Mya arenaria, ii a salt pond. Limnol. Petrie, W.M. 1975. Distribution and Fern. 5: 291-300. seasonal fluctuation of the phytoplankton in the upper Matthiessen, G.C. 1960b. Intertidal Damariscotta River Estuary, Lincoln zonation in populations of Mya County, Maine. M.S. Thesis. arenaria. Limnol . Oceanogr. 5: University of Maine, Orono. 129 pp. 381-388.
Mayo, F.W.. C.G. Cogger, D.J. Donovan, Pf itzenmeyer , H.T. 1962. Periods of R.A. Gambardella, L.C. Jiang, and J. spawning and setting of the Quan. 1975. The ecological, soft-shelled clam, M a arenaria, at chemical. and histopathological Solomons , Maryland. 35eSamSci . evaluation of an oil s~illsite. 3: 114-120. Part 11. Chem. Stud. ~ar.~ollut: Bull. 6: 166-171. Pf itzenmeyer. H.T. 1965. Annual cycle of gametogenesis of the soft-shelled Munch-Peterson, S. 1973. An clam, Mya arenaria. at Solomons, investiaation of a ~o~ulationof the Maryland. Chesapeake Sci . 6: 52-59. soft ciam (ba arenaria L.) in a Danish estuary. Medd. Dan. Fisk. Pf itzenrneyer, H.T. 1972. Tentative Havunders. (Ser. 3) 7: 47-73. out1 ine for inventory of molluscs: -Mya arenaria (soft-shelled clam). Spear, H.S. 1953. Green crab studies Chesapeake Sci . Suppl . 13: 182-184. at Roothbay Harbor, Maine. Pages 48-52 in- Proc. 4th Annu. Conf. Clam Pf itzenmeyer, H.T., and K.G. Drobeck. Res., Maine Dep. Sea and Shore 1967. Some factors influencing Fish., Boothbay Harbor. reburrowing activity of soft-she1 1 clam, M a arenaria. Chesapeake Sci. Spear, H.S., and J.B. Glude. 1957. 8:193-$59 . Effects of envi ronment and heredity on growth of the soft clam (Mya Pi leggi , J., and B.G. Thompson. 1979. arenaria). U.S. Fish Wildl. Serv. Fisheries of the United States, F3.11. 57: 279-292. 1978. U.S. Natl. Mar. Fish. Serv. Curr. Fish. Stat. 7800. 120 pp. Stanley, S.M. 1970. Relation of shell form to life habits of the bivalvia Ropes, W., and A.P. Stickney. 1965. (Mol lusca) . Geol . Soc. Am. Mem. 125. Reproductive cycle of M a arenaria 296 pp. in New England. Riol. &I.-- Hole) 128: 315-327. Stewart, M.G., and D.R. Bamford. 1976. Absorption of soluble nutrients by Saila, S.B., and T.A. Gaucher. 1966. mid-gut of the bivalve Yya arenaria Estimation of the sampling (L.). J. Molluscan Stud. 42: 63-73. distribution and numerical abundance of some mollusks in a Rhode Island Stickney, A.P. 1964. Feeding and salt pond. Proc. Natl. Shellfish. arowth. . of .iuvenile soft-she1 1 clams, Assoc. 56: 73-80. arena-ria. U.S. Fish. Wildl. Serv., ~ish.-Bull. 63: 635-642. Savage, N. 1981. Soft shell clam studies on the Northern Swan. E.F. 1952. Growth indices of Massachusetts, New Hampshire and the clam M arenaria. Ecology southern Maine coast by Normandeau 33: 365-374. Associates, Inc. Pages 40-57 in 8th Annu. Conf. Clam Res.. Maine D@. of Theroux, R.R., and R.L. Wigley. 1983. Mar. Resour., Roothbay Harbor. Distribution and abundance of east coast bivalve mollusks based on specimens in the National Marine Schubel. J. 1973. Report on the Fisheries Service Woods Hole Maryl and State Department of Health Collection. U.S. Dep. Commer. NOAA, and Mental Hygiene cooperative study Natl. Mar. Fish. Serv., Tech. Rep. to determine cause and extent of 768. 172 pp. high bacteria counts found in M& arenaria in 1973. Mary1 and Turner, H.J., Jr. 1948. Report on Department of Health and Mental investigations of the propagation of Hygiene, Annapolis. 57 pp. the soft-shell clam. Mya arenaria. Woods Hole Oceanogr. Inst. Collected Schuster, C.N., Jr. 1951. On the reprints for 1948. Contrib. 462: 3-9. formation of mid-season checks in the shell of Mya. Anat. Rec. 3: Turner, H.J., Jr. 1953. Growth and 543. survival of soft clams in densely populated areas. Sixth report on Shaw, W .N., and F. Hamnons. 1974. The investigations of the shell- present status of the soft-shell fisheries of Massachusetts, Woods clam in Maryland. U.S. Fish W i 1dl . Hole Oceanogr. Inst. Collected Serv. Spec. Sci. Rep. Fish. No. 508. Reprints for 1953. 195: Contrib. 5 PP. 715: 29-38. van Dam, L. 1935. On the utilization Welch, W.R. 1969. Changes in of oxygen by arenaria. 11. Exp. abundance of the green crab, Carinus Biol. 12: 86-94. maenas (L.), in relation to recent temperature changes. U.S. Fish Wildl. Serv., Fish. Bull. 67: Walker, H.A., . Lorda, and S.R. 337-345. Saila. 1981. A comparison of the inci dence of f i ve path01 ogi cal Welch, W.R., and R. D. Lewis. 1965. conditions in soft shell clams M-'@ Shell movements of Mya arenaria. arenari a from envi ronments with U.S. Rureau of Commercial Fisheries, various pollution histories. Mar. Biological Laboratory, West Boothbay Envi ron. Res. 5: 109-124. Harbor, Maine. Unpubl . Manuscript. REPORT DOCUMENTAiiON 1. =EmRT NO. PAGE ; Biol. Reo. 82(11.53)* 4. Tilla and Subtmtla IRawn 0.1. Species Profiles: Life Histories and Environmental Requirements June. 1986 of Coastal Fishes and Invertebrates (North Atlantic)--Softshell clam - - 7. Adhortsl 6. Parform8n~Organ#zatlon Rept. NO Carter R. Newel 1 and Herbert Hi du 9. Parlonn~n~O~~an#zatlon Nama and Addrass 10. PmlactKashIWorh Unat No. Maine Shel 1fish Research and Development Damariscotta, Maine 04543 and 11. bntractfcl or Crant(C) NO.
Department of Animal and Veterinary Sciences (CI University of Maine, Orono, ME 04469 ,*, 12 sponsor in^ Or~anlzatlonNama and Addrass National Coastal Ecosystems Team U.S. Army Corps of Engineers orn*poflrPar,odCorrnd Fish and Wildlife Service Waterwavs Ex~erimentStation -i U.S. Dep. of the Interior P.O. B& 631' Was hington , DC 20240 Vicksburg, MS 39180
15. Supplem*ntav Hotas *U.S. Army Corps of Engineers Report No. TR EL-82-4
16. Abatncl (Urnit 2W words) The softshell clam, M a arenaria, is a commercially and recreationally important invertebrate that inha 3- itmottom sediments of subtidal and intertidal waters of moderate to high salinity. Its range is 1imited by water temperatures too low for reproduction in the north and by lethal warm temperatures in the south. Clams feed by siphoning seawater and removing food particles, especially phytoplankton, with their gills. Clams are therefore sensitive to factors affecting water qua1 ity, including suspended sediments, sal inity, water temperature, oxygen, and waterborne pollutants. The clam life cycle consists of mass spawning and external ferti 1ization, the development of pelagic larvae, settlement and metamorphosis into spat, and rapid juvenile growth to maturity. Clam recruitment and the migration of spat are dependent upon inshore currents. High morality of eggs, larvae, and spat is largely offset by high reproductive potential. As the clam grows, it finds refuge from most predators deep in the sediments, but it also loses its ability to burrow and is subject to suffocation by siltation. Sediment types, currents, and tidal heights a1 1 affect clam growth rates.
Estuaries Growth Feeding habits Fisheries Sal ini ty Life cycles She1 1fish Temperature Contaminants Sediments Suspended sediments Oxygen b. IdenUlien/Oou+End*d Terms Softshell clam %A arenaria Habitat requirements Spawning
16 Ava~labllityStatement / 19. Sccur8:y Class CThls RIDOR) 1 21. NO. ot Pages I Unl imited I Sea ANS1-239.18) OrTlONAL FORU 212 i4-77) ,~~rrn.rlyN7:S-35' Dcuanrnanr o? r;mmcrre REGION 1 REGION 2 REGION 3 Regional Director Regional Director Regional Director U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service Lloyd Five Hundred Building, Suite 1692 P.O. Box 1306 Federal Building, Fort Snelling 500 N.E. Multnornah Street Albuquerque, New Mexico 87 103 Twin Cities, Minnesota 55 1 1 1 Portland, Oregon 97232
REGION 4 REGION 5 REGION 6 Regional Director Regional Director Regional Director U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service U.S. Fish and Wildlife Service Richard B. Russell Building One Gateway Center P.O. Box 25486 75 Spring Street, S.W. Newton Corner, Massachusetts 02158 Denver Federal Center Atlanta, Georgia 30303 Denver, Colorado 80225
REGION 7 Regional Director U.S. Fish and Wildlife Service 101 1 E. Tudor Road Anchorage, Alaska 99503 DEPARTMENT OF THE INTERIOR U.S. FISH AID WILDLIFE SERVICE
As the Nation's principal conservation agency, the Department of the Interior has respon- sibility 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 as- sesses 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.