BIOTIC Species Information for Spisula solida
Researched byLizzie Tyler Data supplied byUniversity of Sheffield
Refereed byThis information is not refereed.
Scientific nameSpisula solida Common nameThick trough shell
MCS CodeW1977 Recent SynonymsNone

PhylumMollusca Subphylum
Superclass ClassPelecypoda
Subclass OrderVeneroida
Suborder FamilyMactridae
GenusSpisula Speciessolida

Additional InformationSpisula solida may be confused with Spisula elliptica, however the latter is smaller and more delicate. Spisula elliptica is also narrower relative to its length. Spisula solida may also be confused with Mactra stultorum but the cardinal teeth of the latter are smooth rather than ridged. Please note: the biology of Spisula solida is poorly known and information on closely related species has been used where appropriate.
Taxonomy References Howson & Picton, 1997, Tebble, 1976, Gibson et al., 2001, Fish & Fish, 1996,
General Biology
Growth formBivalved
Feeding methodPassive suspension feeder
Active suspension feeder
Environmental positionInfaunal
Typical food typesPhytoplankton (i.e. diatoms) HabitBurrow dwelling
Bioturbator FlexibilityNone (< 10 degrees)
FragilityIntermediate SizeSmall-medium(3-10cm)
HeightInsufficient information Growth RateSee additional information
Adult dispersal potential100-1000m DependencyIndependent
General Biology Additional InformationAbundance and biomass
The abundance of Spisula solida varies with location. For example, the following abundances and biomass were reported:
  • 0-240 ind./m² (0-2046 g/m²) at Røde Klit Sand (Denmark) (Kristensen, 1996);
  • 0-45 ind./m² (0-632 g/m²) at Horns Reef (Denmark) (Kristensen, 1996); whereas
  • 2000 ind./m2in Start Bay (UK) (Ford, 1925).
In Danish waters the average biomass of Spisula solida was 265 g/m² in the Røde Klit Sand 103 g/m² at Horns Reef (Kristensen, 1996). In Waterford Harbour, (Ireland) the maximum biomass was 600 g/m2 (Fahy et al., 2003).

The growth of Spisula solida is rapid during its first two years and then slows down (Gaspar et al., 1995; Kristensen, 1996). This rapid increase in size was reported in Waterford Harbour where the number of Spisula solida per kg declined rapidly between the ages of 2-3 (769 - 227 ind./kg) (Fahy et al., 2003). Over the following three years this figure halved again to 101 ind./kg (Fahy et al., 2003).

Growth can be influenced by environmental factors, particularly density. For instance, Weinberg & Hesler (1996) compared growth curves of Spisula solidissima in two areas off the New Jersey and Dekmarva coasts (U.S.) and the Long Island and South New England coasts (U.S.) following a hypoxic event, which resulted in mortalities in the southernmost in 1976. Both growth and maximum shell length declined in Long Island/South New England, whereas in New Jersey/Dekmarva growth and shell length remained constant and had not been affected by the hypoxia. Weinberg & Hesler (1996) suggested that following the hypoxia, the first clams to recolonize grew more rapidly in the presence of a good food supply and without competitors.

Growth rates
Clear shell sculpture marks occur on Spisula solida, suggesting annual rings, but their interpretation is not straight forward (Fahy et al., 2003). The shell surface of Spisula solida also exhibits some disturbance lines, that are impossible to distinguish from annual growth lines therefore internal bands are used (Gaspar et al., 1995). Taylor et al. (1969,1973; cited in Fahy et al., 2003) described the shells of the superfamily Mactracea. Their shells are composed of two layers of aragonite: a white, opaque, outer layer, consisting of crossed lamellar crystalline structure, which is separated by the pallial myostracum from a grey, somewhat translucent, inner layer. The white outer shell layer and the chondrophore are streaked periodically with dark lines (internal growth lines). This structure confirms the presence of true annuli, which external sculpture alone might not indicate. During winter, wide growth increments are deposited, which is characteristic of rapid shell growth whilst narrow spaced dark zones are formed in summer (Gaspar et al., 1995).

The maximum length of Spisula solida (5 cm) from Irish waters is similar to that of northern European stocks but growth rates appear to vary geographically. Dimensions attained by Irish Spisula solida differ from those reported from other northern European stocks of the species. In the Danish North Sea, individuals between 2-3 years reached a length of 35 mm. Meixner (1994; cited in Fahy et al., 2003) reported that Spisula solida 35 mm in length from the German North Sea similarly averaged 2.5 years old while in Waterford Harbour individuals were 5.27 years at the same length (Fahy et al., 2003).

Biology References Kristensen, 1996, Ford, 1925, Gaspar et al.,1995, Weinberg & Helser, 1996, Hayward & Ryland, 1990,
Distribution and Habitat
Distribution in Britain & IrelandRecorded at scattered locations around the coasts of Britain and Ireland.
Global distributionSpisula solida is distributed from subarctic Iceland and Norway as far south as Portugal and Morocco but is not found in the Mediterranean.
Biogeographic rangeNot researched Depth range
MigratoryNon-migratory / Resident   
Distribution Additional InformationKristensen (1996) reported that Spisula solida showed a preference for grain sizes that ranged between 2-3 mm. The population of Spisula solida in Waterford Harbour, (Ireland) conformed to the grain size preference above. Spisula solida can be found at depths of 50 m (Schlieper et al., 1967). But in the North Sea, Spisula solida is restricted to depths of about 10-15 m (Theede et al., 1969). Whereas, in Portuguese waters, Spisula solida is more common in greater abundances at depths between 5-13 metres (Gaspar et al., 1999).

Substratum preferencesMixed
Gravel / shingle
Fine clean sand
Physiographic preferencesOpen coast
Offshore seabed
Strait / sound
Biological zoneLower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Wave exposureVery Exposed
Moderately Exposed
Tidal stream strength/Water flowStrong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Tebble, 1976, Gibson et al., 2001, NBN, 2002, Picton & Costello, 1998, JNCC, 1999, Theede et al., 1969, Schlieper et al., 1967, Hayward & Ryland, 1990,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismPlanktotrophic
Reproductive SeasonFebruary to June Reproductive LocationInsufficient information
Reproductive frequencyAnnual protracted Regeneration potential No
Life span6-10 years Age at reproductive maturity1 year
Generation timeInsufficient information Fecundity
Egg/propagule size Fertilization typeInsufficient information
Larval/Juvenile dispersal potentialInsufficient information Larval settlement periodInsufficient information
Duration of larval stage   
Reproduction Preferences Additional InformationLongevity
The life expectancy of Spisula solida is up to approximately ten years (Fahy, 2003).

Sexual maturity
Spisula solida reaches sexual maturity during its first year, which is a function of age, not of size (Gaspar & Monteiro,1999; Fahy et al., 2003).

The sexes of Spisula solida are separate and there are no records of hermaphrodites (Gaspar & Monteiro, 1999). Male and female white clams are distinguishable externally since the colour of the gonad in this species is reddish in the females and yellowish-orange in the males (Gaspar & Monteiro, 1999). Both sexes show a synchrony in gametogenic development and spawning.

Gaspar & Monteiro (1999) observed that gametogenesis in Spisula solida began when the seawater temperature started to decrease (late September). Gaspar et al. (1999) concluded that the initiation of gametogenesis in Spisula solida was a response to falling temperature and that spawning occurred when the temperature began to rise rather than occurring at a fixed temperature. The maturation of the gonad continued until late January when the water temperature was at its lowest (Gaspar & Monteiro, 1999). In Danish waters specimens of Spisula solida were sexually inactive from July-Sept. The first ripe stage of gonads was reached in December, and all individuals were ripe by January (Gaspar & Monteiro, 1999).

Spawning begins in February (Gaspar & Monteiro, 1999). Gaspar & Monteiro (1999) noted that 75% of a studied population were in the spent stage of their gametogenic cycle by June (Gaspar & Monteiro, 1999).
Ford (1925) suggested that Spisula solida can be moved along by water movement (bed load transport) along the sea bottom to another position on the seabed. Therefore, in the course of time considerable mixing could easily bring together individuals of different ages and origins (Ford, 1925).
In Ireland the recruitment of Spisula solida is irregular with 1 year old clams out numbering all the other year classes (Fahy et al., 2003). The reasons for this are unknown. However, irregular settlement rather than erratic gamete production might be the explanation for the occasional strong representation of a year class in Waterford Harbour clam population (Fahy, 2003).
Reproduction References Gaspar & Monteiro, 1999, Ford, 1925, Fahy, 2003, Fahy et al., 2003,
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