BIOTIC

BIOTIC Species Information for Spisula solida

Researched by

Lizzie Tyler

Data supplied by

University of Sheffield

Refereed by

This information is not refereed.

Taxonomy

Scientific name

Spisula solida

Common name

Thick trough shell

MCS Code

W1977

Recent Synonyms

None

Phylum

Mollusca

Subphylum

Superclass

Class

Pelecypoda

Subclass

Order

Veneroida

Suborder

Family

Mactridae

Genus

Spisula

Species

solida

Subspecies

Additional Information

Spisula 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 form

Bivalved

Feeding method

Passive suspension feeder
Active suspension feeder

Mobility/Movement

Crawler
Burrower

Environmental position

Infaunal

Typical food types

Phytoplankton (i.e. diatoms)

Habit

Burrow dwelling

Bioturbator

Flexibility

None (< 10 degrees)

Fragility

Intermediate

Size

Small-medium(3-10cm)

Height

Insufficient information

Growth Rate

See additional information

Adult dispersal potential

100-1000m

Dependency

Independent

Sociability

Solitary

Toxic/Poisonous?

General Biology Additional Information

Abundance 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).

Growth
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 & Ireland

Recorded at scattered locations around the coasts of Britain and Ireland.

Global distribution

Spisula solida is distributed from subarctic Iceland and Norway as far south as Portugal and Morocco but is not found in the Mediterranean.

Biogeographic range

Not researched

Depth range

Migratory

Non-migratory / Resident

Distribution Additional Information

Kristensen (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 preferences

Mixed
Pebbles
Gravel / shingle
Fine clean sand

Physiographic preferences

Open coast
Offshore seabed
Strait / sound

Biological zone

Lower Eulittoral
Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral

Wave exposure

Very Exposed
Exposed
Moderately Exposed
Sheltered

Tidal stream strength/Water flow

Strong (3-6 kn)
Moderately Strong (1-3 kn)
Weak (<1 kn)

Salinity

Full (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 type

Gonochoristic

Developmental mechanism

Planktotrophic

Reproductive Season

February to June

Reproductive Location

Insufficient information

Reproductive frequency

Annual protracted

Regeneration potential

Life span

6-10 years

Age at reproductive maturity

1 year

Generation time

Insufficient information

Fecundity

Egg/propagule size

Fertilization type

Insufficient information

Larvae/Juveniles
Larval/Juvenile dispersal potential	Insufficient information	Larval settlement period	Insufficient information
Duration of larval stage

Reproduction Preferences Additional Information

Longevity
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).

Gametogenesis
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
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).
Dispersal
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).
Recruitment
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,