|Researched by||Marisa Sabatini||Refereed by||This information is not refereed.|
|Other common names||-||Synonyms||-|
- none -
|Phylum||Mollusca||Snails, slugs, mussels, cockles, clams & squid|
|Class||Bivalvia||Clams, cockles, mussels, oysters, and scallops|
|Typical abundance||High density|
|Male size range||<5cm|
|Male size at maturity||~2.5cm|
|Female size range||~2.5cm|
|Female size at maturity|
|Growth rate||See additional information|
|Body flexibility||None (less than 10 degrees)|
|Characteristic feeding method||Active suspension feeder, Active suspension feeder|
|Typically feeds on||Phytoplankton (i.e. diatoms)|
|Dependency||No information found.|
|Supports||No information found|
|Is the species harmful?||No|
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).
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).
|Physiographic preferences||Open coast, Offshore seabed, Strait / sound|
|Biological zone preferences||Lower eulittoral, Lower infralittoral, Sublittoral fringe, Upper infralittoral|
|Substratum / habitat preferences||Fine clean sand, Gravel / shingle, Mixed, Pebbles|
|Tidal strength preferences||Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Weak < 1 knot (<0.5 m/sec.)|
|Wave exposure preferences||Exposed, Moderately exposed, Sheltered, Very exposed|
|Salinity preferences||Full (30-40 psu)|
|Depth range||5-50 m|
|Other preferences||No text entered|
|Migration Pattern||Non-migratory / resident|
|Reproductive type||Gonochoristic (dioecious)|
|Reproductive frequency||Annual protracted|
|Fecundity (number of eggs)||No information|
|Generation time||Insufficient information|
|Age at maturity||1 year|
|Season||February - June|
|Life span||5-10 years|
|Duration of larval stage||No information|
|Larval dispersal potential||See additional information|
|Larval settlement period||Insufficient information|
This MarLIN sensitivity assessment has been superseded by the MarESA approach to sensitivity assessment. MarLIN assessments used an approach that has now been modified to reflect the most recent conservation imperatives and terminology and are due to be updated by 2016/17.
|Removal of the substratum would also remove the entire population of Spisula solida and so intolerance has been assessed as high with a high recoverability.|
|Spisula solida is a fast burrowing bivalve. If Spisula solida were covered by sediments it would be able to reposition itself within the sediment. The location of the Waterford clam bed (Ireland) was examined in 2001. Fishermen compared the areas of the clam bed that provided the heaviest catches in two years. It was concluded that the location of the heaviest catches had moved slightly to the north-west of the harbour as part of the existing bed had silted up. This reduced the numbers of Spisula solida and the size of the clam patch (Fahy et al., 2003). However, intolerance has been assessed as intermediate to reflect the reduction in the size of the clam bed and Spisula numbers. Recoverability is assessed as high.|
|Low||Very high||Very Low||Very low|
|Levels of suspended sediment are likely to be most relevant to feeding. An increase in suspended sediment is likely to increase the rate of siltation (see smothering above) and the availability of food as Spisula solida is a suspension feeder. However, if the level of suspended sediment become too high it could cause the feeding structures to become clogged. It is unlikely that mortality would occur, therefore intolerance has been assessed as low with a very high recoverability.|
|Levels of suspended sediment are likely to be most relevant to feeding. A decrease in suspended sediment is likely to decrease the availability of food for suspension feeding bivalves. Mortality is unlikely to occur within 1 month (see benchmark) and so intolerance is assessed as low. When suspended sediment levels return to normal, so too should food availability and feeding.|
|Spisula solida can be found occasionally in the intertidal. A change in desiccation at the benchmark level would affect Spisula solida at the upper limit of their distribution and may cause mortalities. Therefore intolerance is assessed as intermediate with a high recoverability.|
|An increase in emergence at the benchmark level, would most likely to reduce the upper limits of Spisula solida and a portion of the population may be lost. Therefore intolerance is assessed as intermediate with high recoverability a recoverability.|
|Tolerant*||Not relevant||Not sensitive*|
|A decrease in emergence at the benchmark level would benefit individuals ofSpisula solida allowing them to colonize further up the shoreline. Therefore, Spisula solida is tolerant* of this factor.|
|Spisula solida is found in areas ranging from strong to weak water flow. The increased water flow rate at the benchmark level would change the sediment characteristics in which the species lives. The substrata may be disturbed and the sediment on the seabed may erode. This scouring of sand and gravel causes coarse sediments to become unstable and difficult to burrow. Additionally, an increase in water flow may interfere with feeding and respiration.
Increased water flow may also lead to the dislodgement and abrasion of Spisula solida. However, the worn appearance of Spisula solida shells indicate that they inhabit areas of considerable water movement. A proportion of the population of Spisula solida may also be transported to another position on the seabed (bedload transport). Increased water flow may also prevent the settlement of larvae and juveniles decreasing the recruitment to an area (Hiscock, 1983). Therefore intolerance is assessed as intermediate with a high recoverability.
|Spisula solida is found in areas ranging from strong to weak water flow. A decreased water flow rate may lower the dispersion of planktonic larvae and recruitment from other areas would be minimal. A decrease in water flow at the benchmark level would also result in increased deposition of fine suspended sediment (Hiscock, 1983), changing the sediment characteristics of the habitat in which the species lives. This may cause the substratum to become too muddy for Spisula solida which prefers sandy sediments and mixed sediments and avoids muddy sediments. Some mortality is, therefore, expected and an intolerance of intermediate is recorded. Recoverability is assessed as high|
|Tolerant||Not relevant||Not sensitive||Low|
|Schlieper et al. (1967) state that the upper temperature tolerance of Spisula solida is 30°C. Fahy et al. (2003) stated that the optimum condition of Spisula solida occurred at low temperature. However, Spisula solida does occur in areas as far south as Portugal and Morocco and is unlikely to be affected by an increases in temperature experienced in British and Irish waters. Therefore, Spisula solida would probably be tolerant of an increase in temperature at the benchmark level.|
|Fahy et al. (2003) stated that the optimum condition of Spisula solida occurred at low temperatures. Spisula solida also occurs as far north as sub-arctic Iceland and Norway. Therefore, Spisula solida would probably be tolerant of an increase in temperature at the benchmark level. However, the Spisula solida population of Red Wharf Bay, Anglesey was reported to demonstrate 'exceptionally heavy mortality' as a result of the 1962/63 winter (Crisp, 1964). Futhermore, the clam disappeared from the entire German Bight above the 20 m depth contour line during the 1995/96 winter where water temperatures at the sea bottom dropped to 0°C (M. Ruth, pers. comm.). Therefore, Spisula solida is probably highly intolerant of an acute temperature change, at the benchmark level.|
|Low||Very high||Very Low||Low|
|Spisula solida does not require light and therefore the effects of increased turbidity on light attenuation are not directly relevant. An increase in turbidity may affect primary production in the water column and therefore reduce the availability of food. A turbidity increase for a year (see benchmark) would reduce the availability of food that would probably affect growth and fecundity and an intolerance of low is recorded. As soon as light levels return to normal, primary production will increase and hence recoverability is recorded as very high.|
|Tolerant||Not relevant||Not sensitive||Low|
|Spisula solida does not require light and therefore the effects of increased turbidity on light attenuation are not directly relevant. A decrease in turbidity would increase primary production in the water column and food availability. Therefore it is likely that Spisula solida would be tolerant of a decrease in turbidity.|
|Spisula solida occurs in wave exposed to wave sheltered areas. This suggests that the species would be tolerant of a certain degree of sediment mobility associated with strong wave action. An increase in wave exposure (at the benchmark level) would place the majority of the population in areas frequently subject to strong wave action and the species may be affected in several ways. Strong wave action may cause damage or withdrawal of the siphons, resulting in loss of feeding opportunities and compromised growth. Furthermore, individuals may be dislodged by scouring from sand and gravel mobilized by increased wave action. Breon (1970; cited in Chícharo et al., 2002) reported that Spisula subtruncata, a species with a depth distribution similar to Spisula solida, exhibited increased burrowing activity when disturbed by wave action. Therefore intolerance is assessed as intermediate with a high recoverability.|
|Spisula solida occurs in wave exposed to wave sheltered areas. Decreased wave exposure at the benchmark level is likely to result in the establishment of more stable muddy sediment habitats. It is likely that this would result in mortality of Spisula solida. Spisula solida may also probably suffer increased competition from species better adapted to life in low energy environments. Intolerance is therefore assessed as intermediate with a high recoverability.|
|No information||Not relevant||No information||Low|
|No information was found concerning the effects of noise on Spisula solida.|
|No information||Not relevant||No information||Low|
|Spisula solida probably has little visual acuity and has been recorded as not sensitive to this factor.|
|The worn appearance of Spisula solida shells indicate that they inhabit areas of considerable water movement showing some tolerance for the effects of water movement on their robust shells (Ford, 1925). |
Fishing for demersal species will disturb the surface layer of sediment and any protruding or shallow burrowing species. In Portugal, Spisula solida is caught at a depth of 7-9 m with a tooth dredge that can penetrate the sediment to a depth of 50 cm. Gaspar et al. (2002) noted that 93% of the uncaught Spisula solida were undamaged after experimental trawls, as they were well protected by their thick shells, and only 1% of the uncaught Spisula solida died (Gaspar et al., 2002).
The impacts caused by a fishing dredge significantly increased the number of exposed Spisula solida clams and the abundance of potential predators (Chícharo et al., 2002). The impact of the dredge increased the time needed for Spisula solida to rebury, which rendered them vulnerable to predation for longer periods (Chícharo et al., 2002). Under controlled conditions, it took Spisula solida three minutes to rebury themselves when displaced to the surface. However under trawling/dredging conditions it took Spisula solida nine minutes to rebury back into the sediments (Chícharo et al., 2002). Chícharo et al. (2002) stated that only 6% of Spisula solida not caught by the dredge were damaged and 94% were classified as having none or slight damage. Therefore intolerance has been assessed as intermediate as mortality may occur and recoverability has been assessed as high.
|Spisula solida can burrow back down into the sediment very rapidly in its preferred substrata when it is displaced to the surface, therefore it is probably relatively tolerant of displacement. Spisula solida are subject to considerable water movements that cause displacement, which can carry individuals to another position where they will once again settle (Ford, 1925). This can be seen when different morphologies of Spisula solida occur in the same area. It is unlikely that mortalities will occur as Spisula solida has a thick solid shell and individual Spisula solida are often found with a worn appearance that is consistent with such activity (Ford, 1925).
The impacts caused by a fishing dredge significantly increased the number of exposed Spisula solida clams and the abundance of potential predators (Chícharo et al., 2002). The impact of the dredge increased the time needed for Spisula solida to rebury and rendered them vulnerable to predation for longer periods (Chícharo et al., 2002). Under controlled conditions it took Spisula solida three minutes to rebury when displaced however under trawling/dredging conditions it took Spisula solida nine minutes to rebury back into the sediments (Chícharo et al., 2002).
However such displacement could result in a loss of recruitment, increased predation and loss of mature individuals which will affect the viability of a population. Therefore intolerance is assessed as intermediate with a high recoverability.
|Effects of synthetic contamination on bivalves are listed below.
|Many bivalve species accumulate heavy metals in their tissues, far in excess of environmental levels. Examples of the sub-lethal effects of heavy metals include: siphon retraction, valve closure, inhibition of byssal thread production, disruption of burrowing behaviour, inhibition of respiration, inhibition of filtration rate, inhibition of protein synthesis and suppressed growth (see review by Aberkali & Trueman, 1985). Bryan (1984), suggested that Hg was the most toxic metal to bivalve molluscs in experimental studies while copper (Cu), cadmium (Cd) and zinc (Zn) were the most problematic for bivalves in the field. For example:
|The effects of oil on invertebrate molluscs include:|
|No information||Not relevant||No information||Not relevant|
|No information was found on the effects of radionuclides on Spisula solida.|
|Increased nutrients are likely to enhance ephemeral algal and phytoplankton growth, increase organic material deposition and enhance bacterial growth. At low levels, an increase in phytoplankton may increase food availability for Spisula solida. However, increased levels of nutrients (beyond the carrying capacity of the environment) may result in eutrophication, algal blooms and reductions in oxygen concentrations that can cause hypoxia. Rosenberg & Loo (1988) reported mass mortalities of the bivalves Mya arenaria and Cerastoderma edule following a eutrophication event in Sweden, however no direct causal link was established. Spisula sp. were reported to accumulate algal toxins (e.g. saxitoxin and neosaxitoxin) in their tissues, and to retain toxins for long periods of time, ranging from months to over three years (see review by Landsberg, 1996). However, Landsberg (1996) found no evidence of resultant neoplasias (cancers) in Spisula sp. and did not report evidence of mortalities in Spisula sp. induced by algal blooms. However, Mahoney & Steimle (1979) reported mass mortalities of Spisula solidissima off the coast of New Jersey, due to of bottom water oxygen deficiency, as a result of the decay of a bloom of the dinoflagellate Ceratium tripos (see oxygenation below). Therefore, while Spisula sp. May be relatively tolerant of algal toxins, algal blooms may indirectly cause mortality due to hypoxia. Therefore, a dramatic increase in nutrient levels may cause some mortality of Spisula solida, and an intolerance of intermediate has been reported.|
|Spisula solida is typically found in full salinity conditions. Spisula solida exhibited the lowest salinity tolerance of excised gill tissues compared to the other species tested. After 24 hours, ciliary activity of 4 to 8 mm² gill pieces was observed in salinities that ranged from 15 to 50 parts per thousand (Theede, 1965; reported in Kinne, 1971b). The whole animal is likely to tolerate changes in salinity for longer, since it can isolate itself from its surroundings by closing its valves. However, at the benchmark level, an acute change for a period of 1 week or a chronic change for a year is likely to result in mortality. Therefore, an intolerance of high has been recorded.|
|Spisula solida exhibited the lowest salinity tolerance of excised gill tissues compared to the other species tested. After 24 hours, ciliary activity of 4 to 8 mm² gill pieces was observed in salinities that ranged from 15 to 50 parts per thousand (Kinne, 1971b). The whole animal is likely to tolerate changes in salinity for longer, since it can isolate itself from its surroundings by closing its valves. Spisula solida is typically found at full salinities (Theede et al., 1969) and is likely to be intolerant of a decrease in salinity. Distributionally, Spisula solida extends into the Kattegat (Sweden) but does not enter the brackish waters of the Baltic Sea as the salinity is lower (Theede et al., 1969). At the benchmark level, an acute change for a period of 1 week or a chronic change for a year is likely to result in mortality. Therefore intolerance has been assessed to be high with a high recoverability.|
|Diaz & Rosenberg (1995) list Spisula solida as sensitive to hypoxic events. Spisula solida exhibited the fastest declines in ciliary movement in excised gill tissue, compared to other species tested at oxygen concentrations of 0.21 mg/l (Theede at al., 1969). Excised gill tissues of Spisula solida showed irreversible damage after 4 days under anoxic conditions after which ciliary movement completely stopped. The tolerance of the whole animal is likely to be longer, since it can shut itself off from the surrounding water by closing its valves.|
Decay of an immense bloom of the dinoflagellate Ceratium tripos caused severe hypoxia over a 13,000 km² in the New York bight in 1976 (Mahoney & Steimle, 1979). The oxygen levels dropped 2ml/l (2.8 mg/l) over a wide area, and to as low as 0.1 ml/l (0.14 mg/l) in the worst affected areas, with an associated increase in hydrogen sulphide levels. Spisula solidissima was the most affected species and exhibited an estimated 69% mortality (Mahoney & Steimle, 1979). Overall, the above evidence suggests that Spisula solida and related species are relatively intolerant of hypoxic conditions. Therefore, a change in oxygenation at the benchmark level would probably cause the population of Spisula solida to collapse and recoverability would be reliant on outside recruitment. Therefore intolerance is assessed as high with a high recoverability.
|A number of organisms have been found living on and in individual specimens of Spisula solida.
|No information||Not relevant||No information||Low|
|There is no information on the effects of non-native species on Spisula solida.|
|Spisula solida is fished commercially. The impacts caused by a fishing dredge significantly increased the number of exposed Spisula solida clams and the abundance of potential predators (Chícharo et al., 2002). The impact of the dredge increased the time needed for Spisula solida individuals to rebury rendering them vulnerable to predation for longer.
Since 1992 a fishery for Spisula solida has taken place in Danish waters. Catches and landings were high in some years but totally absent in others during a ten year fishing period between 1992 and 2002 (Jensen et al., 2003). From 1992 to 1995 the fishery continued without any decrease in cpue (M. Ruth, pers. comm.). However, Spisula solida disappeared from the entire German Bight above the 20 m depth contour line during the 1995/96 winter where water temperatures at the sea bottom dropped to 0°C (M. Ruth, pers. comm.). 1995 also saw the fishery ending due to bad weather conditions (M. Ruth, pers. comm.). In April 1996, when the fishery tried to start again, no living Spisula solida were found (M. Ruth, pers. comm.). The suction dredging gear was subsequently modified to access Spisula solida living at greater depths.Because the clams are fished commercially, at least some of the population will be removed and, therefore, intolerance has been assessed as intermediate. Even if the clams are not caught, the dredging will at the very least leave the clams more susceptible to predation. Recoverability will probably be high.
|No specific information was found concerning the effects of the extraction of other species on Spisula solida. Any extraction of other species using fishing gear that penetrates the seabed such as scallop dredging is likely to cause forced disturbances (as above) or remove species as bycatch. Therefore intolerance has been assessed as intermediate with a high recoverability.|
- no data -
|National (GB) importance||-||Global red list (IUCN) category||-|
European Union regulations
A minimum size limited of 2.5 cm for Spisula solida clams was imposed by European Union Council Regulation 850/98, Annex XII (Fahy et al., 2003). However Fahy et al. (2003) suggested that bars on a clam dredge should be a minimum 11 mm apart, which corresponds to an age of three years.
Commercial fishing methods screen Spisula catches so that the smaller and younger individuals are not retained by the dredge (Fahy et al., 2003). The largest of certain medium age groups will be retained and probably the oldest groups are representative of the size range within the population (Fahy et al., 2003). Spisula solida is harvested in Waterford Harbour (Ireland). The harvesting of Spisula solida was irregular and sporadic as the principle dealers landed 400 tonnes of Spisula solida in 1996, no landings were traced from 1997 or 1998 and only 6 tonnes was harvested in 1999 (Fahy et al., 2003). In 2000, 338 tonnes of Spisula solida was landed, however, in the following two years the numbers of Spisula solida dropped further as the calm bed started to become barren (Fahy et al., 2003). Kristensen (1996) stated that a biomass of less than 200 g/m2 was not considered worth fishing. Kristensen (1996) also suggested that an exploitation rate should range from 10-15%. Fahy et al. (2003) suggested likely that the above exploitation rate of Spisula solida was exceeded whenever surf clam patches were harvested in Ireland.
Spisula solida is an important component of the diet of many flat fishes.
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This review can be cited as:
Last Updated: 31/05/2007