BIOTIC Species Information for Abra alba
Click here to view the MarLIN Key Information Review for Abra alba
Researched byLizzie Tyler Data supplied byUniversity of Sheffield
Refereed byThis information is not refereed.
Taxonomy
Scientific nameAbra alba Common nameWhite furrow shell
MCS CodeW2059 Recent SynonymsNone

PhylumMollusca Subphylum
Superclass ClassPelecypoda
Subclass OrderVeneroida
Suborder FamilySemelidae
GenusAbra Speciesalba
Subspecies   

Additional InformationAbra alba may also be known as the 'white furrow shell' (Rees & Dare, 1993).
Taxonomy References Howson & Picton, 1997, Tebble, 1976, Hayward & Ryland, 1995b, Rees & Dare, 1993,
General Biology
Growth formBivalved
Feeding methodPassive suspension feeder
Active suspension feeder
Surface deposit feeder
Sub-surface deposit feeder
Mobility/MovementBurrower
Environmental positionInfaunal
Typical food typesPhytoplankton, detritus. HabitBurrow dwelling
Bioturbator FlexibilityNone (< 10 degrees)
FragilityIntermediate SizeSmall(1-2cm)
HeightInsufficient information Growth Rate0.1 mm/day
Adult dispersal potential100-1000m DependencyIndependent
SociabilitySolitary
Toxic/Poisonous?No
General Biology Additional InformationAbundance
Although described as solitary animals, adult densities may exceed 1,000 m² in favourable conditions. For instance, in the rich organic muddy harbour sediments in the Ria de la Coruna (NW Spain) Abra alba densities varied from 97 to 2,939 individuals/ m² (Francesch & Lopez-Jamar, 1991). In front of Dunkirk, France, densities can reach 9,000 individuals / m² (Ghertsos et al., 2000). However, abundances typically fluctuate between years owing to variation in recruitment success (juvenile bivalves experience high mortality within the first month after settlement) or adult mortality. High densities of newly settled spat have been reported. For instance, estimated densities of between 16,000 - 22,000 individuals/ m² (collected on 1 mm sieves) were recorded by Jensen (1988) at the time of settlement in the western part of the Limfjord, Denmark.

Growth
The smallest recorded benthic specimen had a shell length of 0.34 mm (Dauvin & Gentil, 1989). In autumn settled spat growth is insignificant until spring when a maximum growth rate of 0.1 mm/day was reported (Dauvin, 1986). This growth rate applies from spring to autumn (Dauvin, pers. comm.).

Nutrition
Some bivalves, such as Abra alba, which inhabit muddy low energy environments can switch back and forth from suspension feeding and deposit feeding, depending upon the conditions of the environment (Dame, 1996). While suspension feeding, the inhalant siphon is held a few millimetres above the sediment surface and sucks in suspended particles. For instance, Abra alba significantly reduced the concentration of the flagellate Isochrysis galbana in suspension. Consumption of Isochrysis galbana over four hours was estimated to be 2.7% of the body weight (Rosenberg, 1993). While deposit feeding, the inhalant siphon is bent over toward the sediment surface, sucking up detritus. However, as the food quality of sediments is often low, deposit feeders either have to process large volumes of sediment through the digestive tract in order to gain a small amount of nutrition, or they sort particles before ingestion and reject the majority of particles as pseudofaeces. As a result the feeding rate is lower with a longer residence time for food in the gut, enabling digestion of the more complex organic compounds common to the benthic environment (Dame, 1996).

Biomass and productivity
In Kiel Bay, mean annual biomass varied greatly between sites and between years: Biomass (B) =0.1-3 g AFDW m², with a long-term average (ratio) P:B = c 2.2 (Rainer, 1985); B = 0.1-2 g AFDW m² and P:B = 1.7-2.9 from five years of sampling at a location off the French coast (Dauvin, 1986); B = 0.3 g AFDW m² and P:B = 1.4 in the Bristol Channel, England (Warwick & George, 1980).
Biology References Nott, 1980, Allen, 1983, Dauvin, 1982, Dauvin & Gentil, 1989, Dame, 1996, Rosenberg, 1993, Francesch & Lopez-Jamar, 1991, Jensen, 1988, Rees & Dare, 1993, Rainer, 1985, Dauvin, 1986, Warwick & George, 1980, Ghertsos et al., 2000,
Distribution and Habitat
Distribution in Britain & IrelandWidespread around the British Isles.
Global distributionAbra alba is distributed from the Norwegian Sea and the Baltic, south to the Iberian Peninsula, into the Mediterranean and Black Seas, and south along the coast of Africa to Senegal.
Biogeographic rangeNot researched Depth range0 - 60 m
MigratoryNon-migratory / Resident   
Distribution Additional InformationDispersal of post-larval bivalve molluscs
The mechanism termed 'byssus drifting' has been observed in 20 species of bivalve molluscs, including Abra alba, and is the mechanism by which post-larval bivalves enter a second pelagic migratory stage. Young bivalves secrete a single, long thread which increases the drag acting upon them and enables them to be carried along on the current. The drag increase was found to be a factor of 3 to 30 times greater on byssus secreting bivalves than on inactive ones (Sigurdsson et al., 1976). Abra alba were observed to re-enter the water column after larval settlement in the Bay of Seine (Olivier et al., 1996). The post-larvae and juveniles of Abra alba were most abundant at flood tide velocities . Furthermore, Abra alba were found to vary significantly in their vertical distribution in the water column, the species decreasing in abundance with distance from the sea bed. It was noted that Abra alba juveniles can regulate their vertical position in the flow, to some extent, by opening their valves to different extents (Olivier et al., 1996).

Substratum preferencesMuddy gravel
Sandy mud
Mud
Muddy sand
Physiographic preferencesOpen coast
Offshore seabed
Strait / sound
Sealoch
Enclosed coast / Embayment
Biological zoneSublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral
Wave exposureSheltered
Tidal stream strength/Water flowWeak (<1 kn)
SalinityFull (30-40 psu)
Habitat Preferences Additional Information
Distribution References Tebble, 1976, Sigurdsson et al., 1976, JNCC, 1999, NBN, 2002, Picton & Costello, 1998, Olivier et al., 1996,
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismPlanktotrophic
Reproductive SeasonFebruary to Autumn Reproductive LocationWater column
Reproductive frequencyAnnual protracted Regeneration potential No
Life span1-2 years Age at reproductive maturity
Generation time<1 year Fecundity17000
Egg/propagule size60 µm diameter Fertilization typeExternal
Larvae/Juveniles
Larval/Juvenile dispersal potential>10km Larval settlement periodInsufficient information
Duration of larval stage1-2 months   
Reproduction Preferences Additional InformationGametogenesis
Dewarumez (1979) and Nott (1980) described the anatomy of the gonads of Abra alba and changes in the gonad condition during the reproductive cycle.

Fertilization and metamorphosis
The sexes are separate and may be distinguished microscopically by dissection. Nott (1980) estimated the number of eggs produced from an average sized animal 11 mm in length to be between 15,000 - 17,000 of 60 µm diameter. Gametes are shed within the shell cavity and swept out through the exhalent siphon by pumping, so that fertilization occurs externally. The eggs develop into free-swimming trochophore and then veliger larvae. The larval stage is planktonic, and in Abra alba, lasts about a month (Dauvin & Gentil, 1989). Larvae are subject to very high mortality. At metamorphosis, the larvae settle out of the plankton and the bivalve spends its remaining life as a member of the benthos (Dame, 1996).

Recruitment
Recruitment varies between localities. In a population of Abra alba from the Irish Sea, proliferation of the gonads commenced in March and the animals reached maturity between June and September. The exact time at which maturity was attained depended upon the size of the individual, but it seemed that only individuals with a minimum shell length of between 7-9 mm reproduced (Nott, 1980). Normally, there two distinct spawning periods in summer and autumn, and according to the season of settlement, individuals differ in terms of growth and potential life span. Although peak recruitment usually occurs in summer (Dauvin & Gentil, 1989).
  • In Kiel Bay a recruitment peak occurred in August, sometimes with a second peak between December and February (Rainer, 1985).
  • Autumn settled individuals from the Bay of Morlaix, France, initially showed no significant growth; they were not collected on a 1 mm mesh sieve until April, 5 to 7 months after settlement. Such individuals were expected to have a maximum life span of 21 months and could produce two spawnings. In contrast, veliger larvae that settled during the summer grew very rapidly and were collected on a 1 mm mesh sieve just one month after settlement. They lived about one year and spawned only once (Dauvin & Gentil, 1989).
  • Dauvin & Gentil (1989) observed three recruitment periods (February-March, April-June and August-October) in response to trophic conditions following the Amoco Cadiz oil spill in the Bay of Morlaix, France (see sensitivity, nutrients). The additional recruitment period was considered to be an adaptive response over the normal pattern of twice yearly recruitment.
  • Two peaks (in July and September-October) were noted in the Limfjord (Jensen, 1988), with spat densities in excess of 20,000 m² recorded (see general biology).
  • Warwick & George (1980) inferred that settlement in Swansea Bay, Wales, occurred over a period of months between July and November.
Reproduction References Nott, 1980, Dauvin & Gentil, 1989, Dame, 1996, Jensen, 1988, Rees & Dare, 1993, Rainer, 1985, Warwick & George, 1980, Dewarumez, 1979,
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