BIOTIC

BIOTIC Species Information for Abra alba

Researched by

Lizzie Tyler

Data supplied by

University of Sheffield

Refereed by

This information is not refereed.

Taxonomy

Scientific name

Abra alba

Common name

White furrow shell

MCS Code

W2059

Recent Synonyms

None

Phylum

Mollusca

Subphylum

Superclass

Class

Pelecypoda

Subclass

Order

Veneroida

Suborder

Family

Semelidae

Genus

Abra

Species

alba

Subspecies

Additional Information

Abra 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 form

Bivalved

Feeding method

Passive suspension feeder
Active suspension feeder
Surface deposit feeder
Sub-surface deposit feeder

Mobility/Movement

Burrower

Environmental position

Infaunal

Typical food types

Phytoplankton, detritus.

Habit

Burrow dwelling

Bioturbator

Flexibility

None (< 10 degrees)

Fragility

Intermediate

Size

Small(1-2cm)

Height

Insufficient information

Growth Rate

0.1 mm/day

Adult dispersal potential

100-1000m

Dependency

Independent

Sociability

Solitary

Toxic/Poisonous?

General Biology Additional Information

Abundance
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 & Ireland

Widespread around the British Isles.

Global distribution

Abra 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 range

Not researched

Depth range

0 - 60 m

Migratory

Non-migratory / Resident

Distribution Additional Information

Dispersal 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 preferences

Muddy gravel
Sandy mud
Mud
Muddy sand

Physiographic preferences

Open coast
Offshore seabed
Strait / sound
Sealoch
Enclosed coast / Embayment

Biological zone

Sublittoral Fringe
Upper Infralittoral
Lower Infralittoral
Upper Circalittoral
Lower Circalittoral

Wave exposure

Sheltered

Tidal stream strength/Water flow

Weak (<1 kn)

Salinity

Full (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 type

Gonochoristic

Developmental mechanism

Planktotrophic

Reproductive Season

February to Autumn

Reproductive Location

Water column

Reproductive frequency

Annual protracted

Regeneration potential

Life span

1-2 years

Age at reproductive maturity

Generation time

<1 year

Fecundity

17000

Egg/propagule size

60 µm diameter

Fertilization type

External

Larvae/Juveniles
Larval/Juvenile dispersal potential	>10km	Larval settlement period	Insufficient information
Duration of larval stage	1-2 months

Reproduction Preferences Additional Information

Gametogenesis
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,