BIOTIC

BIOTIC Species Information for Abra alba

Researched by

Lizzie Tyler

Data supplied by

University of Sheffield

Refereed by

This information is not refereed.

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,