BIOTIC

BIOTIC Species Information for Cerastoderma edule

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

Spawn over summer

Reproductive Location

Water column

Reproductive frequency

Annual protracted

Regeneration potential

Life span

6-10 years

Age at reproductive maturity

1-2 years

Generation time

1-2 years

Fecundity

Egg/propagule size

75 µm diameter

Fertilization type

External

Larvae/Juveniles
Larval/Juvenile dispersal potential	Insufficient information	Larval settlement period	May to September but varies (see additional info)
Duration of larval stage

Reproduction Preferences Additional Information

Longevity and sexual maturity
Cerastoderma edule may live for up to 9 years or more in some habitats but 2 -4 years is normal. The sex ratio was reported to be 40% males to 60% females (Fretter & Graham, 1964). Adults first mature and spawn in their second summer, at about 18 months old and 15-20 mm in length, however, large cockles (>15 mm) may mature in their first year suggesting that size and maturity are linked (Orton, 1926; Hancock & Franklin, 1972; Seed & Brown, 1977).
Reproductive cycle
Gametogenesis is initiated in winter (October to March) but increases rapidly in spring (February -April) (Newell & Bayne, 1980) and the majority of the population are ripe by mid-summer (Seed & Brown, 1977). Most adults spawn in a short peak period over summer with remaining adults spawning over a protracted period, resulting in a short (ca. 3 month) period of peak settlement followed by generally declining numbers of recruits (Hancock, 1967; Seed & Brown, 1977). Spawning generally occurs between March - August in the UK followed by peak spatfall between May and September, however the exact dates vary between sites in the UK and Europe (Seed & Brown, 1977; Newell & Bayne, 1980). Boyden (1971) suggested that warming of water in spring to 13 °C or above was required to induce spawning, however Ducrotoy et al. (1991) suggested that a sudden temperature rise (rather than an absolute level) was probably required to initiate spawning. An occasional late peak in settlement may occur e.g. on the Llanrhidian Sands, Hancock (1967) reported an additional settlement peak in August -September after the main peak in May -July.
Development
Fertilization is external. Males may release about 15 million sperm/sec and females were reported to release about 1900 eggs/sec. Gamete viability is short and André & Lindegarth (1995) found that fertilization was reduced to 50% in 2 hours and that no fertilization was observed after 4 -8 hrs. André & Lindegarth (1995) noted that fertilization efficiency was dependant on sperm concentration so that at high water flow rates fertilisation was only likely between close individuals. However, this may be compensated for by high population densities and synchronous spawning of a large proportion of the population. Eggs (50-60µm) develop into a trochophore stage within the egg membrane and then into a typical bivalve veliger at ca. 80µm, the D -larvae (so called due to the D -shaped shell) after about 3 -4 days the foot develops and the veliger metamorphoses into a juvenile cockle (pediveliger) at ca. 270µm after about 3 -5 weeks (Lebour, 1938; Creek, 1960). The juveniles reach ca. 600-700µm after about 3 weeks, and by 3 months are ca. 0.75-1.5 mm long (Creek, 1960).
Recruitment
Settlement and subsequent recruitment has a significant impact on the dynamics of Cerastoderma edule populations, in many but not all circumstances (Olaffsson et al., 1994). Settlement and recruitment is sporadic and varies with geographic location, year, season, reproductive condition of the adults and climatic variation. Factors reported to affect recruitment follow.

Geographical location (Ducrotoy et al. 1991; Olaffsson et al., 1994).
Annual variation in climate. Ducrotoy et al. (1991) reported the variation in annual recruitment between years for several sites in Europe, and noted a correlation between good recruitment and a previous severe winter (presumably due to high adult mortality, reduced population density of adults and reduced numbers of infaunal predators), in many but not all cases.
Good recruitment was also observed after heavy storm surges reduced the adult population (Ducrotoy et al. 1991).
Post-settlement erosion and surface sediment erosion by currents and storms. Juveniles may be transported by currents until 2mm in size and high densities of juveniles may be swept away by winter storms resulting in subsequent patterns of adult distribution (Olaffsson et al., 1994).
Post-settlement mortalities of 60-96% have been reported, resulting from intra and interspecific mortality and predation (Sanchez-Salazar et al., 1987a; Montaudouin & Bachelet, 1996; André et al.,1993; Guillou & Tartu, 1994).
Adult suspension feeders, including adult cockles, may reduce settlement by ingestion of settling larvae and juveniles or smothering by sediment displaced in burrowing and feeding (Montaudouin & Bachelet, 1996). Therefore, recruitment may be dependant on adult population density (André et al.,1993). André et al. (1993) observed that adults inhaled 75% of larvae at 380 adults/m², which were also ingested. However, Montaudouin & Bachelet, (1996) noted that adults that inhaled juveniles, rejected them and closed their siphons but that rejected juveniles usually died.
Predation (see distribution) (Dame, 1996; Sanchez-Salazar et al. 1987a).
Guillou & Tartu (194) noted that spat also suffered from mortality in their first year in the spring following their settlement, even through food was available, probably due to exhausted energy reserves (after winter) and spring predation from shore crabs.

Ducrotoy et al. (1991; Figure 14) identified, 'crisis', 'recovery', 'upholding', and 'decline' phases in dynamics of Cerastoderma edule populations. Each phase is characterised by:

'Crisis': a few age classes and successive spawnings and maximal growth due to low density;
'Recovery': single high density recruitment to first year class (breeding stocks may be synchronised by severe temperatures);
'Upholding': several age classes, higher densities of older age classes, seasonal recruitment, and low growth rate;
'Decline': reducing abundance, adult mortality or unsuccessful recruitment due to climatic factors, lower food levels, competition or parasitic infection.

Ducrotoy et al. (1991) suggested that increased growth rate indicated instability. Any population may exhibit these characteristics at different times or location.

Reproduction References

Fretter & Graham, 1964, Seed & Brown, 1977, Hancock & Franklin, 1972, Jones & Baxter, 1987a, Richardson et al., 1980, Orton, 1926, Newell & Bayne, 1980, Montaudouin & Bachelet, 1996, Ducrotoy et al. , 1991, Jensen, 1993, Lebour, 1938, Creek, 1960, Sanchez-Salazar et al. 1987, Olafsson et al., 1994., André et al. , 1993, Guillou & Tartu, 1994, Möller & Rosenberg, 1983, Hummel & Bogaaards, 1989, Kingston, 1974, Rygg, 1970, Ansell et al., 1981, Eckert, 2003, Julie Bremner, unpub data,