BIOTIC Species Information for Modiolus modiolus
Click here to view the MarLIN Key Information Review for Modiolus modiolus
Researched byLizzie Tyler Data supplied byUniversity of Sheffield
Refereed byThis information is not refereed.
Reproduction/Life History
Reproductive typeGonochoristic
Developmental mechanismPlanktotrophic
Reproductive SeasonSee additional information Reproductive LocationInsufficient information
Reproductive frequency Regeneration potential No
Life span51-100 years Age at reproductive maturity6-10 years
Generation time6-10 years Fecundity1000000
Egg/propagule size Fertilization typeInsufficient information
Larval/Juvenile dispersal potential>10km Larval settlement periodInsufficient information
Duration of larval stage11-30 days   
Reproduction Preferences Additional InformationLife span
Mussels over 25 years old are frequent in British populations, with occasional records of individuals of up to 35 years old. However, maximum ages are thought likely to be in excess of 50 years (Anwar et al., 1990).

The spawning season is variable or unclear and varies with depth and geographic location, probably related to temperature (de Schwienitz & Lutz, 1976; reviewed by Brown, 1984; Holt et al., 1998). For example:
  • in Strangford Lough, Ireland the population exhibits a slow, continuous release of gametes (Seed & Brown, 1977; Brown & Seed, 1977);
  • populations off south east of the Isle of Man show an annual gametogenesis and spawning cycle, with continuous release of gametes and a peak in spring and summer (Jasim & Brand; 1989);
  • Scottish populations showed a slow release of gametes throughout the year with peaks of spawning in spring and summer in some areas (Comely, 1978);
  • Swedish and northern Norwegian populations showed a distinct spawning in June -July respectively (Brown, 1984), and
  • Wiborg (1946) reported that spawning occurring only every 2nd to 3rd year in Norwegian waters.
Brown (1984) suggested that Modiolus modiolus commenced spawning over a narrow range of temperatures (7 -10°C), timed with suitable conditions for larval development. Brown (1984) also suggested that the suitable spawning temperature may limit this species' northern distribution.

Recruitment is sporadic and highly variable seasonally, annually or with location (geographic and depth) (Holt et al., 1998). For example:
  • settlement in Bristol Channel populations is dense but subsequent recruitment is low (Holt et al., 1998);
  • regular recruitment occurs in populations in Strangford Lough and in two areas south east of the Isle of Man (Seed & Brown, 1978; Jasim & Brand, 1986).
  • very irregular recruitment, with gaps of many years was reported for Norwegian (Wiborg, 1946) and Canadian populations (Rowell, 1967).
  • Scottish populations varied, with 'normal' recruitment occurring in areas of strong currents, resulting in a relatively young population, while recruitment was negligible in areas of quiet water resulting in an ageing population, and in a deep water population no recruitment had occurred for a number of years and the population was old, possibly senile and dying out (Comely, 1978).
Comely (1978) suggested that recruitment was dependant on larvae from outside the area in areas of free water movement. In open coast areas, e.g. the Llyn Peninsula and Sarnau, released larvae are probably swept away from the adult population (Comely, 1978; Holt et al., 1998). Holt et al., (1998) cite unpublished preliminary genetic data that suggest that beds off the south east of the Isle of Man receive recruits from other areas, albeit in a sporadic manner. Holt et al., (1998) suggested that enclosed areas such as Strangford Lough and the Scottish sea lochs would be relatively self sustaining. Therefore, recruitment is probably strongly affected by the local hydrographic regime.

Post-settlement mortality
Widdows (1991) noted that in Mytilus edulis larvae any environmental factor that increased the larval development time (e.g. temperature or food availability) increased larval mortality. This is probably true for other mytilid larvae, such as Modiolus modiolus.
Pre- and post-settlement mortality is high due to predation. Settling larvae prefer the byssus threads and aggregations or clumps of adults which provide a refuge from predators. In infaunal populations, however, the byssal threads and clumps of adults will be less accessible, and predation risk higher as a result (Holt et al., 1998). Most populations exhibit a bimodal size distribution of large, older specimens and small, younger specimens. Newly-settled horse mussels exhibit rapid growth prior to reaching maturity (see general biology), investing energy in growth rather than reproduction. Selection favours rapid growth to a size that is relatively immune to predation. Only the largest starfish and crabs can open mussels greater than 45-60mm and large horse mussels are thought to be largely predator free (Roberts, 1975; Seed & Brown, 1978; Holt et al., 1998). Comely (1978) noted that Modiolus modiolus <40mm were rarely found away from large horse mussels.
Reproduction References Holt et al., 1998, Brown & Seed, 1977, Comely, 1978, Schweinitz de & Lutz, 1976, Brown, 1984, Seed & Brown, 1978, Anwar et al., 1990, Seed, 1976, Jones et al., 2000, Seed & Brown, 1977, Jasim & Brand, 1989, Wiborg, 1946, Roberts, 1975, Seed & Brown, 1975, Jasim, 1986, Rowell, 1967, Julie Bremner, unpub data, Brown & Seed, 1977,
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