BIOTIC Species Information for Alaria esculenta
Researched byDr Harvey Tyler-Walters Data supplied byMarLIN
Refereed byDr Stefan Kraan
Reproduction/Life History
Reproductive typeAlternation of generations
Developmental mechanismSpores (sexual / asexual)
Reproductive SeasonInsufficient information Reproductive LocationWater column
Reproductive frequencyAnnual episodic Regeneration potential No
Life span3-5 years Age at reproductive maturity<1 year
Generation time1 year Fecundity>1,000,000
Egg/propagule size Fertilization typeExternal
Larval/Juvenile dispersal potential10-100m Larval settlement period
Duration of larval stage1 day   
Reproduction Preferences Additional InformationThe fecundity reported above is for zoospore production. Both the sporophyte and gametophyte are photoautotrophs but only the gametophyte may develop vegetatively.
  • Dispersal potential varies with phase in the life cycle; zoospores may disperse <2m whereas gametophytes may disperse between 1 -10 m by drifting, maybe up to 100 m (Kraan pers. comm.).
  • Alaria esculenta is a perennial and lives for 4 -5 years in the Irish Sea and up to 7 years in Norway.
  • Two rows of ligulate sporophylls form in the upper parts of the stipe during spring and in a lesser amount in autumn only (Kraan pers. comm.; Widdowson, 1971).
  • New sporophytes appear in early spring and zoospores are produced from sporophylls between October and May (Kraan pers. comm.; Birkett et al., 1998b).
  • The sporophylls produce haploid spores (zoospores), by meiosis, that germinate to form the haploid or gametophytic phase (male and female). Gametophytes produce the gametes (sperm and eggs) which fuse after fertilization to form a zygote. The zygotes germinates to form diploid platelets (germlings), the sporophytic phase. Thus the life history is that the large seaweed (sporophyte) alternates with a microscopic filamentous phase (Hoek van den, 1995). Therefore, Alaria esculenta is dioecious and has a heteromorphic diplohaplontic life history.
  • The flagellated zoospores are about 5 microns in diameter. They loose their flagella after 24 hrs and settle on the available substrata (Birkett et al., 1998b). However, settling rate is dependant on the local currents, therefore spore settling time is probably longer than 1 day.
  • Sundene (1961) noted that next generation sporophytes developed within 10 m of the parent plants in Drobak, Norway. Norton (1992) suggested that the position of the sporophylls close to the substratum may limit dispersal potential, however the local currents are probably of overriding importance for dispersal.
  • Gametophytes become fertile in under 10 days in optimal conditions.
  • Successful fertilization requires a high density of spore settlement (about 1 mm apart).
  • Maturation of the gametophytes can be delayed under less optimal conditions, for example, low light, and development remains vegetative. Fragments of damaged vegetative gametophytes may develop into separate gametophytes (only a few cells are required) hence reproductive potential may be increased. If optimal conditions return the gametophyte may become fertile and produce gametes.
  • Spore production may be inhibited by epifauna such as Membranipora membranacea (sea mat) and endophytes such as Streblonema sp.
Reproduction References Birkett et al., 1998b, Lüning, 1990, Lobban & Harrison, 1997, Stein et al., 1995, Guiry & Blunden, 1991, Sundene, 1962, Dring, 1982, Lein et al., 1991, Norton, 1992, Kain & Dawes, 1987,
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