BIOTIC Species Information for Halidrys siliquosa
Researched byDr Harvey Tyler-Walters & Paolo Pizzolla Data supplied byMarLIN
Refereed byDr Stefan Kraan
Reproduction/Life History
Reproductive typePermanent hermaphrodite
Developmental mechanismSpores (sexual / asexual)
Reproductive SeasonDecember to March Reproductive LocationInsufficient information
Reproductive frequencyAnnual episodic Regeneration potential No
Life spanInsufficient information Age at reproductive maturity1-2 years
Generation time1-2 years FecundityInsufficient information
Egg/propagule sizeInsufficient information Fertilization typeInsufficient information
Larval/Juvenile dispersal potential100-1000m Larval settlement periodInsufficient information
Duration of larval stage<1 day   
Reproduction Preferences Additional InformationFucales, such as Halidrys siliquosa, have a single vegetative sporophyte stage, the diploid thallus that bears specialized reproductive bodies (meiosporangia) in the receptacles, in which the gametes are formed. Female gametes are large and immotile (oogonia) while the male gametes are small and motile (antheridia) (van den Hoek et al., 1995).
In Halidrys siliquosa, gametes are formed shortly before liberation from the receptacles. Female oogonia (80 -100µm in size) and male antheridia are shed simultaneously, so that fertilization may occur during or before liberation. Well developed zygotes were observed 12hrs after fertilization. Zygotes probably sink rapidly (especially if they cluster together), are covered in adhesive mucus and stick to the substratum. Further development is delayed for 5 or more days, after which 2-4 rhizoids develop and fix the zygote to the substratum. The early zygote wall is shed and the germling develops further (Moss & Sheader, 1973; Hardy & Moss, 1978).

In Northumberland, receptacles began to develop in July, became fertile in November and released gametes from December to March, after which the receptacles disintegrated. Fertile receptacles developed in the plants second year (Moss & Lacey, 1963).

Germlings are capable of growing in the dark for up to 40 days. In addition, germlings maintained in the dark for up to 120 days were able to resume growth when exposed to light, however, after 140 days of darkness germlings died (Moss & Sheader, 1973). The ability to survive darkness, and low light conditions, probably allows the germlings to survive under understory algae, ready to develop should the shading canopy be removed.
Zygotes are large and may form clusters (Hardy & Moss, 1978) and probably sink rapidly. Norton (1992) suggested that turbulent deposition by water flow (zygotes or spores being thrown against the substratum) was the most important force directing propagules to the substratum. Dispersal by spores is probably dependant on the hydrographic regime but is probably localized, e.g. in Sargassum muticum. Although some zygotes may settle 1km of more from the parent, most settle within 2m (Norton, 1992). The propagules of most fucales tend to settle near the parent plant (Norton, 1992; Holt et al., 1997). Halidrys siliquosa can float if detached, suggesting another potential route for dispersal. Floating plants remain fertile and spores may be released some distance from the point of detachment. However, although some long range dispersal must occur in macroalgae (resulting in colonization of oil rigs and similar structures), van den Hoek (1987) and Norton (1992) suggested that it is probably ineffective for most species of macroalgae. Wernberg et al. (2001) suggested that the lack of long range dispersal success in Halidrys siliquosa was responsible for its regional distribution in the north east Atlantic.
Sousa et al. (1981) reported that experimental removal of sea urchins significantly increased recruitment in long-lived brown algae. In experimental plots cleared of algae and sea urchins in December, Halidrys dioica colonized the plots, in small numbers, within 3-4 months. Plots cleared in August received few , if any recruits, suggesting that recolonization was dependant on zygote availability and therefore the season. Halidrys dioica did not colonize plots grazed by urchins in their experiments (Sousa et al., 1981). Svendsen (summary only, 1972) reported that Halidrys siliquosa became one of a few dominant algae 3 years after removal of Laminaria hyperborea by harvesting on the west coast of Norway. However, this observation may be explained by the growth of small germlings already present due to increased light and space freed by removal of the kelp canopy, as well as by recruitment.
Reproduction References Wernberg et al., 2001, Lobban & Harrison, 1997, Hoek van den et al., 1995, Moss & Sheader, 1973, Moss & Lacey, 1963, Hardy & Moss, 1978, Hoek van den, 1987, Norton, 1992, Svendsen, 1972, Holt et al., 1997, Vadas et al., 1992, Sousa et al., 1981,
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