BIOTIC Species Information for Halidrys siliquosa
|Researched by||Dr Harvey Tyler-Walters & Paolo Pizzolla||Data supplied by||MarLIN|
|Refereed by||Dr Stefan Kraan|
|Scientific name||Halidrys siliquosa||Common name||Sea oak|
|MCS Code||ZR372||Recent Synonyms||None|
|Additional Information||No text entered|
|Taxonomy References||Fish & Fish, 1996, Dickinson, 1963, Hayward et al., 1996, Gibson et al., 2001, Hiscock, 1979, Hoek van den et al., 1995,|
|Typical food types||No text entered||Habit||Attached|
|Bioturbator||Not relevant||Flexibility||High (>45 degrees)|
|Height||Occasionally up to 2 m||Growth Rate||Up to a maximum of 2 cm/month|
|Adult dispersal potential||None||Dependency||Independent|
|General Biology Additional Information||Although it is typically found in low abundances, Halidrys siliquosa can sometimes form beds (S. Kraan, pers. comm.).
The growth rate of newly germinated Halidrys siliquosa (germlings) was found to be dependant on temperature, light intensity and day length. For example:
Moss & Lacey (1963) studied Northumberland populations of Halidrys siliquosa and reported:
Halidrys siliquosa has been reported to support a number of epiphytic species, depending on location, including microflora (e.g. bacteria, blue green algae, diatoms and juvenile larger algae), Ulothrix and Ceramium sp., hydroids (e.g. Laomeda flexuosa and Obelia spp.), bryozoans (e.g. Scrupocellaria spp.), and ascidians (e.g. Apilidium spp. and Botrylloides leachi ). However, Halidrys siliquosa was considered to be relatively clear of epiphytes due to its ability to shed the outer layer of epidermal cell walls, together with adherent epiphytes (Moss, 1982; Lobban & Harrison, 1997).
|Biology References||Hayward et al., 1996, Gibson et al., 2001, Hiscock, 1979, Lüning, 1990, Lewis, 1964, Moss, 1982, Wernberg et al., 2001, Lüning, 1990, Lobban & Harrison, 1997, Hoek van den et al., 1995, Moss & Sheader, 1973, Moss & Lacey, 1963,|
|Distribution and Habitat|
|Distribution in Britain & Ireland||Widely distributed and fairly common in the Britain and Ireland.|
|Global distribution||Restricted to the north east Atlantic, and recorded from northern Norway, Scandinavia, the Baltic Sea, Helgoland and the Netherlands south to the Bay of Biscay, north Portugal and the Canary Islands (John et al., 2004).|
|Biogeographic range||Not researched||Depth range||Intertidal to 4 m|
|Migratory||Non-migratory / Resident|
|Distribution Additional Information||On wave sheltered shores Halidrys siliquosa occur in the sublittoral and rock pools at low water. However, on wave exposed sites Halidrys siliquosa may also be found in deep high shore rock pools sheltered from the sun (Moss & Lacey, 1963). It is in such rock pools where the very weak water flow rate is likely to occur.|
Large to very large boulders
|Physiographic preferences||Open coast
Strait / sound
Ria / Voe
Enclosed coast / Embayment
|Biological zone||Mid Eulittoral
|Tidal stream strength/Water flow||Moderately Strong (1-3 kn)
Weak (<1 kn)
Very Weak (negligible)
|Salinity||Full (30-40 psu)
Variable (18-40 psu)
|Habitat Preferences Additional Information|
|Distribution References||Fish & Fish, 1996, Dickinson, 1963, Norton, 1985, Hayward et al., 1996, Gibson et al., 2001, Lüning, 1990, JNCC, 1999, Picton & Costello, 1998, Lewis, 1964, Lüning, 1990, Guiry & Nic Dhonncha, 2002, Hardy & Guiry, 2003, Guiry & Nic Dhonncha, 2002, John et al., 2004,|
|Reproductive type||Permanent hermaphrodite
||Developmental mechanism||Spores (sexual / asexual)
|Reproductive Season||December to March||Reproductive Location||Insufficient information|
|Reproductive frequency||Annual episodic||Regeneration potential||No|
|Life span||Insufficient information||Age at reproductive maturity||1-2 years|
|Generation time||1-2 years||Fecundity||Insufficient information|
|Egg/propagule size||Insufficient information||Fertilization type||Insufficient information|
|Reproduction Preferences Additional Information||Fucales, 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,|