BIOTIC

BIOTIC Species Information for Halidrys siliquosa
All Taxonomy Biology Distribution Reproduction

Researched by	Dr Harvey Tyler-Walters & Paolo Pizzolla	Data supplied by	MarLIN
Refereed by	Dr Stefan Kraan
General Biology
Growth form	Foliose	Feeding method	Photoautotroph
Mobility/Movement	Permanent attachment	Environmental position	Epilithic Epifloral
Typical food types	No text entered	Habit	Attached
Bioturbator	Not relevant	Flexibility	High (>45 degrees)
Fragility	Intermediate	Size	Large(>50cm)
Height	Occasionally up to 2 m	Growth Rate	Up to a maximum of 2 cm/month
Adult dispersal potential	None	Dependency	Independent
Sociability	Solitary
Toxic/Poisonous?	No
General Biology Additional Information	Although it is typically found in low abundances, Halidrys siliquosa can sometimes form beds (S. Kraan, pers. comm.). Growth rates The growth rate of newly germinated Halidrys siliquosa (germlings) was found to be dependant on temperature, light intensity and day length. For example: germlings grew up to ca 180 µm at 3 °C, up to ca 520 µm at 10 °C and up to ca 860 µm at 20 °C within 30 days of germination (Moss & Sheader, 1973); increased light intensity or day length had little effect on slow growth at 4 °C but doubling day length doubled growth rates at 10 °C although doubling total light did not double growth, and germlings grew faster but showed abnormal development at 20 °C (Moss & Sheader, 1973). Moss & Lacey (1963) reported a maximum summer growth rate of 2 cm /month, although this figure was based on a single specimen. Development The main axis develops its characteristic 'zigzag' form within 9 months in culture. Young plants (up to 1 year old) composed of 'leafy' branches only, branching in one plane. Air vesicles develop at the beginning of the second year of vegetative growth. Fertile receptacles develop towards the end of the plants second year i.e. at the end of autumn / start of winter (Moss & Lacey, 1963). In shallow rock pools or surf affected populations the plants are frequently damaged resulting in a turf-like growth form due to a proliferation of branches from the damaged main axis (Moss & Lacey, 1963). Seasonal changes Moss & Lacey (1963) studied Northumberland populations of Halidrys siliquosa and reported: rapid growth and elongation of the axis between spring and the end of July; proliferation of new 'leafy' branches in spring, reaching a maximum in June -July; production of air bladders from Sept -November and again in Feb to peak in April that was highly variable, and development of receptacles starting in July, becoming fertile in November and releasing gametes from December to March, after which the receptacles disintegrate. In appears, therefore, that growth and development follows a seasonal cycle of allocation of energy towards growth in spring, followed by allocation to reproduction later in the year. However, Wernberg et al. (2001) did not detect any significant seasonal change in biomass in the Limfjord, Denmark, due to high monthly variation in biomass, although the specimens they examined were small. They did not detect any seasonal change in thallus height or percentage cover. Epiphytes 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,