Sea oak (Halidrys siliquosa)
Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help
Researched by | Dr Harvey Tyler-Walters & Paolo Pizzolla | Refereed by | Dr Stefan Kraan |
Authority | (Linnaeus) Lyngbye, 1819 | ||
Other common names | - | Synonyms | - |
Summary
Description
A large sturdy brown alga 0.3 -1 m in length (occasionally up to 2 m) rising from a strong, flattened cone shaped holdfast. The main stem is flattened and branches alternately to give a distinctly zigzag appearance. The stem bears a few, flattened ribbon-like 'leafy' fronds. The ends of some branches bear characteristic pod-shaped air bladders (about 0.5 cm wide by 1-4 cm long) that are divided by transverse septa into 10 or 12 compartments. The branches also bear reproductive bodies that appear similar to the bladders but lack the septa. Young plants are olive-green in colour while older specimens are dark brown and leathery. This species is perennial.
Recorded distribution in Britain and 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).Habitat
A distinctive and common rock pool seaweed from the middle to lower shore (may be found in upper eulittoral but only in rock pools). It may also form a zone in the sublittoral below the lower limit of Laminaria digitata. It often supports a range of invertebrate epifauna such as bryozoans, hydroids and ascidians and epiflora such as small red algae, Ulva sp. and other fucoids.Depth range
Intertidal to 4 mIdentifying features
- Flattened cone shaped holdfast.
- Regularly alternately branched.
- Main stem 'zigzag' in appearance.
- Presence of terminal pod-shaped air bladders, resembling seed pods, divided by septa into 10 or 12 compartments.
Additional information
No text entered
Listed by
- none -
Biology review
Taxonomy
Level | Scientific name | Common name |
---|---|---|
Phylum | Ochrophyta | Brown and yellow-green seaweeds |
Class | Phaeophyceae | |
Order | Fucales | |
Family | Sargassaceae | |
Genus | Halidrys | |
Authority | (Linnaeus) Lyngbye, 1819 | |
Recent Synonyms |
Biology
Parameter | Data | ||
---|---|---|---|
Typical abundance | See additional information | ||
Male size range | |||
Male size at maturity | |||
Female size range | Large (>50 cm) | ||
Female size at maturity | |||
Growth form | Foliose | ||
Growth rate | Up to a maximum of 2 cm/month | ||
Body flexibility | High (greater than 45 degrees) | ||
Mobility | Sessile, permanent attachment | ||
Characteristic feeding method | Autotroph | ||
Diet/food source | Autotroph | ||
Typically feeds on | |||
Sociability | Solitary | ||
Environmental position | Epilithic | ||
Dependency | Independent. | ||
Supports | Substratum a number of epiphytic algae, hydroids, bryozoans and compound ascidians (Lewis, 1964; see additional information). | ||
Is the species harmful? | No information |
Biology 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 dependent 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 nine months in culture. Young plants (up to 1 year old) are 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 plant's second year i.e. at the end of autumn or the 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;
- the proliferation of new 'leafy' branches in spring, reaching a maximum in June to July;
- production of air bladders from Sept. to 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.
It appears, therefore, that growth and development follow 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 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. Laomedea 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).
Habitat preferences
Parameter | Data |
---|---|
Physiographic preferences | Open coast, Strait or Sound, Sea loch or Sea lough, Ria or Voe, Enclosed coast or Embayment |
Biological zone preferences | Lower eulittoral, Mid eulittoral, Sublittoral fringe, Upper infralittoral |
Substratum / habitat preferences | Bedrock, Cobbles, Large to very large boulders, Rockpools, Small boulders |
Tidal strength preferences | Moderately strong 1 to 3 knots (0.5-1.5 m/sec.), Very weak (negligible), Weak < 1 knot (<0.5 m/sec.) |
Wave exposure preferences | Exposed, Moderately exposed, Sheltered, Very sheltered |
Salinity preferences | Full (30-40 psu), Variable (18-40 psu) |
Depth range | Intertidal to 4 m |
Other preferences | No text entered |
Migration Pattern | Non-migratory or resident |
Habitat 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.Life history
Adult characteristics
Parameter | Data |
---|---|
Reproductive type | Permanent (synchronous) hermaphrodite |
Reproductive frequency | Annual episodic |
Fecundity (number of eggs) | >1,000,000 |
Generation time | 1-2 years |
Age at maturity | 2 years |
Season | December - March |
Life span | Insufficient information |
Larval characteristics
Parameter | Data |
---|---|
Larval/propagule type | - |
Larval/juvenile development | Spores (sexual / asexual) |
Duration of larval stage | < 1 day |
Larval dispersal potential | See additional information |
Larval settlement period | Insufficient information |
Life history information
Life history. 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 -100 µm in size) and male antheridia are shed simultaneously, so that fertilization may occur during or before liberation. Well developed zygotes were observed 12 hours 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 five or more days, after which two to four 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 plant's 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, germlings died after 140 days of darkness (Moss & Sheader, 1973). The ability to survive darkness and low light conditions, probably allows the germlings to survive under understorey algae, ready to develop should the shading canopy be removed.
Dispersal. 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 dependent 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.
Recruitment. Sousa et al. (1981) reported that the 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 dependent 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 three years after the 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 the removal of the kelp canopy, as well as by recruitment.
Sensitivity review
The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.
Physical pressures
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Intolerance | Recoverability | Sensitivity | Evidence / Confidence | |
Substratum loss [Show more]Substratum lossBenchmark. All of the substratum occupied by the species or biotope under consideration is removed. A single event is assumed for sensitivity assessment. Once the activity or event has stopped (or between regular events) suitable substratum remains or is deposited. Species or community recovery assumes that the substratum within the habitat preferences of the original species or community is present. Further details EvidenceRemoval of the substratum will result in removal of adults and germlings of Halidrys siliquosa. Therefore, an intolerance of high has been recorded. Recoverability has been assessed as high (see additional information below). | High | High | Moderate | Low |
Smothering [Show more]SmotheringBenchmark. All of the population of a species or an area of a biotope is smothered by sediment to a depth of 5 cm above the substratum for one month. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. Further details. EvidenceAdult plants are large and held upright by their air bladders when immersed. Therefore, smothering by 5 cm of sediment is likely to only cover the base of the plant and have little effect. Intertidal rock pool populations may be more intolerant, depending on the depth of the pool. However, young (up to 1 year old) plants do not bear air bladders, and, together with germlings, are likely to be smothered by the sediment, preventing photosynthesis, and potentially kill young plants. Germlings can survive for up to 120 days in the dark (Moss & Sheader, 1973), so may not be affected by smothering for a month (see benchmark), although any resultant anoxic conditions would probably be detrimental. The presence of a layer sediment has been shown to cause stress and considerable mortality in algal propagules, and sediment scour in flowing water may also remove and kill zygotes or germlings (Vadas et al., 1992). Smothering by epiphytes (see general biology) may reduce photosynthesis and increase drag on the thallus increasing its susceptibility to storm damage. Epiphyte communities have been shown to reduce light reaching the plant and decrease the rates of oxygen exchange with the surrounding water. This is especially true in eutrophic conditions, the result being a reduction in photosynthesis and metabolic stress in macrophytes (Sand-Jensen et al., 1985, Phillipart, 1995b) which will presumably affect macroalgae similarly. Nevertheless, Halidrys siliquosa is able to shed its outer cell walls in order to reduce surface epiphytes (Moss, 1982). Overall, younger or smaller plants, together with germlings may be killed and recruitment reduced. Therefore, an intolerance of intermediate and a high recoverability has been recorded (see additional information). | Intermediate | High | Low | Low |
Increase in suspended sediment [Show more]Increase in suspended sedimentBenchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details EvidenceIncreased suspended sediment concentrations will increase turbidity (see below). Suspended sediment settling on algal fronds is likely to reduce photosynthesis, and additional scour by sediment in water flow may adversely affect germling and reduce settlement. Halidrys siliquosa occurs in sheltered and very sheltered conditions, in which siltation rates may be high. Therefore, Halidrys siliquosa may tolerate suspended sediment and is unlikely to be significantly affected by an increase in suspended sediment concentrations for one month (see benchmark). Hence an intolerance of low has been recorded. Increased suspended sediment may reduce recruitment if it coincided with reproductive season. Recovery is likely to be rapid (see additional information below). | Low | Very high | Very Low | Low |
Decrease in suspended sediment [Show more]Decrease in suspended sedimentBenchmark. An arbitrary short-term, acute change in background suspended sediment concentration e.g., a change of 100 mg/l for one month. The resultant light attenuation effects are addressed under turbidity, and the effects of rapid settling out of suspended sediment are addressed under smothering. Further details EvidenceA decrease in suspended sediment is unlikely to have any direct affects on Halidrys siliquosa, except to decrease turbidity (see below). | Tolerant | Not relevant | Not sensitive | Not relevant |
Desiccation [Show more]Desiccation
EvidenceHalidrys siliquosa occurs subtidally, in the sublittoral fringe and is restricted to rockpools in the intertidal. Therefore, it is intolerant of desiccation. It is protected from exposure to desiccation in rockpools and subtidally, however, sublittoral fringe populations may be exposed to the air. Therefore, an increase in desiccation at the benchmark level is likely to adversely effect a proportion of the population and an intolerance of intermediate has been recorded. Recoverability has been assessed as high (see additional information below). | Intermediate | High | Low | Low |
Increase in emergence regime [Show more]Increase in emergence regimeBenchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details EvidenceA one hour increase in emergence is likely to expose the upper portion of the population, especially in the sublittoral fringe, to desiccation, increased wave action and an increased range of temperature change. Halidrys siliquosa is restricted to rock pools in the intertidal, therefore increased emergence is likely to result in loss of the exposed plants, a loss of a proportion of the population. Hence, intolerance has been assessed as intermediate with recoverability of high (see additional information below). | Intermediate | High | Low | Low |
Decrease in emergence regime [Show more]Decrease in emergence regimeBenchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details EvidenceDecreased emergence and hence, increased immersion may allow Halidrys siliquosa to colonize further up the shore. Therefore, the population may benefit overall. | Tolerant* | Not relevant | Not sensitive* | Low |
Increase in water flow rate [Show more]Increase in water flow rateA change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details EvidenceWater flow is important to supply nutrients and oxygen, and water flow has been shown to increase photosynthesis in Halidrys siliquosa (Schwenke, 1971). Halidrys siliquosa was reported from the 'rapids approaches' in association with Himanthallia elongata and Saccharina latissima (studied as Laminaria saccharina), and may occur in association with Laminaria digitata in strongly flowing tidal streams (Lewis, 1964). Halidrys siliquosa decreases in abundance with increasing water flow, so that in tidal rapids with current speeds of 2-3m/sec (ca 6 knots), it is replaced by Laminaria digitata, Laminaria hyperborea and Saccorhiza polyschides communities (Lewis, 1964; Schwenke, 1971). An increase in water flow from, for example, weak to strong (see benchmark) it likely to significantly reduce the population within a year, resulting in its replacement by species tolerant of strong water flow. Therefore, an intolerance of high has been recorded with a recoverability of high (see additional information below). | High | High | Moderate | Low |
Decrease in water flow rate [Show more]Decrease in water flow rateA change of two categories in water flow rate (view glossary) for 1 year, for example, from moderately strong (1-3 knots) to very weak (negligible). Further details EvidenceHalidrys siliquosa occurs in moderately strong to weak tidal streams, as well as in rock pools, and is probably tolerant on stagnant water in the short term. Therefore a further decrease in water flow is unlikely to have an adverse effect. Reduced water flow may reduce oxygen and nutrient exchange, therefore an intolerance of low has been recorded. Recoverability will probably be immediate. | Low | Immediate | Not sensitive | |
Increase in temperature [Show more]Increase in temperature
For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details EvidenceLüning (1984, 1990) reported an upper survival temperature of 25 °C after one week exposure in Halidrys siliquosa. It did not survive at the higher temperatures studied. Zygote germination and growth are temperature dependant. Moss & Sheader (1973) reported 50-97% germination at 3 and 10 °C, falling considerably to 8 -52% at 20 °C and to zero at 22 °C. Growth increased with temperature up to 20 °C but germlings developed abnormally at 20 °C (Moss & Sheader, 1973). | Tolerant | Not relevant | Not sensitive | Moderate |
Decrease in temperature [Show more]Decrease in temperature
For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details EvidenceLittle information concerning the effects of low temperatures on Halidrys siliquosa was found. Lüning (1984, 1990) reported that it survived at 0 °C for one week, and Moss & Sheader (1973) reported that the lower limit of germination was not reached at 3 °C but that no gametes were released from fertile receptacles at -4 °C. Halidrys siliquosa is protected from ice scour or severe frosts by its subtidal or rock pool habit. Overall, Halidrys siliquosa is recorded from northern Norway and is probably tolerant to decreases of temperature likely to occur in British waters. | Tolerant | Not relevant | Not sensitive | Low |
Increase in turbidity [Show more]Increase in turbidity
EvidenceIncreased turbidity decreases light penetration and hence decreases photosynthesis, plant growth and reproduction. Moss & Sheader (1973) demonstrated that the growth of germlings was dependent on light intensity but that germlings could survive total darkness for 120 days (see general biology). Halidrys siliquosa occurs in sheltered waters that may already be of medium to high turbidity (see benchmark), therefore an additional increase in turbidity may adversely effect the population. A short term increase may not have significant effects. An increase from medium to high turbidity for a year is likely to result in loss of the deepest extent of the population. Therefore, an intolerance of intermediate has been reported. Extreme turbidity for a year is likely to result in loss of macroalgae. Recoverability has been assessed as high (see additional information below). | Intermediate | High | Low | Low |
Decrease in turbidity [Show more]Decrease in turbidity
EvidenceDecreased turbidity and hence increased light penetration is likely to benefit all macroalgae present, and may allow the Halidrys siliquosa population to extend to greater depths. Moss & Sheader (1973) noted that Halidrys siliquosa germlings approached photosynthetic saturation at light intensities about 5 fold those of early sporophytes of Laminaria hyperborea, possibly an adaptation to exposure to high light intensities in rock pools. Therefore, the population is likely to benefit from decreased turbidity | Tolerant* | Not relevant | Not sensitive* | Low |
Increase in wave exposure [Show more]Increase in wave exposureA change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details EvidenceHalidrys siliquosa is most abundant on sheltered shores but is found on wave exposed shores where it occurs, primarily in deep mid-shore pools (Lewis, 1964). Halidrys siliquosa develops as a short, stunted turf in wave exposed pools (Moss & Lacey, 1963; Lewis, 1964) suggesting that it can tolerate strong water movement (Lewis, 1964). However, with increasing wave exposure Halidrys siliquosa / Saccharina latissima (studied as Laminaria saccharina) communities are replaced by Laminaria digitata or Laminaria hyperborea communities (Lewis, 1964). Therefore, intolerance of high has been recorded with a recoverability of high (see additional information). | High | High | Moderate | Moderate |
Decrease in wave exposure [Show more]Decrease in wave exposureA change of two ranks on the wave exposure scale (view glossary) e.g., from Exposed to Extremely exposed for a period of one year. Further details EvidenceHalidrys siliquosa is associated with wave sheltered rocky substrata (Lewis, 1964). A decrease in wave exposure is likely to allow Halidrys siliquosa to colonize space and to increase in extent. Therefore, the population may benefit from a decrease in wave exposure. | Tolerant* | Not relevant | Not sensitive* | Low |
Noise [Show more]Noise
EvidenceMacroalgae are not known to perceive noise of vibration. | Tolerant | Not relevant | Not sensitive | High |
Visual presence [Show more]Visual presenceBenchmark. The continuous presence for one month of moving objects not naturally found in the marine environment (e.g., boats, machinery, and humans) within the visual envelope of the species or community under consideration. Further details EvidenceAlthough macroalgae respond to light, they have no visual perception. | Tolerant | Not relevant | Not sensitive | High |
Abrasion & physical disturbance [Show more]Abrasion & physical disturbanceBenchmark. Force equivalent to a standard scallop dredge landing on or being dragged across the organism. A single event is assumed for assessment. This factor includes mechanical interference, crushing, physical blows against, or rubbing and erosion of the organism or habitat of interest. Where trampling is relevant, the evidence and trampling intensity will be reported in the rationale. Further details. EvidencePhysical disturbance by a scallop dredge (see benchmark) may damage or remove some individuals. Therefore, an intolerance of intermediate has been recorded. Damaged individuals with intact holdfasts, i.e. not removed, will probably survive. | Intermediate | High | Low | Low |
Displacement [Show more]DisplacementBenchmark. Removal of the organism from the substratum and displacement from its original position onto a suitable substratum. A single event is assumed for assessment. Further details EvidenceHalidrys siliquosa is permanently attached to the substratum and once removed would not be able to reattach. Therefore, displaced individuals would be lost and an intolerance of high has been recorded. Recoverability has been assessed as high (see additional information below). | High | High | Moderate | Low |
Chemical pressures
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Intolerance | Recoverability | Sensitivity | Evidence / Confidence | |
Synthetic compound contamination [Show more]Synthetic compound contaminationSensitivity is assessed against the available evidence for the effects of contaminants on the species (or closely related species at low confidence) or community of interest. For example:
The evidence used is stated in the rationale. Where the assessment can be based on a known activity then this is stated. The tolerance to contaminants of species of interest will be included in the rationale when available; together with relevant supporting material. Further details. EvidenceNo information on the intolerance of Halidrys siliquosa to synthetic chemicals was found, however, information on other Fucales was available. | Intermediate | High | Low | Very low |
Heavy metal contamination [Show more]Heavy metal contaminationEvidenceHolt et al., (1995, 1997) reported that fucoids and other algae were capable of retaining and concentrating heavy metals, so much so that Fucus spp. are used as indicators of heavy metal pollution. Alginates found in fucoids (and in Halidrys siliquosa) strip heavy metals and some radionuclides from seawater and store them in inert forms. Hence, adult plants are considered to be relatively tolerant of heavy metal contamination. however, younger stages may be more intolerant. for example iron ore dust interfered with the interaction between eggs and sperm in Fucus serratus (Boney, 1980; cited in Bryan, 1984). Bryan (1984) also reported that heavy metals retarded growth in brown algae, and suggested that heavy metal toxicities to seaweeds was in the order of Hg>Cu>Ag>Zn>Zn>Cd>Pb. | Low | Very high | Very Low | Moderate |
Hydrocarbon contamination [Show more]Hydrocarbon contaminationEvidenceHalidrys siliquosa is protected from the direct effects of oil spills due to its subtidal habit, although sublittoral fringe and rock pool populations will be more vulnerable. However, plants may be exposed to water soluble components of the oil or oil adsorbed on to particulates. | Low | Very high | Very Low | Low |
Radionuclide contamination [Show more]Radionuclide contaminationEvidenceRyan et al (2003) report on radioactivity levels in various fucoids around Ireland although no specific information was found on either Halidrys siliquosa or effects on fucoids in general. | No information | Not relevant | No information | Not relevant |
Changes in nutrient levels [Show more]Changes in nutrient levelsEvidenceWernberg et al. (2001) reported that the N:P (nitrogen to phosphorus) ratio in Limfjorden Halidrys siliquosa was low in summer and high in spring, which suggested that growth was nutrient limited by P in spring and N in summer. Kindig & Littler (1980) exposed Halidrys dioica and other algae to 10% untreated sewage effluent in the field, which resulted in increased gross productivity. However, Halidrys dioica was found to be absent in the vicinity of a sewage outfall, and Kindig & Littler (1980) concluded that another component of the effluent, other than nutrient, was responsible. Overall, therefore, it would appear that moderate nutrient enrichment at the benchmark level may stimulate growth of Halidrys spp. However, excessive enrichment may lead to eutrophication, decreased oxygen levels (see below) and the potential smothering of Halidrys sp. by microfloral epiphytes (see smothering). | Tolerant* | Not relevant | Not sensitive* | Moderate |
Increase in salinity [Show more]Increase in salinity
EvidenceNo information on salinity tolerance was found. However, Halidrys siliquosa occurs in rock pools, which may experience considerable fluctuations in salinity due to evaporation on hot days. Therefore, Halidrys siliquosa is probably tolerant of fluctuations in salinity, both increases and decreases, and an intolerance of low has been recorded. | Low | Very high | Very Low | Very low |
Decrease in salinity [Show more]Decrease in salinity
EvidenceNo information on salinity tolerance was found. However, Halidrys siliquosa occurs in rock pools, which may experience considerable decline in salinity due to freshwater influence during rain. Therefore, Halidrys siliquosa is probably tolerant of fluctuations in salinity, both increases and decreases, and an intolerance of low has been recorded. | Low | Very high | Very Low | |
Changes in oxygenation [Show more]Changes in oxygenationBenchmark. Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details. EvidenceLittle information on the effects of oxygen depletion on macroalgae was found. Kinne (1972) reports that reduced oxygen concentrations inhibit both photosynthesis and respiration. The effects of decreased oxygen concentration equivalent to the benchmark would be greatest during dark when the macroalgae are dependant on respiration. | No information | Not relevant | No information | Not relevant |
Biological pressures
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Intolerance | Recoverability | Sensitivity | Evidence / Confidence | |
Introduction of microbial pathogens/parasites [Show more]Introduction of microbial pathogens/parasitesBenchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details. EvidenceHalidrys siliquosa supports a number of epiphytic species, which use it as a substratum but are not parasitic on the plant. No information on diseases was found. | No information | Not relevant | No information | Not relevant |
Introduction of non-native species [Show more]Introduction of non-native speciesSensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details. EvidenceHalidrys siliquosa has been reported to be displaced as the dominant species in rock pools by the non-native Sargassum muticum on the south coast of England (Eno et al., 1997). Staehr et al. (2000) reported that an increase in the abundance of Sargassum muticum in Limfjorden, Denmark had resulted in a significant decline of the cover of large brown algae, especially Saccharina latissima (studied as Laminaria saccharina), Halidrys siliquosa, Codium fragile and Fucus vesiculosus. | High | High | Moderate | High |
Extraction of this species [Show more]Extraction of this speciesBenchmark. Extraction removes 50% of the species or community from the area under consideration. Sensitivity will be assessed as 'intermediate'. The habitat remains intact or recovers rapidly. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details. EvidenceNo evidence of the extraction or harvesting of Halidrys siliquosa was found. | Not relevant | Not relevant | Not relevant | Not relevant |
Extraction of other species [Show more]Extraction of other speciesBenchmark. A species that is a required host or prey for the species under consideration (and assuming that no alternative host exists) or a keystone species in a biotope is removed. Any effects of the extraction process on the habitat itself are addressed under other factors, e.g. displacement, abrasion and physical disturbance, and substratum loss. Further details. EvidenceSvendsen (1972; summary only) reported that Halidrys siliquosa became one of the dominant macroalgae, 3 years after kelp harvesting in Norway. This suggests that removal of other algae species that compete with Halidrys siliquosa for space and light would be beneficial. | Tolerant* | Not relevant | Not sensitive* | Low |
Additional information
Recoverability. Little information concerning recruitment in Halidrys siliquosa was found. The congeneric %Halidrys dioica% was shown to recruit to cleared areas within three to four months in the absence of sea urchins on the California coast (Sousa et al., 1981). Similarly, Halidrys siliquosa became a dominant alga three years after the removal of kelps in Norway (summary only, Svendsen, 1972). Several fucoids have been shown to recolonize cleared areas readily, especially in the absence of grazers (Holt et al., 1995, 1997). For example, Fucus dominated areas may take 1-3 years to recolonize in British waters (Holt et al., 1995).
Overall, Halidrys siliquosa is highly fecund and widespread in British waters. If a population is damaged or reduced in abundance it is likely that local recruitment will be good, especially in the winter months and prior abundance may return within a few years. Should the population be destroyed, then recruitment from the surrounding area and subsequent growth may take longer, possibly up to five years.
Importance review
Policy/legislation
- no data -
Status
National (GB) importance | - | Global red list (IUCN) category | - |
Non-native
Parameter | Data |
---|---|
Native | - |
Origin | - |
Date Arrived | Not relevant |
Importance information
Halidrys siliquosa provides substratum for a number of epiphytic species (see general biology).Bibliography
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Datasets
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Citation
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Last Updated: 29/05/2008