Two-headed wrack (Fucus distichus)
Fucus distichus on rocky shore.
Photographer: Keith Hiscock Copyright: Dr Keith Hiscock
Fucus distichus
Photographer: Robert Beharie Copyright: Robert Beharie
Fucus distichus
Photographer: Robert Beharie Copyright: Robert Beharie
Distribution data supplied by the Ocean Biodiversity Information System (OBIS). To interrogate UK data visit the NBN Atlas.Map Help
| Researched by | Nicola White | Refereed by | Dr Graham Scott |
| Authority | Linnaeus, 1767 | ||
| Other common names | - | Synonyms | Fucus distichus distichus Powell 1957a, Fucus distichus anceps Linnaeus, 1767 |
Summary
Description
A small tufted brown alga. It has narrow fronds without airbladders and short receptacles. The species has a lifespan of 3 years and grows up to 30 cm long.
Recorded distribution in Britain and Ireland
Restricted to northern shores of Scotland and north and west Ireland.
Global distribution
Norway, northern Scotland, Iceland, Greenland, eastern North America from Labrador to Maine and the Pacific coast of America discontinuously from Alaska to California
Habitat
Occurs in rock pools and on rock faces in the upper eulittoral at wave exposed locations in Scotland & Ireland.
Depth range
Not relevantIdentifying features
- Narrow frond without airbladders.
- Caecostomata rare.
- Receptacles short, typically 18 mm, max. 40 mm.
- Plants small, typically 10 cm long at maturity (max. 30 cm).
Additional information
No text entered
Listed by
Biology review
Taxonomy
| Phylum | Ochrophyta | Brown and yellow-green seaweeds |
| Class | Phaeophyceae | |
| Order | Fucales | |
| Family | Fucaceae | |
| Genus | Fucus | |
| Authority | Linnaeus, 1767 | |
| Recent Synonyms | Fucus distichus distichus Powell 1957aFucus distichus anceps Linnaeus, 1767 | |
Biology
| Typical abundance | Moderate density | ||
| Male size range | Up to 30cm | ||
| Male size at maturity | 10cm | ||
| Female size range | 10cm | ||
| Female size at maturity | |||
| Growth form | Foliose | ||
| Growth rate | 10cm/year | ||
| Body flexibility | |||
| Mobility | |||
| Characteristic feeding method | Autotroph | ||
| Diet/food source | |||
| Typically feeds on | |||
| Sociability | |||
| Environmental position | Epifloral | ||
| Dependency | Independent. | ||
| Supports | No information | ||
| Is the species harmful? | Data deficient | ||
Biology information
The morphology of Fucus distichus is remarkably varied. Powell (1957a) recognised four subspecies, which were later separated into two distinct species (Fucus distichus and Fucus evanescens) by Rice and Chapman (1985). In its rock pool habit on the east coast of North America Fucus distichus is considered by Pearson & Davison (1994) to be slow growing, a poor competitor and stress intolerant. Adults of Fucus distichus are very tolerant of grazing due to a high content of phlorotannin, but germlings do not have any protection and are susceptible to grazing by littorinids.
Habitat preferences
| Physiographic preferences | Open coast |
| Biological zone preferences | Upper eulittoral |
| Substratum / habitat preferences | Bedrock, Large to very large boulders |
| Tidal strength preferences | Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.) |
| Wave exposure preferences | Extremely exposed, Very exposed |
| Salinity preferences | Full (30-40 psu), Variable (18-40 psu) |
| Depth range | Not relevant |
| Other preferences | No text entered |
| Migration Pattern | Non-migratory / resident |
Habitat Information
In Britain and Ireland, Fucus distichus has only been recorded attached to bedrock in the mid to upper eulittoral zone on exposed rocky shores in northern Scotland and Ireland. It is thought to be prevented from growing further south due to its poor tolerance of desiccation and inability to compete with plants growing further down the shore. However, on the east coast of North America, Fucus distichus is only found in rock pools and is incapable of growing on emergent rock surfaces in the mid to upper eulittoral.
Life history
Adult characteristics
| Reproductive type | Permanent (synchronous) hermaphrodite | |
| Reproductive frequency | Annual protracted | |
| Fecundity (number of eggs) | ||
| Generation time | 1-2 years | |
| Age at maturity | 2 | |
| Season | April - August | |
| Life span | 2-5 years |
Larval characteristics
| Larval/propagule type | - |
| Larval/juvenile development | Not relevant |
| Duration of larval stage | No information |
| Larval dispersal potential | No information |
| Larval settlement period | Not relevant |
Life history information
- Receptacles of Fucus distichus are initiated in December, they become ripe in April and gametes are released from April to August. Plants usually become mature when 100mm long. The whole plant dies back after reproducing and is removed from the rock by wave action during its third winter. Most plants live for 2 to 3 years (Powell, 1957b).
- Fucus distichus produces gametes of both sexes within each conceptacle. When released, ova can survive and disperse for several days. Antherozoids can only live for several hours. Self-fertilisation is thought to be high in the species and once a zygote is formed it can only be dispersed over limited distances (Rice et al., 1985).
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
| Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
| High | High | Moderate | Moderate | |
| Fucus distichus lives permanently attached to rock so would be removed upon substratum loss. The species has been observed to readily recruit to cleared areas (Ang, 1991) and has fast growth rates, so recovery rates should be high. | ||||
| High | High | Moderate | Moderate | |
| The effect of smothering depends on the state of the tide when the factor occurred. If smothering happened while the plant was emersed the whole plant would be buried underneath the sediment preventing photosynthesis. If smothering occurred while the plant was immersed the impact of smothering would be lessened because some of the fronds would escape burial. The species has been observed to readily recruit to cleared areas (Ang, 1991) and has fast growth rates, so recovery rates should be high. | ||||
| Low | Very high | Very Low | Moderate | |
| Silt may cover some of the frond surfaces reducing light available for photosynthesis and lowering growth rates. On return to normal siltation levels the normal growth rate would be quickly restored. | ||||
| No information | ||||
| High | High | Moderate | Moderate | |
| Fucus distichus is intolerant of desiccation, but the critical water content is not known. Increases in desiccation would cause the upper limit of the species distribution to become depressed. Decreases in desiccation may allow the upper limit of the species to extend up the shore. The species has been observed to readily recruit to cleared areas of the shore (Ang, 1991) and has fast growth rates, so recovery rates should be high. | ||||
| High | High | Moderate | Moderate | |
| Fucus distichus would suffer desiccation, nutrient stress and extremes of temperature when exposed to air. Increases in the period of emergence would cause the upper limit of the species distribution to become depressed. Decreases in the period of emergence may cause the species to extend further up the shore. The species has been observed to readily recruit to cleared areas (Ang, 1991) and has fast growth rates, so recovery rates should be high. | ||||
| No information | ||||
| Low | High | Low | Low | |
| Increased water flow rate may cause plants to be torn off the substratum. However, Fucus distichus appears to attach very strongly to the substratum because it lives in areas exposed to very high wave action and strong water currents. | ||||
| No information | ||||
| High | High | Moderate | Moderate | |
| Fucus distichus reaches the southern limit of its distribution in the British Isles, so would probably be very intolerant of increases in temperature. Decreases in temperature would probably have little effect and may allow the species to colonize further south. The species has been found to tolerate freezing in small rock pools in Maine (Pearson & Davison, 1994). | ||||
| No information | ||||
| Low | Very high | Very Low | Moderate | |
| Turbidity would reduce light available for photosynthesis and so lower growth rates. On return to normal turbidity levels the normal growth rate would be restored. | ||||
| No information | ||||
| Intermediate | High | Low | Low | |
| Fucus distichus has been recorded worldwide from very sheltered to very exposed conditions, but in Britain & Ireland it is mainly found on very exposed shores. A shift to more sheltered conditions may allow other fucoid species to inhabit the shore which are faster growing and would out-compete Fucus distichus. An increase in the level of wave exposure may result in plants being torn off the substratum. Provided nearby Fucus distichus populations are maintained, recovery rates should be high because the species has been observed to rapidly recruit to cleared areas (Ang, 1991). | ||||
| No information | ||||
| Tolerant | Not relevant | Not sensitive | Not relevant | |
| Seaweeds have no known mechanism for sound perception. | ||||
| Tolerant | Not relevant | Not sensitive | Not relevant | |
| Seaweeds have no known mechanism for visual perception. | ||||
| Intermediate | High | Low | Low | |
| Abrasion may damage the fronds of established seaweeds and kill germlings of Fucus distichus. Human trampling has been shown to significantly reduce the cover of fucoids on a shore (Holt et al., 1997) but trampling is unlikely to occur on the very exposed shores on which Fucus distichus lives. The species has been observed to readily recruit to cleared areas (Ang, 1991) and has fast growth rates, so recovery rates should be high. | ||||
| High | High | Moderate | Moderate | |
| Fucus distichus lives permanently attached to the substratum and upon removal it cannot re-establish an attachment. The species has been observed to readily recruit to cleared areas (Ang, 1991) and has fast growth rates, so recovery rates should be high. | ||||
Chemical pressures
| Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
| No information | Not relevant | No information | Not relevant | |
| Fucoids are generally robust in the face of chemical pollution (Holt et al., 1997), but no studies have been carried out on this particular species. | ||||
| Low | Very high | Very Low | Very low | |
| No studies have been carried out on this particular species. However, fucoids are generally robust in the face of chemical pollution and do not appear to be harmed by heavy metals (Holt et al., 1997). Intolerance is therefore, reported to be low. | ||||
| No information | Not relevant | No information | Not relevant | |
| Fucoids are generally robust in the face of chemical pollution (Holt et al., 1997), but no studies have been carried out on this particular species. | ||||
| No information | Not relevant | No information | Not relevant | |
| Insufficient information | ||||
| No information | Not relevant | No information | Not relevant | |
| Insufficient information | ||||
| Low | High | Low | Low | |
| Fucus distichus lives on shores where it is frequently drenched in rain water, so it must be able to withstand variations in salinity. The species also extends into estuaries on the coast of North America. | ||||
| No information | ||||
| No information | Not relevant | No information | Not relevant | |
| Fucus distichus is unlikely to be affected by a reduction in oxygen levels because it can generate its own oxygen by photosynthesis. However, no studies have been found to support this. | ||||
Biological pressures
| Intolerance | Recoverability | Sensitivity | Evidence/Confidence | |
| No information | Not relevant | No information | Not relevant | |
| Insufficient information | ||||
| No information | Not relevant | No information | Not relevant | |
| Insufficient information | ||||
| Intermediate | High | Low | Moderate | |
| Fucus distichus would be able to recover within five years if 50 percent of the area was cleared. The species has been observed to recruit readily to cleared areas (Ang, 1991) and has a reasonably fast growth rate. | ||||
| No information | Not relevant | No information | Not relevant | |
| Insufficient information | ||||
Additional information
Importance review
Policy/legislation
| UK Biodiversity Action Plan Priority |
Status
| National (GB) importance | Not rare/scarce | Global red list (IUCN) category | - |
Non-native
| Native | Native | ||
| Origin | Eastern Canada, Northeastern U.S.A., Northern Europe | Date Arrived | 1951 |
Importance information
-none-Bibliography
Ang, P.O., Jr., 1991. Natural dynamics of a Fucus distichus (Phaeophyta, Fucales) population: reproduction and recruitment. Marine Ecology Progress Series, 78, 71-85.
Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.
Hardy, F.G. & Guiry, M.D., 2003. A check-list and atlas of the seaweeds of Britain and Ireland. London: British Phycological Society
Holt, T.J., Hartnoll, R.G. & Hawkins, S.J., 1997. The sensitivity and vulnerability to man-induced change of selected communities: intertidal brown algal shrubs, Zostera beds and Sabellaria spinulosa reefs. English Nature, Peterborough, English Nature Research Report No. 234.
Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]
JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line] http://www.jncc.gov.uk/mermaid
Norton, T.A. (ed.), 1985. Provisional Atlas of the Marine Algae of Britain and Ireland. Huntingdon: Biological Records Centre, Institute of Terrestrial Ecology.
Pearson, G.A. & Davison, I.R., 1994. Freezing stress and osmotic dehydration in Fucus distichus (Phaeophyta): evidence for physiological similarity. Journal of Phycology, 30, 257-267.
Powell, H.T., 1957. Studies in the genus FucusL. , I. Fucus distichus L. emend. Powell Journal of the Marine Biological Association of the United Kingdom, 36, 407-431.
Powell, H.T., 1957b. Studies on the genus Fucus L. II. Distribution and ecology of Fucus distichus L. emend Powell in Britain and Ireland. Journal of the Marine Biological Association of the United Kingdom, 36, 663-693.
Rice, E.L. & Chapman, A.R.O., 1985. A numerical taxonomic study of Fucus distichus (Phaeophyta). Journal of the Marine Biological Association of the United Kingdom, 65, 433-459.
Rice, E.L., Kenchington, T.J. & Chapman, A.R.O., 1985. Intraspecific geographic-morphological variation patterns in Fucus distichus and F. evanescens. Marine Biology, 88, 207-215.
Datasets
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
OBIS (Ocean Biodiversity Information System), 2023. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2023-06-03
Royal Botanic Garden Edinburgh, 2018. Royal Botanic Garden Edinburgh Herbarium (E). Occurrence dataset: https://doi.org/10.15468/ypoair accessed via GBIF.org on 2018-10-02.
Citation
This review can be cited as:
Last Updated: 03/09/2007
