Horned wrack (Fucus ceranoides)

Fucus ceranoides.

Photographer: Dr Keith Hiscock Copyright: Dr Keith Hiscock

Detail of frond of Fucus ceranoides.

Photographer: Dr Keith Hiscock Copyright: Dr Keith Hiscock

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
Researched by Nicola White	Refereed by Dr Graham Scott
Authority	Linnaeus, 1753
Authority Linnaeus, 1753
Other common names	-	Synonyms	-
Other common names -	Synonyms -

Summary

Description

A large brown intertidal seaweed, restricted to growing in estuaries or near freshwater streams on the shore. Fucus ceranoides does not have airbladders, but the side of the fronds are often inflated.

Recorded distribution in Britain and Ireland

All coasts of Britain and Ireland

Global distribution

Spitsbergen, Iceland, Norway, Heligoland, Netherlands, Ireland, Britain, N. France, Portugal and Azores.

Habitat

Fucus ceranoides is widely distributed in north-west Europe but is only common in brackish water. It is characteristic of estuaries and is often abundant where freshwater streams run onto the shore. The species is found on the middle part of the shore, where it attaches to stones, rocks or gravel.

Depth range

Not relevant

Identifying features

Frond thin with smooth margin.
Frond fan shaped with prominent midrib.
Without air bladders but frond on either side may be inflated.
Reproductive bodies narrow, pointed fronds at ends of branches.

Additional information

No text entered

Listed by

- none -

Biology review

Taxonomy

Level	Scientific name	Common name
Phylum	Ochrophyta	Brown and yellow-green seaweeds
Brown and yellow-green seaweeds
Class	Phaeophyceae

Order	Fucales

Family	Fucaceae
Genus	Fucus
Authority	Linnaeus, 1753
Recent Synonyms

Biology

Parameter	Data
Typical abundance	High density
Male size range	Up to 60cm
Male size at maturity
Female size range	Large(>50cm)
Female size at maturity
Growth form	Foliose
Growth rate	Data deficient
Body flexibility
Mobility	Not relevant
Characteristic feeding method	Autotroph
Diet/food source
Typically feeds on	Not relevant
Sociability	No information
Environmental position	Epifloral
Dependency	Independent.
Supports	No information
Is the species harmful?	Data deficient

Biology information

Fucus ceranoides is physiologically adapted to brackish conditions. Suryono & Hardy (1997) found that growth rate was highest between 5 and 25 psu and growth was depressed at 0 and 35 psu. When cultured in high salinity they found that plant tissue decayed within 5 to 6 weeks. Khjafi & Norton (1979) recorded similar results but Baeck et al. (1992) found that Fucus ceranoides grew at full salinity for 11 weeks.

Habitat preferences

Parameter	Data
Physiographic preferences	Open coast, Strait or Sound, Sea loch or Sea lough, Ria or Voe, Estuary
Biological zone preferences	Mid eulittoral, Upper eulittoral
Substratum / habitat preferences	Bedrock, Cobbles, Gravel / shingle, Large to very large boulders, Pebbles, Small 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	Sheltered, Very sheltered
Salinity preferences	Low (<18 psu), Reduced (18-30 psu)
Depth range	Not relevant
Other preferences	No text entered
Migration Pattern	Non-migratory or resident

Habitat Information

The species is commonly found in the upper reaches of estuaries. It appears to be physiologically adapted to living in reduced salinity and exhibits its maximum growth rate at 11 psu. It is thought to be absent from fully saline sites due to an inability to compete with the faster growing fucoids, such as Fucus vesiculosus and a physiological intolerance of fully saline conditions. In areas of estuaries where salinity varies between 11 and 25 psu, Fucus ceranoides and Fucus vesiculosus can be found living together.

Life history

Adult characteristics

Parameter	Data
Reproductive type	Gonochoristic (dioecious)
Reproductive frequency	Annual episodic
Fecundity (number of eggs)	No information
Generation time	Insufficient information
Age at maturity	Insufficient information
Season	May - August
Life span	2-5 years

Larval characteristics

Parameter	Data
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

The species is usually dioecious but monoecious plants have been recorded, although it has been suggested that these are hybrids. Well developed gametangia are present on plants in southern Norway from the end of May to December. Gametes are released on daytime high tides at about full and new moon. Germlings are found from the end of May to the beginning of August. Receptacles usually drop off by October or November.

Sensitivity reviewHow is sensitivity assessed?

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 loss Benchmark. 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 Evidence Fucus ceranoides is permanently attached to the substratum, so would be removed upon substratum loss. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from some distance.	High	Moderate	Moderate	Low
Smothering [Show more] Smothering Benchmark. 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. Evidence If smothering occurred when the tide was out, the whole plant would be buried underneath the sediment, preventing photosynthesis and killing the plant. If smothering occurred when the plant was immersed, some of the frond may protrude above the sediment and not be affected. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from some distance.	High	Moderate	Moderate	Moderate
Increase in suspended sediment [Show more] Increase in suspended sediment Benchmark. 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 Evidence Fucus ceranoides is a resident of estuaries, where high levels of siltation naturally occur, so is likely to be tolerant of this factor.	Tolerant	Not relevant	Not sensitive	Moderate
Decrease in suspended sediment [Show more] Decrease in suspended sediment Benchmark. 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 Evidence			No information
Desiccation [Show more] Desiccation A normally subtidal, demersal or pelagic species including intertidal migratory or under-boulder species is continuously exposed to air and sunshine for one hour. A normally intertidal species or community is exposed to a change in desiccation equivalent to a change in position of one vertical biological zone on the shore, e.g., from upper eulittoral to the mid eulittoral or from sublittoral fringe to lower eulittoral for a period of one year. Further details. Evidence An increase in the level desiccation may result in the upper limit of the species distribution on the shore becoming depressed. A decrease in the level of desiccation may allow the species to grow further up the shore. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from some distance.	High	Moderate	Moderate	Low
Increase in emergence regime [Show more] Increase in emergence regime Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details Evidence Fucus ceranoides would suffer desiccation and nutrient stress on increased exposure to air. An increase in the period of emersion would cause the upper limit of the population to be depressed. Reduced exposure to air would enable Fucus ceranoides to extend further up the shore.	High	Moderate	Moderate	Low
Decrease in emergence regime [Show more] Decrease in emergence regime Benchmark. A one hour change in the time covered or not covered by the sea for a period of one year. Further details Evidence			No information
Increase in water flow rate [Show more] Increase in water flow rate A 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 Evidence An increase in water flow rate may tear plants of the substratum or mobilise the substratum with the plants attached. The plants with substratum may be washed away to conditions unsuitable for the growth of the species. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from some distance.	Intermediate	Moderate	Moderate	Moderate
Decrease in water flow rate [Show more] Decrease in water flow rate A 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 Evidence			No information
Increase in temperature [Show more] Increase in temperature A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges. For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details Evidence Decreases in temperature are unlikely to have any effect as the species extends to Northern Norway where temperatures are much cooler. Fucus vesiculosus, a similar species, can withstand temperatures of up to 30 degrees C, so the species is also likely to be tolerant of increases in temperature.	Low	Moderate	Low	Moderate
Decrease in temperature [Show more] Decrease in temperature A short-term, acute change in temperature; e.g., a 5°C change in the temperature range for three consecutive days. This definition includes ‘short-term’ thermal discharges. A long-term, chronic change in temperature; e.g. a 2°C change in the temperature range for a year. This definition includes ‘long term’ thermal discharges. For intertidal species or communities, the range of temperatures includes the air temperature regime for that species or community. Further details Evidence			No information
Increase in turbidity [Show more] Increase in turbidity A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details Evidence The growth rate of Fucus ceranoides may be lowered due to a reduction in the light available for photosynthesis. On return to previous turbidity levels, the growth rate would quickly return to normal.	Low	Immediate	Not sensitive	Moderate
Decrease in turbidity [Show more] Decrease in turbidity A short-term, acute change; e.g., two categories of the water clarity scale (see glossary) for one month, such as from medium to extreme turbidity. A long-term, chronic change; e.g., one category of the water clarity scale (see glossary) for one year, such as from low to medium turbidity. Further details Evidence			No information
Increase in wave exposure [Show more] Increase in wave exposure A 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 Evidence An increase in wave exposure could cause the plants to be torn off the substratum or mobilise the substratum with the plants attached. The plants with substratum may be washed away to conditions unsuitable for the growth of the species. Increased exposure would also batter the fronds against the substratum subjecting them to abrasion. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from quite far away.	Intermediate	Moderate	Moderate	Low
Decrease in wave exposure [Show more] Decrease in wave exposure A 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 Evidence			No information
Noise [Show more] Noise Underwater noise levels e.g., the regular passing of a 30-metre trawler at 100 metres or a working cutter-suction transfer dredge at 100 metres for one month during important feeding or breeding periods. Atmospheric noise levels e.g., the regular passing of a Boeing 737 passenger jet 300 metres overhead for one month during important feeding or breeding periods. Further details Evidence Seaweeds have no known mechanism for noise perception	Not relevant	Not relevant	Not relevant	Not relevant
Visual presence [Show more] Visual presence Benchmark. 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 Evidence Seaweeds have no known mechanism for visual perception	Not relevant	Not relevant	Not relevant	Not relevant
Abrasion & physical disturbance [Show more] Abrasion & physical disturbance Benchmark. 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. Evidence Abrasion may damage and remove fronds and germlings. Abrasion may result from human trampling which can significantly reduce the cover of fucoid algae on a shore (Holt et al., 1997). In general, fucoids recruit rapidly to cleared areas but populations of this species are restricted to brackish waters. Where populations are restricted to the affected area, new individuals may have to recruit in from some distance.	Intermediate	Moderate	Moderate	Low
Displacement [Show more] Displacement Benchmark. 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 Evidence Fucus ceranoides is permanently attached to the substratum so once removed a plant cannot re-establish itself. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from some distance.	High	Moderate	Moderate	Moderate

Chemical pressures

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	Intolerance	Recoverability	Sensitivity	Evidence / Confidence
Synthetic compound contamination [Show more] Synthetic compound contamination Sensitivity 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: evidence of mass mortality of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as high sensitivity; evidence of reduced abundance, or extent of a population of the species or community of interest (either short or long term) in response to a contaminant will be ranked as intermediate sensitivity; evidence of sub-lethal effects or reduced reproductive potential of a population of the species or community of interest will be assessed as low sensitivity. 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. Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Heavy metal contamination [Show more] Heavy metal contamination Evidence Fucus ceranoides accumulates heavy metals in its tissues (Barreiro et al., 1993). However, little is known of how heavy metals affect the species although fucoids are generally quite robust to chemical pollution and do not appear to be harmed by heavy metals (Holt et al., 1997). Intolerance is therefore, reported to be low. Recovery will be rapid as growth returns to normal.	Low	Very high	Very Low	Low
Hydrocarbon contamination [Show more] Hydrocarbon contamination Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Radionuclide contamination [Show more] Radionuclide contamination Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Changes in nutrient levels [Show more] Changes in nutrient levels Evidence Fucus ceranoides was found to be absent from areas of high nutrient pollution in the Tyne estuary by Suryono & Hardy (1997). In low concentrations nutrients enhance the growth rate of the alga but in high concentrations growth is stopped. In general, fucoids recruit rapidly to cleared areas, but populations of this species are restricted to brackish waters so new individuals may have to recruit in from some distance.	High	Moderate	Moderate	Moderate
Increase in salinity [Show more] Increase in salinity A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details. Evidence Fucus ceranoides is adapted to living in brackish waters. It grows fastest at 11 psu and will die when exposed to freshwater for several weeks. Suryono & Hardy (1997) and Khfaji & Norton (1979) both found that vegetative branches of Fucus ceranoides died within 5-6 weeks when grown in fully saline water. However, Baeck et al., (1992) found that Fucus ceranoides survived and grew for 11 weeks in salinities of up to 45 psu.	Intermediate	Moderate	Moderate	Moderate
Decrease in salinity [Show more] Decrease in salinity A short-term, acute change; e.g., a change of two categories from the MNCR salinity scale for one week (view glossary) such as from full to reduced. A long-term, chronic change; e.g., a change of one category from the MNCR salinity scale for one year (view glossary) such as from reduced to low. Further details. Evidence			No information
Changes in oxygenation [Show more] Changes in oxygenation Benchmark. Exposure to a dissolved oxygen concentration of 2 mg/l for one week. Further details. Evidence Insufficient information	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/parasites Benchmark. Sensitivity can only be assessed relative to a known, named disease, likely to cause partial loss of a species population or community. Further details. Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Introduction of non-native species [Show more] Introduction of non-native species Sensitivity assessed against the likely effect of the introduction of alien or non-native species in Britain or Ireland. Further details. Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Extraction of this species [Show more] Extraction of this species Benchmark. 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. Evidence Insufficient information	No information	Not relevant	No information	Not relevant
Extraction of other species [Show more] Extraction of other species Benchmark. 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. Evidence Insufficient information	No information	Not relevant	No information	Not relevant

Additional information

Importance review

Policy/legislation

- no data -

Status

National (GB) importance	-	Global red list (IUCN) category	-
National (GB) importance -
Global red list (IUCN) category -

Non-native

Parameter	Data
Native	-
Origin	-
Date Arrived	-

Importance information

-none-

Bibliography

Baeck, S., Collins, J.C. & Russell, G., 1992. Recruitment of the Baltic flora: the Fucus ceranoides enigma. Botanica Marina, 35, 53-59.
Barreiro, R., Real, C., Carballeira, A., 1993. Heavy-metal accumulation by Fucus ceranoides in a small estuary in north-west Spain. Marine Environmental Research, 36, 39-61.
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
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
Khfaji, A.K. & Norton, T.A., 1979. The effects of salinity on the distribution of Fucus ceranoides. Estuarine, Coastal and Shelf Science, 8, 433-439.
Lein, T.E., 1984. Distribution, reproduction and ecology of Fucus ceranoides L. (Phaeophyceae) in Norway. Sarsia, 60, 75-81.
Norton, T.A. (ed.), 1985. Provisional Atlas of the Marine Algae of Britain and Ireland. Huntingdon: Biological Records Centre, Institute of Terrestrial Ecology.
Suryono, C.A. & Hardy, F.G., 1997. Studies on the distribution of Fucus ceranoides L. (Phaeophyta, Fucales) in estuaries on the north-east coast of England. Transactions of the Natural History Society of Northumbria, 57, 153-168.

Datasets

Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.
Cofnod – North Wales Environmental Information Service, 2018. Miscellaneous records held on the Cofnod database. Occurrence dataset: https://doi.org/10.15468/hcgqsi accessed via GBIF.org on 2018-09-25.
Environmental Records Information Centre North East, 2018. ERIC NE Combined dataset to 2017. Occurrence dataset: http://www.ericnortheast.org.ukl accessed via NBNAtlas.org on 2018-09-38
Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01
Fife Nature Records Centre, 2018. St Andrews BioBlitz 2014. Occurrence dataset: https://doi.org/10.15468/erweal accessed via GBIF.org on 2018-09-27.
Fife Nature Records Centre, 2018. St Andrews BioBlitz 2016. Occurrence dataset: https://doi.org/10.15468/146yiz accessed via GBIF.org on 2018-09-27.
Lancashire Environment Record Network, 2018. LERN Records. Occurrence dataset: https://doi.org/10.15468/esxc9a accessed via GBIF.org on 2018-10-01.
Manx Biological Recording Partnership, 2017. Isle of Man wildlife records from 01/01/2000 to 13/02/2017. Occurrence dataset: https://doi.org/10.15468/mopwow accessed via GBIF.org on 2018-10-01.
Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1995 to 1999. Occurrence dataset: https://doi.org/10.15468/lo2tge accessed via GBIF.org on 2018-10-01.
Merseyside BioBank., 2018. Merseyside BioBank (unverified). Occurrence dataset: https://doi.org/10.15468/iou2ld accessed via GBIF.org on 2018-10-01.
NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.
OBIS (Ocean Biodiversity Information System), 2025. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2025-05-22
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.
South East Wales Biodiversity Records Centre, 2018. SEWBReC Algae and allied species (South East Wales). Occurrence dataset: https://doi.org/10.15468/55albd accessed via GBIF.org on 2018-10-02.
South East Wales Biodiversity Records Centre, 2018. Dr Mary Gillham Archive Project. Occurance dataset: http://www.sewbrec.org.uk/ accessed via NBNAtlas.org on 2018-10-02

Citation

This review can be cited as:

White, N. 2007. Fucus ceranoides Horned wrack. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 22-05-2025]. Available from: https://marlin.ac.uk/species/detail/1333

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Last Updated: 03/07/2007

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