Seaweed survey of the Outer Hebrides

The executive summary from a report for the Crown Estate detailing the results of a survey of the Outer Hebrides conducted in July/Augst 2012 by Juliet Brodie and Jo Wilbraham.

Executive Summary

A shore survey of the red (Rhodophyta), brown (Phaeophyceae) and green (Chlorophyta) seaweeds undertaken between the 30th July and 7th August 2012 at 19 sites in North and South Uist, Harris and Lewis in the Outer Hebrides, yielded 525 records and c. 128 species – approximately 20% of the UK seaweed flora. A literature search of seaweed research in the Outer Hebrides from 1844 to the present revealed 389 taxon names – over 60% of the UK flora. Four hundred and ninety specimens were collected and preserved for incorporation into the algal herbarium at the Natural History Museum. The number of species recorded for saltmarshes and other sheltered sites dominated by large brown fucoids ranged from 4 to 12, and for open coasts between 41 and 65. The most commonly recorded species were the reds Chondrus crispus and Vertebrata lanosa (the latter epiphytic on Ascophyllum nodosum), the browns Fucus spiralis, F. vesiculosus and Pelvetia canaliculata, and the green Cladophora rupestris. Five non-native species were recorded: reds Asparagopsis armata (Falkenbergia sporophyte phase), Bonnemaisonia hamifera (Trailliella sporophyte phase), Pyropia leucosticta, brown Colpomenia peregrina and green Codium fragile subsp. fragile. The highly invasive brown species Sargassum muticum was not encountered at the sites studied but it has been reported in 2012 from Benbecula. A comparison of the species composition for sites Geodh’an Faraidh and Port Geiraha, previously studied in 1971, indicated that although the overall number was similar only c. 20% were the same species. The following genera of seaweed were highlighted as taxonomically in need of study for the area: the reds Osmundea, Ceramium and Polysiphonia, browns Sphacelaria and Fucus (notably hybrids) and the greens Cladophora, and Ulva. This survey provides a new baseline for the Outer Hebrides and it confirms the importance of the area for its seaweed diversity and resource. Recommendations include: i) monitoring should be undertaken in parallel with any increased harvesting in order to monitor impact on seaweed diversity; ii) detailed seaweed surveys should be undertaken at fixed sites at regular intervals to study long term change; iii) several genera of seaweed require taxonomic studies and iv) collections should be made during survey work and deposited in national herbaria as a verifiable source of data for future reference.


Brodie J & Wilbraham J (2012) Seaweed survey of the Outer Hebrides. A report for the Crown Estate. (PDF)

Brodie & Wilbraham 2012


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