Site details

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United kingdom
5 stars - Fully protected as a national park or Natura 2000 site by national legislation
ATBI Reference Site

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Panorama from Guthers island. Photo: J T Davey

Synoptic description of site:

An archipelago of 5 inhabited islands and over 300 smaller islands, islets and rocks, 43 km WSW of the western extremity of the Cornish peninsula, mainland UK.

Extensive description of site:

The Isles of Scilly comprise five inhabited islands and more than 300 other uninhabited islands islets and rocks, situated some 40 km west of the SW tip of mainland Britain. The total area delimited by these islands is approximately 95 km2. They have been described as “the only Lusitanian oceanic archipelago in Europe” (English Nature 1994), and the high national importance of these Isles is now recognised by their high conservation status. Predominantly west-to-east ocean currents and an almost total lack of freshwater runoff results in uniform salinity and low turbidity; the alga Laminaria ochroleuca, which occurs in dense stands, has been recorded at depths of up to 30m. Habitat diversity within the archipelago is high, and many sites have a complex array of habitat types in a small area. Wave exposure varies from extremely exposed to very sheltered, often within a short distance. All habitats within the region of SW England are present, except for pure muddy intertidal and subtidal sediments. However, in SW Britain such sediments are usually associated with estuaries, which are in turn associated with high turbidity and low salinity which are considered undesirable features for a BIOMARE Flagship Site typifying the region. The rocky shores and boulder fields are a designated habitat (“reefs”) for the Isles of Scilly Special Area of Conservation, as are the extensive intertidal sand-flats and sand beaches. Sublittoral rocky habitats are also designated as part of the “reef” habitat. They range from extremely exposed to very sheltered, and clear water results in extensive kelp forests. Sublittoral sediments range from coarse sand and gravel to fine sand to muddy gravel, which are again a designated habitat (“sandbanks which are slightly covered by sea water all the time”) for the SAC. Seagrass beds (of Zostera marina) are extensive, the largest in southern Britain, and have a particularly interesting fauna and flora.

Habitats present:
Littoral XX
Seagrass bedsX

Description of fauna and flora:

The biota has a number of special features. Several species from southern Europe and the Mediterranean are found on Scilly and nowhere else in Britain, and the Islands have more benthic species defined as ‘nationally rare’ and ‘nationally scarce’ than any other locality in SW Britain. The Scillonian marine fauna and flora has received sporadic attention from amateur and professional collectors and recorders over the past century and a half. Comprehensive inventories of many components of the biota have been published, most of them in a dedicated series of papers in the Journal of Natural History: these include Diatoms, Macroalgae, Foraminifera, Cnidaria, Ctenophora, Digenea, free-living Nematoda, Gastrotricha, Polychaeta, Tardigrada, Acari, Crustacea (Eucarida, Ostracoda, Copepoda: Harpacticoida, Mysidacea,), Pycnogonida, Mollusca, Bryozoa, Entoprocta, Echinodermata. Enteropneusta, Ascidiacea, Thaliacea, Larvacea and Cephalochordata. In addition, there are around 200 other publications relating specifically to the biodiversity or natural environment of Scilly. The longest formal time series data are for zooplankton and phytoplankton. The Continuous Plankton Recorder Survey (CPR) has had routes passing through the coastal waters of Scilly every year from 1950 to the present, averaging 40 samples per year. In connection with the EU Special Area of Conservation (SAC) status, English Nature has initiated regular monitoring programmes for the sandflats, reefs and seagrass beds.

Pristiness: High


No industry. No freshwater inflows (low turbidity - kelp grows to a depth of 30m - and no reduction in salinity).

Human impact:

There is no industrial pollution, mining, dumping or dredging, and potentially harmful agricultural runoff is negligible due to strict legislation. The current population is 2057 and this remains more of less static. There is a small shellfishery, potting or using large mesh fixed nets for crabs and lobsters, and only one small (8m) trawler. The use of vessels exceeding 11 metres overall length for the removal of fish from within 6 miles round the Islands is prohibited and strictly enforced.


The islands are accessible by three means of public transport; passenger ferry, helicopter and fixed wing aircraft. All inhabited islands can be reached from the main centre, Hugh Town, by daily services of local launches, and all shores are accessible via coastal footpaths. Local boats that are capable of all normal requirements for biodiversity work may be hired for working on the uninhabited islands and offshore. The distance from the Islands to the nearest fully equipped marine research laboratories in Plymouth is approximately 160 km ‘as the crow flies’, and normally takes about 3 hours. There is no laboratory on the islands purposely built or equipped for marine biological work, although active steps are being taken to rectify this situation. Various temporary premises are available for use ranging from the size of small rooms suitable for one or two researchers to the facilities of the local secondary school where field courses of 30 or more students operate. The facilities for SCUBA diving are very comprehensive. Several fully qualified operators offer all facilities: dive-boats, equipment, compressors, and local knowledge of dive-sites. All forms of housing, ranging from self-catering cottages to 4 star hotels, are available. Most hotels close in winter, but guesthouses and self-catering accommodation are available throughout the year.

Available database and website:

Records of marine species belonging to all taxa are incorporated in the ERCCIS database, in EXCEL on CD-ROM, which is now under the aegis of the Environmental Centre for Cornwall and the Isles of Scilly. This includes data on abundance, habitat type, collectors names, dates etc. CPR data for Scillonian coastal waters can be obtained via the SAHFOS website


Commitment and ongoing research:

Scilly is the major focus for the Plymouth Marine Laboratory’s programme of biodiversity research. English Nature has statutory responsibility for surveying and monitoring the marine biota of the islands. Seventeen scientists spend a significant proportion of their time on this research, and in addition there are numerous sub-contractors, amateurs and students also undertaking marine biological work on the islands. The Plymouth Marine Laboratory has an agreed science plan and specifically allocated budget for biodiversity work on the Isles of Scilly. English Nature has statutory responsibility for monitoring NATURA 2000 habitats.