(taken from MNCR Area Summary for Fair Isle Sector 1. Shetland Islands. Christine Howson and Tim Hill 1997. Coasts and seas of the United Kingdom - MNCR series)

Introduction

Fair Isle lies about 40 km south of Sumburgh Head, mid-way between Shetland and Orkney. It is separated from Orkney by the Fair Isle Channel, which is over 100 m in depth, and lies with the rest of the Shetland Island group on a shallower platform of rock. It has some of the most exposed rocky coastline in the British Isles with numerous promontaries, geos and stacks. Inlets on the east side, North and South Haven, are protected by the dual headlands of Bu Ness and landing sites are located in these bays. There are steep cliffs on the north and west coasts whilst the south east is lower lying. Most of the island is extremely exposed to wave action although the east coast is less exposed than the Atlantic west coast. Tidal streams are of moderate strength around the headlands but are negligible elsewhere.

The island has large populations of breeding seabirds and has a bird observatory. It is an SSSI for both its geological and ornithological interest. There is a sand-eel fishing ground around the island.

Littoral

The littoral zone of Fair Isle consists almost entirely of bedrock and boulder, much of this vertical or steeply sloping, and the extremely exposed north and west coasts are bounded by cliffs. However, the coastline is indented, with numerous geos, stacks and caves and, on the east coast, two small inlets. As a result, many of the rocky shores are less steep but broken, with pools, ridges and promontaries. The headland of Bu Ness, which separates the two inlets, provides some degree of shelter and North Haven has small beaches of sand and boulder. The main landing site is located here and there is a pier and concrete slipway. Whilst the predominant biotopes are characteristic of extreme wave exposure, there are many areas of localised shelter behind rocky ridges and in the inlets and it is not uncommon to find communities more characteristic of very sheltered conditions. This leads to a patchy distribution of littoral biotopes.

Although the tidal range is only about 2 m, exposed rocky shores on Fair Isle have an extended zonation with bands of macroalgae growing up to 8 m above sea level. This has been attributed to a combination of continual swell and damp climatic conditions (Burrows et al. 1954). The most exposed open shores are dominated by the lichen Verrucaria maura in the littoral fringe. This continues downwards into the upper eulittoral where it is overlain by a blanket of the red alga Porphyra umbilicalis with a narrow band of scattered barnacles Semibalanus balanoides. Scattered Chthamalus stellatus, another barnacle species, were also found here; these and other records in Shetland represent the northern limits of the species’ known range (Powell 1954, Howson 1988). At some of these exposed sites, there is a zone of the northern fucoid Fucus distichus in the upper eulittoral but no other fucoids present. The mid eulittoral is dominated by S. balanoides and limpets Patella vulgata with clumps of small mussels Mytilus edulis whilst in the lower eulittoral there is a turf of red algae such as Mastocarpus stellatus. The kelp Alaria esculenta dominates the sublittoral fringe with large numbers of M. edulis and this zone extends to depths as great as 12 m.

In slightly less exposed conditions, fucoids are more frequent on the shore and both Fucus spiralis f. nana and Pelvetia canaliculata may be present in the upper eulittoral. The mid eulittoral has a band of barnacles and limpets and, slightly lower on the shore, these species form a mosaic with the fucoid Fucus vesiculosus f. linearis, an exposed shore form of the plant. The fucoid Fucus serratus, the thong weed Himanthalia elongata and red algae grow in the lower eulittoral whilst the sublittoral fringe has a forest of either the kelp Laminaria digitata or A. esculenta.

In localised shelter, such as behind rock ridges on the wave exposed southern tip of Fair Isle and in the more sheltered North Haven, the sheltered shore fucoids Ascophyllum nodosum and Fucus vesiculosus are found in the mid eulittoral. The unusual northern species Fucus evanescens was recorded with Fucus serratus by Powell (1975) from the lower eulittoral on the sheltered slipway in North Haven with Fucus spiralis and the green alga Blidingia minima in the upper eulittoral.

Seabirds roost on many of the rocky shores, and where this occurs there is frequently a band of the green alga Prasiola stipitata in the upper eulittoral and littoral fringe. In areas of freshwater seepage, other filamentous green algae such as Enteromorpha spp. are found. The cryptic red alga Catenella caespitosa is found in damp upper littoral crevices at a number of sites whilst the turf-like lichen Lichina pygmaea is often common in the mid and upper eulittoral. Surveys carried out in June noted few of the summer annual algae normally found on other British shores; it was suggested that this was attributable to the later onset of summer at this latitude (Burrows et al. 1954). However subsequent workers in Shetland have commented on the generally lower species diversity in the islands (Maggs 1986).

Sublittoral

Steep bedrock in the littoral zone continues into the sublittoral and, on the west coasts, extends to about 38 m where it is replaced by rippled shell gravel. On the north and south coasts, this boundary occurs shallower, at 32 m, but there are numerous rock outcrops from the gravel in deeper water. On the east coast, the rock/sediment boundary is shallower still, at about 24 to 28 m, and there is sediment from the littoral zone down to about 10 m in the sheltered harbour of North Haven. The kelp Alaria esculenta and the mussels Mytilus edulis dominate the sublittoral fringe, extending as deep as 12 m on the most exposed sites. The kelp Laminaria digitata occurs occasionally in localised shelter, such as South Haven. Kelps reach 22 m on the east of the island and at least 30 m elsewhere with dense forests of Laminaria hyperborea in the infralittoral which are particularly extensive in areas of level seabed such as South Haven. L. hyperborea is often replaced by Laminaria saccharina and Saccorhiza polyschides in the lower infralittoral. At most sites, there is a dense understorey and stipe flora with little grazings by the sea urchin Echinus esculentus in the exposed conditions although grazing is evident at some of the slightly less exposed sites on the east coast.

In the upper circalittoral, at those sites where the effects of grazing are less, there is a zone of foliose red algae with species such as Odonthalia dentata, Plocamium cartilagineum and Phycodrys rubens common along with animals such as dead men’s fingers Alcyonium digitatum and the jewel anemone Corynactis viridis. In the lower circalittoral, exposed cliff faces support A. digitatum, the calcareous tube worm Pomatoceros triqueter and the encrusting bryozoan Parasmittina trispinosa with C. viridis, the anemones Metridium senile and Sagartia elegans and clumps of the tube worm Salmacina dysteri, particularly on overhangs and gully walls. The northern spider crab Lithodes maia is also found in this situation. Sheets of the jewel anemone C. viridis and the erect bryozoan Flustra foliacea are found amongst A. digitatum on tide-swept bedrock outcrops on the north coast. Heavily grazed communities are more prevalent in the lower circalittoral than shallower and where rock gives way to boulders, notably on the south east side of the island, these are dominated by encrusting algae, the urchin E. esculentus and brittlestars. Scoured boulders amongst sand on the east coast support a similar community with the brittlestars Ophiothrix fragilis and Ophiocomina nigra, encrusting algae, the feather star Antedon bifida, A. digitatum and P. triqueter.

Caves, arches, gullies and geos are a particular feature of the shallow sublittoral around Fair Isle and these support a range of surge-tolerant biotopes. Dense algae are usually found on boulders at cave entrances where there is adequate light, with species such as Polysiphonia urceolata, Odonthalia dentata, Plocamium cartilagineum, Desmarestia aculeata and Desmarestia ligulata common. The walls support the barnacle Balanus crenatus, A. digitatum and M. senile. Further in, there is a dense sponge, bryozoan and ascidian turf on the upper parts of the walls whilst the lower parts are abraded clean. Geos are similar in many respects to caves although there is no horizontal zonation and boulders in the gully floor usually hold a forest of L. hyperborea. The sponge and ascidian turf on the walls of these gullies include such species as the sponges Myxilla incrustans and Amphilectus fucorum, C. viridis and Phellia gauspata, a surge-tolerant anemone with a northern distribution.