Haig Fras is a 45 km long submarine

granitic A granitoid is a generic term for a diverse category of coarse-grained igneous rocks that consist predominantly of quartz, plagioclase, and alkali feldspar. Granitoids range from plagioclase-rich tonalites to alkali-rich syenites and from quartz- ...

rocky outcrop in the southern part of the

Celtic Sea The Celtic Sea ; cy, Y Môr Celtaidd ; kw, An Mor Keltek ; br, Ar Mor Keltiek ; french: La mer Celtique is the area of the Atlantic Ocean off the southern coast of Ireland bounded to the east by Saint George's Channel; other limits includ ...

, lying about 95 km northwest of the Isles of Scilly. It covers an area of . At one point it reaches within 38 m of the sea surface. It is protected as a

Special Area of Conservation A Special Area of Conservation (SAC) is defined in the European Union's Habitats Directive (92/43/EEC), also known as the ''Directive on the Conservation of Natural Habitats and of Wild Fauna and Flora''. They are to protect the 220 habitats and a ...

(SAC) because of the diverse fauna developed in its bedrock

reef A reef is a ridge or shoal of rock, coral or similar relatively stable material, lying beneath the surface of a natural body of water. Many reefs result from natural, abiotic processes— deposition of sand, wave erosion planing down rock o ...

habitat. It was discovered in 1962 and named by Smith and others in 1965.

Geology

The Haig Fras

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...

consists mainly of

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

, forming a WSW-ENE trending elongate intrusion. The granite outcrop is surrounded by an area of Devonian- Carboniferous

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

s. Evidence from gravity data suggests that the extent of the intrusion is greater than the observed outcrop, based on its association with a linear negative

gravity anomaly The gravity anomaly at a location on the Earth's surface is the difference between the observed value of gravity and the value predicted by a theoretical model. If the Earth were an ideal oblate spheroid of uniform density, then the gravity meas ...

. It is dated at 277 Ma, Early Permian in age, within the range of intrusion ages for the granites that make up the

Cornubian batholith The Cornubian batholith is a large mass of granite rock, formed about 280 million years ago, which lies beneath much of Devon and Cornwall, the south-western peninsula of Great Britain. The main exposed masses of granite are seen at Dartmoor, Bo ...

. Although the two intrusions have the same trend and are of similar age, they are not thought to be related. In detail, three separate outcrops have been identified using a combination of radiometric data and seabed sampling. The granite is fine to medium-grained, unlike the

megacryst In geology, a megacryst is a crystal or grain that is considerably larger than the encircling matrix. They are found in igneous and metamorphic rocks. Megacrysts can be further classified based on the nature of their origin, either as:Chapman, Carl ...

ic granite typical of the Cornubian batholith intrusions, although this may be due to the low level of sampling available. A foliated granite is locally developed as a marginal facies. The granite is thought to be cut by a

swarm Swarm behaviour, or swarming, is a collective behaviour exhibited by entities, particularly animals, of similar size which aggregate together, perhaps milling about the same spot or perhaps moving ''en masse'' or migrating in some direction. ...

of basic dykes inferred from magnetic and seismic reflection data. This swarm is interpreted to be 56 km long and 2.5 km across and at least six separate intrusive bodies have been identified. The proposed intrusions are though most likely to be of

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretace ...

age.

Fauna

Caryophyllia smithii Stokes & Broderip, 1828

The bedrock reef at Haig Fras supports a range of fauna. Jewel anemones ('' Corynactis viridis'') and Devonshire cup corals (''

Caryophyllia smithii ''Caryophyllia smithii'', the Devonshire cup coral, is a species of solitary coral in the family Caryophylliidae. It is native to the northeastern Atlantic Ocean, the North Sea and the Mediterranean Sea. There are shallow and deep-water forms wh ...

'') are found at the top of the outcrop. Encrusting sponges,

crinoid Crinoids are marine animals that make up the class Crinoidea. Crinoids that are attached to the sea bottom by a stalk in their adult form are commonly called sea lilies, while the unstalked forms are called feather stars or comatulids, which are ...

s and Ross coral ''

Pentapora fascialis ''Pentapora'' is a small genus of bryozoans in the family Bitectiporidae. Species The World Register of Marine Species lists the following species: *''Pentapora americana'' (Verrill, 1875) *'' Pentapora fascialis'' (Pallas, 1766) *'' Pentapora ...

'' are found near base of the outcrop. Mobile fauna observed include urchins such as '' Echinus esculentus'',

brittle star Brittle stars, serpent stars, or ophiuroids (; ; referring to the serpent-like arms of the brittle star) are echinoderms in the class Ophiuroidea, closely related to starfish. They crawl across the sea floor using their flexible arms for locomot ...

s and the

squat lobster Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongsi ...

Munida ''Munida'' is the largest genus of squat lobsters in the family Munididae, with over 240 species. Species *''Munida abelloi'' Macpherson, 1994 *''Munida acacia'' Ahyong, 2007 *''Munida acantha'' Macpherson, 1994 * ''Munida acola'' Macpherson, 2 ...

''.

Special area of conservation

The area of the proposed SAC is , which includes a margin of around the mapped bedrock area, derived from the maximum water depth of and an assumed length to depth ratio of a fishing warp (the cable used to tow the fishing gear) of 3:1. This is intended to protect the site from potential further damage from demersal fishing. The area was first proposed in 2004 and was included in the first tranche of candidate SACs submitted to the

European Commission The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body ...

in August 2008. It was selected on the basis of being an ''Annex I'' habitat, 1170 (reefs), in the terms of the EU

Habitats Directive The Habitats Directive (more formally known as Council Directive 92/43/EEC on the Conservation of natural habitats and of wild fauna and flora) is a directive adopted by the European Community in 1992 as a response to the Berne Convention. The E ...

References

{{coord, 50.2592, -7.7830, display=title Special Areas of Conservation in England Geology of England Celtic Sea Marine reserves of the United Kingdom