Annex I Submarine structures made by leaking gases consist of
rocks, pavements and pillars up to 4 m high. They are formed of
carbonate cement resulting from microbial oxidation of gas, mainly
methane (most likely to have originated from the decomposition of
fossil plant materials). These carbonate formations are
interspersed with gas vents that intermittently release gas.
As well as providing a potentially favourable, sheltered
habitat for a variety of marine species, submarine structures
associated with active gas seeps may be of ecological significance
because i) of the use of methane and its by-product, hydrogen
sulphide, by chemosynthetic microorganisms; ii) the carbonate
structures provide increased habitat diversity and a hard
substratum suitable for colonisation by certain benthic organisms
(Judd, 2001) . Further information about
Annex I Submarine structures made by leaking gases is
provided on JNCC's website, and the formal
EU interpretation of this habitat is available in the
EU's
Interpretation
Manual of European Habitats.
Offshore sites should be selected to represent the main
variants of this habitat occurring offshore, having regard to
geographical range (Hopkins & Buck 1995). Two main types of
Submarine structures made by leaking gases have been identified
and, where possible, sites will be selected to encompass
both these variants:
- ‘Bubbling reefs’
- Submarine structures associated with ‘pockmarks’.
A number of occurrences of this habitat have been discovered
in the North Sea in a large area of shallow gas where pockmarks
caused by gas seepage are a common occurrence. The extent of
the habitat is small and composed of blocks and pavements of
carbonate within and adjacent to pockmark depressions.
More recently, submarine structures made by leaking gases have been
found in the Irish Sea. These are not associated with
pockmark features and are more closely aligned with the “bubbling
reef” variant, as described by the Interpretation Manual of
European Habitats.
The location of known areas of
Submarine structures made by leaking gases in UK waters is shown in
the map below. Through offshore biological and
geomorphological survey, JNCC is working to confirm Annex I
Submarine structures presence and identify those sites which
merit selection as SACs. For information on the identification
of SACs for Annex I Submarine structures made by leaking gases
within 12nm of the coast, please contact the
relevant country conservation
agency (Natural England (formally English Nature), Northern
Ireland Environment Agency, Scottish Natural Heritage or the
Countryside Council for Wales).
Jensen P, Aagaard I, Burke RA, Dando PR,
Jørgensen NO, Kuijpers A, Laier T, O´Hara SCM &
Schmaljohann R (1992) 'Bubbling Reefs' in the Kattegat: submarine
landscapes of carbonate-cemented rocks support a diverse ecosystem
at methane seeps. Marine Ecology, Progress Series,
83, 103-112.
Judd, A.G. 2001. Pockmarks in the UK Sector of the North
Sea. Technical report (TR_002) produced for Strategic
Environmental Assessment - SEA2. UK: Department of Trade and
Industry.