Annex I Submarine structures made by leaking gases


Annex I submarine structures made by leaking gases are rocks, pavements and pillars up to four metres high and composed of carbonate cement. This cement is produced by microbial oxidation of gases (mostly methane) that bubble up from below the seafloor. Like reefs, they provide shelter for many species such as crabs, conger eels and wolfish but they also support a unique community of chemosynthetic organisms that are able to survive on the methane and hydrogen sulphide gases. Such species include the gutless nematode Astomonema southwardorum, which is thought to have a symbiotic relationship with chemosynthetic bacteria and known only to occur at Scanner Pockmark in the North Sea.


There are two main types of submarine structure known to occur in the UK:

  1. Bubbling reefs; and
  2. Submarine structures associated with pockmarks.


There are several examples of pockmark associated submarine structures in the North Sea and bubbling reef submarine structures have been found in the Irish Sea. SACs have been selected, where possible, to include examples of both types of submarine structure and to protect the habitat throughout the full geographic range in which it occurs. More information is available on how we have identified where SACs should be located.
JNCC maintain a map that shows the location of known submarine structures made by leaking gases. It also shows areas where gas seeps are known to occur and therefore where there may be additional submarine stuctures that have not yet been found (as carbonate structures are associated with seeping methane gas). Through offshore survey, JNCC is working to confirm the presence of Annex I submarine structures in these areas. For information on the identification of SACs for submarine structures made by leaking gases within 12 nautical miles of the coast, please contact the relevant country conservation agency.

Further reading