Wednesday, 4 November 2015

Now we're in the Irish Sea, welcome to Croker Carbonate Slabs Site of Community Importance!

On the 23rd October 2015, JNCC, in partnership with the Centre for Environment, Fisheries and Aquaculture Science (Cefas), began a 14 day survey of Croker Carbonate Slabs Site of Community Importance aboard the Research Vessel (RV) Cefas Endeavour. Croker Carbonate Slabs is one of the 20 offshore candidate Special Areas of Conservation (cSAC) in UK offshore waters. The area is located in the Irish Sea, approximately 30km west of Anglesey. 
Map showing the distribution of Annex I habitat “Submarine structures made by leaking gases” within the cSAC/SCI boundary. View and download spatial data for this MPA on the JNCC UK MPA interactive mapper © JNCC, 2015.

The site is designated for Submarine structures made by leaking gases, specifically methane-derived authigenic carbonate (MDAC). These carbonate blocks and slabs form when methane rising from deep below the seabed is consumed by microbes in the seabed sediment.  The microbes create the carbonate, which acts as a cement, gluing sediment particles together to form a type of rock. The seabed habitats created by these MDAC structures support a diverse range of marine species that are absent from the surrounding seabed, which is characterised by coarse sediment.  Large carbonate blocks support a diverse range of soft corals, erect filter feeders, sponges, tube worms and anemones, whereas the flatter, pavement-like MDAC structures are colonised with scour-resistant animals such as hydroids and bryozoans.

During the survey, we will focus on gathering evidence to contribute to the development of a monitoring time-series for Croker Carbonate Slabs SCI from which the rate and direction of change in the condition of ‘submarine structures made by leaking gases’ can be inferred in the long term.

The survey aims to improve our knowledge of the distribution and spatial extent of MDAC, map the finer spatial extent of MDAC and gather further information on biological communities, including characterising the wider sediment areas found within the site.

By Alice Cornthwaite