One of the most extensive seepage areas of the North-East Atlantic was discovered in the bathyal bottoms of the Gulf of Cadiz during the nineteen nineties. A variety of seafloor structures, formed as a consequence of the gas-saturated fluid seeping, have been recorded since then in this area. These include more than sixty mud volcanoes  located between 300 and 1200 m depth.  Some microorganisms, living in fluid venting areas like this, can indirectly shape this already peculiar deep environment. They consume the hydrocarbon gases released from the seabed, and this process leads to precipitation of carbonates, forming new structures– called authigenic carbonates –which are available for colonization by other benthic organisms. Several oceanographic campaigns provided data on the characteristics of mud volcano habitats, included remotely operated underwater vehicle (ROV) transects and the collection of sponge samples by beam trawl along 8 mud volcanoes between 380 and 1146 m depth.

Our study had two main objectives:

• To identify the sponge species collected from the mud volcanoes.

• To test if some features related to the mud volcano habitat affect its sponge richness and abundance.

Our study has benefited from funds of different EC grants (LIFE + INDEMARES, LIFE-IP INTEMARES and H2020 SponGES) and from a Spanish Ministry of Economy and Competitiveness grant.

The article Deep-water sponge fauna from the mud volcanoes of the Gulf of Cadiz (North Atlantic, Spain) is available Open Access in the Journal of the Marine Biological Association