This inter-institutional survey, led by University College Dublin (UCD), took place on board the Marine Institute's R.V. Celtic Explorer in October/November 2015 in the Gulf of Cadiz. The aim of the survey was to assess the role of geothermal fluids emitted from points of venting (geothermal mud-volcanoes) on cold-water corals and sponge gardens in habitat diversification, biomass accumulation and biodiversity. The three planned sites were surveyed, as well as an additonal one. Mapping/CTD – prior to multi-beaming a sound velocity profile (SVP) was acquired using the CTD. At the same time as colleting SVP data the CTD was used to collect oceanic water for isotope and eDNA analyses. Multinet – a multinet was deployed to sample plankton at three different depths (same depth as the CTD water samples) both day and night to allow for assessing differences in biodiversity in the epipelagic and mesopelagic during light and dark hours. Gravity core – sediment samples were collected using a gravity corer (5m) to retrieve sediments for chemical analyses at each mud-volcano. No coring was performed at the coral control site. ROV – The Holland 1 ROV was deployed at each site to collect hard samples, acquire high-def video, ROV based cores and temperature profiles from seep areas. I. A multidisciplinary characterisation of sponge gardens, cold-water coral reefs, mud volcano associated fauna in the Gulf of Cadiz. II. Describe the ecosystem services provided by sponge gardens, cold-water coral reefs and mud volcanoes (cold seeps)s relevant to commercially significant fisheries species (e.g. blue ling, red fish, blue whiting, mackerel etc.). III. To identify biotope linkage mechanisms for the distribution of chemosynthetically derived labile organic carbon among deep-sea ecosystems (e.g. cold seeps, sponge gardens and deep-water coral reefs). IV. To advance understanding of cold-water coral reef and sponge garden development processes in sediment supply restricted settings, and thereby advance understanding of the control of sediment supply on reef attributes. V. To assess the role of linked deep-water ecosystems for carbon sequestration and climate regulation. VI. To establish the genetic connectivity among the biological communities in the Gulf of Cadiz and the wider North Atlantic in concert with international research groups (Horizon 2020, Blue Growth 1 – Improving the preservation and sustainable exploitation of Atlantic marine ecosystems). VII. To appraise the effect of localised vent-associated seawater acidity on biomineralisation. VIII. To understand the effects of underwater volcanism on rates of colonisation and the generation of habitats for marine species.