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Submarine mud volcanoes are important sources of methane to the water column. However, the temporal variability of their mud and methane emissions is unknown. Methane emissions were previously proposed to result from a dynamic equilibrium between upward migration and consumption at the seabed by methane-consuming microbes. Here we show non-steady-state situations of vigorous mud movement that are revealed through variations in fluid flow, seabed temperature and seafloor bathymetry. Time series data for pressure, temperature, pH and seafloor photography were collected over 431 days using a benthic observatory at the active Håkon Mosby Mud Volcano. We documented 25 pulses of hot subsurface fluids, accompanied by eruptions that changed the landscape of the mud volcano. Four major events triggered rapid sediment uplift of more than a metre in height, substantial lateral flow of muds at average velocities of 0.4 m per day, and significant emissions of methane and CO2 from the seafloor. Submarine mud volcanoes are difficult to observe from the sea surface and previous recordings at depth have been short term. Here, the authors provide the first long-term monitoring from Håkon Mosby and suggest that mud volcanoes may be more important to the global methane budget than previously thought.

Submarine canyons are known as one of the seafloor morphological features where living cold-water coral (CWC) communities develop in the Mediterranean Sea. We investigated the CWC community of the two westernmost submarine canyons of the Gulf of Lions canyon system: the Cap de Creus Canyon (CCC) and Lacaze-Duthiers Canyon (LDC). Coral associations have been studied through video material recorded by means of a manned submersible and a remotely operated vehicle. Video transects have been conducted and analyzed in order to obtain information on (1) coral bathymetric distribution and density patterns, (2) size structure of coral populations, and (3) coral colony position with respect to the substrate. Madrepora oculata was the most abundant CWC in both canyons, while Lophelia pertusa and Dendrophyllia cornigera mostly occurred as isolated colonies or in small patches. An important exception was detected in a vertical cliff in LDC where a large L. pertusa framework was documented. This is the first record of such an extended L. pertusa framework in the Mediterranean Sea. In both canyons coral populations were dominated by medium and large colonies, but the frequent presence of small-sized colonies also indicate active recruitment. The predominant coral orientation (90° and 135°) is probably driven by the current regime as well as by the sediment load transported by the current flows. In general, no clear differences were observed in the abundance and in the size structure of the CWC populations between CCC and LDC, despite large differences in particulate matter between canyons The authors acknowledge Fugro Survey, AOA Geophysics and the Universitat de Barcelona for providing the Cap de Creus Canyon multibeam bathymetry, and Serge Berne and IFREMER for providing the Lacaze-Duthiers Canyon ´multibeam bathymetry. We are indebted to the crews of the RV García del Cid and the Minibex, the JAGO team (J. Schauer and K. Hissmann) from IFM-GEOMAR (Kiel, Germany) and the scientific team onboard the Minibex during the MEDSEACAN sampling cruises; without their help it would not have been possible to carry out the field work. This work was funded by the European project LIFE+INDEMARES “Inventario y designacion de la red natura 2000 en areas marinas del estado espanol” (LIFE07/NAT/E/000732), and HERMIONE (Grant ˜Agreement Number 226354), the Spanish project DEEP CORAL (CTM2005-07756-C02-02/MAR), the Acciones Complementarias (CTM2005-24174-E, CTM2006- 27063-E/MAR, CTM2007- 28758-E/MAR), and the Agence des Aires Marines Protegées ´ (AAMP) for organizing and financing the MEDSEACAN cruises.A. G., C. O., T. M. and C. L. I. were supported by I3P and JAEDOC contract of the Consejo Superior de Investigaciones Cientificas 12 pages, 7 figures, 3 tables Peer reviewed

Investigating the relationship between deep-water coral distribution and seabed topography is important for understanding the terrain habitat selection of these species and for the development of predictive habitat models. In this study, the distribution of the deep-water gorgonians, Paragorgia arborea and Primnoa resedaeformis, in relation to terrain variables at multiple scales of 30 m, 90 m and 170 m were investigated at Røst Reef, Traena Reef and Sotbakken Reef on the Norwegian margin, with Ecological Niche Factor Analysis applied. To date, there have been few published studies investigating this aspect of gorgonian distribution. A similar correlation between the distribution of P. arborea and P. resedaeformis and each particular terrain variable was found at each study site, but the strength of the correlation between each variable and distribution differed by reef. The terrain variables of bathymetric position index (BPI) and curvature at analysis scales of 90 m or 170 m were most strongly linked to the distribution of both species at the three geographically distinct study sites. Both gorgonian species tended to inhabit local topographic highs across all three sites, particularly at Sotbakken Reef and Traena Reef, with both species observed almost exclusively on such topographic highs. The tendency for observed P. arborea to inhabit ridge crests at Røst Reef was much greater than was indicated for P. resedaeformis. This investigation identifies the terrain variables which most closely correlate with distribution of these two gorgonian species, and analyzes their terrain habitat selection; further development of predictive habitat models may be considered essential for effective management of these species.