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Along the Atlantic European continental margin, living cold-water coral reefs occur over a wide bathymetric and hydrographical range. Focusing on 2 regions, the Celtic and the Norwegian shelves, we found that cold-water coral reefs are limited to different intermediate water masses. Measurements of the physical and geological properties showed that parameters such as temperature, salinity, dissolved oxygen content, current intensities, and different substrates vary widely without specifically impacting the distribution of living cold-water coral reefs. The habitat of living reefs within the NE Atlantic comprises a temperature-salinity field, with its lower boundary equivalent to the Intermediate Salinity Maximum (ISM). The ISM on the Celtic margin is represented by Mediterranean Outflow Water (MOW), but is replaced by Atlantic Water (AW) on the Norwegian margin. The upper limit corresponds to water mass boundaries of Eastern North Atlantic Water / MOW on the Celtic margin and Norwegian Coastal Water / AW on the Norwegian margin. Our study shows that cold-water corals in the North Atlantic tolerate a wide range of environmental conditions. However, our data indicate that living cold-water coral reefs occur within the density envelope of sigma-theta (σ Θ ) = 27.35 to 27.65 kg m -3 , thus highlighting the importance of physical boundary conditions for cold-water coral growth and distribution.

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