Two scleractinian cold-water corals, Desmophyllum dianthus and Caryophyllia huinayensis are abundant on hard substrate, below 18 m depth, throughout the entire fjord Comau in Northern Patagonia, Chile. At “X-Huinay” (42º 23.276’ S, 72º 27.657’ W) on the western side of the central fjord, a recent mass mortality of D. dianthus occurred, while C. huinayensis survived. H2S seeps here support the formation of filamentous chemosynthetic bacterial mats. At this site, sulfide concentrations of up to 100 higher than normal ambient water values have been measured.