Benthic habitats of a mud volcano associated with the Queen Charlotte transform margin along northern British Columbia, Canada and Southern Alaska, United States

Abstract A newly discovered mud volcano located on the continental slope off Dixon Entrance near the international border between Canada and the United States lies in 1000 m of water and is associated with the major tectonic plate margin between the Pacific oceanic plate and the North American continental plate that is defined by the Queen Charlotte transform fault zone, which provides hard substrate habitats on a soft sediment slope. The hard substrate is manifested as carbonate slabs located in and around active gas vents at the crest and upper flanks of the volcano. The organisms associated with this mixed indurated habitat are primarily governed by depth and chemistry. Methanogenic chemosynthetic communities consisting of Phreagena soyae clams, Solemya spp. mussels, a Vestimentiferan-like tubeworm, and Beggiatoa spp. bacterial mats are the dominant chemosynthetic organisms. Anemones, shrimp, encrusting sponge, deep-sea corals (Anthomastus spp.), demosponge, serpulid, glass sponges and ophiuroids make up the sessile and epifauna, while the Thornyhead rockfish Sebastolobus sp. and the deepwater sole Embassichthys bathybius are present. Prominent gas vents, seen on echosounder profiles, may serve as proxies or indicators for the presence of similar communities along this “leaky” margin.