Axial Seamount - Ecology

Ecology

In 1983, a Canadian-American collaborative expedition, named the Canadian American Seamount Expedition (CASM), visited the northwestern edge of Axial Seamount's summit caldera to investigate a persistent temperature anomaly in the region. In a series of eight dives conducted by Pisces IV, the scientists discovered a vibrant hydrothermal vent community on the leading edge of a 300 m (984 ft) fissure within the caldera. Vent temperatures were measured around 35 °C (95 °F), approximately 30 °C (86 °F) hotter than the surrounding environment. Camera tows and submersible dives through the 1980s and 1990s revealed Axial Seamount's active state, including the only known black smoker in the northwest Pacific. Three venting centers have been recognized: the original site, named CHASM; a southwestern caldera field discovered in the late 1980s, named ASHES; and a site located on its southeastern rift zone, named CASTLE. All are primarily sulfur/sulfide emitting.

The temperature and composition of Axial Seamount's hydrothermal vents changes over time, but always maintains a roughly common identity, as do the vents' individual microbial communities. Vents generally have a lower pH than the surrounding fluid, and are acidic and alkaline as a result. The temperature of the magma feeding the system is uncertain, and may vary between 300 and 550 °C (572 and 1,022 °F). Curiously, vent fluid are heavily enriched in helium, containing five times the amount of the element as similar vents in the Galapagos, and 580 times that of regular seawater.

Tube worms of the Pogonophora family thicket the largest vents on Axial Seamounts, forming colonies up to 6 m2 (65 sq ft) thick in places; smaller, less nutritious vents feed bacterial mats, smaller tube worms, and limpets. The three most common microbial groups are bacterial epsilonproteobacteria, archaeon thermophilics of the Methanococcus family, and archaeons of the Euryarchaeota family. The most common flora at Axial Seamount's hydrothermal vents is the worm Ridgeia piscesae, which is found at hydrothermal sites of all descriptions on the Juan de Fuca ridge, and is the base of Axial Seamount's hydrothermal ecosystem. Other species on the seamount include the tube worm P. palmiformis, the sea snail Lepetodrilus fucensis, the bristle worm Amphisamytha galapagensis, and the sea spider Sericosura verenae.