Vents & Seeps

Hydrothermal vents are areas where hot seawater enriched in reduced compounds, such as hydrogen sulphide, streams out of the seafloor. Dissolved minerals are deposited where the fluid streams out, forming chimney-like structures, and the fluid itself looks like smoke. Hydrothermal fluids can have temperatures of up to 350°C, and the color of the fluid varies between black to whiteish depending on the temperature and the mineral composition. At cold seeps, hydrocarbon-rich fluids seep out of the seafloor at, or close to ambient seawater temperatures. Hydrothermal vents are usually found on mid-ocean ridges, while cold seeps are often found along continental margins.

The vent and seep ecosystems have in common that primary production is performed by bacteria and archaea which get their energy from the reduced compounds in the fluids. This is called chemosynthesis, and forms the basis for an ecosystem of specialized animals. Animals living at vents or seeps can get nutrients from chemosynthetic microorganisms either by feeding on them, or through symbiosis. Symbiosis is a close relationship between the microorganism (the symbiont) and the host, where the host makes sure the symbiont has suitable conditions to perform chemosynthesis, and the symbiont provides nutrients to the host. An example of symbiosis at arctic vents is found in the amphipod Exitomelita sigynae, which has a dense layer of bacteria on their gills that probably supplies them with nutrients from chemosynthesis (Tandberg et al., 2012).

The animals living at vents and seeps have to tolerate extreme environmental conditions such as high temperatures (at vents), low pH and toxic chemicals such as hydrogen sulphide and heavy metals. The reward for tolerating these challenging conditions is a high abundance of food, compared to the food-poor deep sea surrounding the vents. Most of the animals living at hydrothermal vents are endemic to these habitats, and not found outside the vent environment. However, some vent fauna is shared with other chemosynthesis-based ecosystems, such as cold seeps.

Hydrothermal vents on the Arctic Mid-Ocean Ridge (AMOR) does not have any of the large, charismatic species of the Atlantic and Pacific vents, such as gigant tube worms or bivalves. However, looking closer there is a unique and specialized fauna with links both to the Atlantic and the Pacific and even all the way to the Antarctic (Pedersen et al., 2010; Kongsrud et al., 2016, Eilertsen et al., 2018). There are also several shared species between hydrothermal vents and cold seeps in the region, such as the siboglinid tube worm Sclerolinum contortum and the rissoid gastropod Pseudosetia cf. griegi. However, the work on vent and seep faunas in Norwegian waters have so far focused on a few selected taxa, and complete faunal inventories are lacking.

Eilertsen, M. H., Georgieva, M. N., Kongsrud, J. A., Linse, K., Wiklund, H., Glover, A. G., et al. (2018). Genetic connectivity from the Arctic to the Antarctic: Sclerolinum contortum and Nicomache lokii (Annelida) are both widespread in reducing environments. Scientific Reports 8, 4810. doi:10.1038/s41598-018-23076-0.
Kongsrud, J. A., Eilertsen, M. H., Alvestad, T., Kongshavn, K., and Rapp, H. T. (2017). New species of Ampharetidae (Annelida: Polychaeta) from the Arctic Loki Castle vent field. Deep Sea Research Part II: Topical Studies in Oceanography 137, 232–245. doi:10.1016/j.dsr2.2016.08.015.
Pedersen, R. B., Rapp, H. T., Thorseth, I. H., Lilley, M. D., Barriga, F. J. A. S., Baumberger, T., et al. (2010). Discovery of a black smoker vent field and vent fauna at the Arctic Mid-Ocean Ridge. Nature Communications 1, 126. doi:10.1038/ncomms1124.
Tandberg, A. H., Rapp, H. T., Schander, C., Vader, W., Sweetman, A. K., and Berge, J. (2012). Exitomelita sigynae gen. et sp. nov.: a new amphipod from the Arctic Loki Castle vent field with potential gill ectosymbionts. Polar Biol 35, 705–716. doi:10.1007/s00300-011-1115-x.