An ecological characterization of shallow-water cold-seep megafauna at the newly discovered Vestbrona Carbonate Field Area (VCFA), Norwegian Sea. A GIS and imagery-based analysis.
Supervisors: Arunima Sen UNIS (Svalbard), Henning Reiss (Nord Univ)
A new seep site featuring active gas release and plenty of methane-derived carbonate crusts, named Vestbrona Carbonate Field Area (VCFA), was discovered in the western Norwegian Sea (63°4’N, 6°52’E, ∿270m depth). Two portions of the area were investigated combining highresolution imagery within a Geographic Information System (GIS), free gas analysis and animal bulk stable isotope measurements, in order to characterize the site from both a biotic and abiotic perspective. Free gas was of biogenic origin and mainly composed of methane. None of the sampled taxa, across none of the trophic guilds exhibited a contribution of chemosynthetically fixed carbon to their diets, suggesting a predominantly photosynthetic source of carbon to the seep food web. The two investigated locations hosted diverse biological communities, consisting entirely of non-seep specific (background) fauna, including very fragile taxa, such as soft corals (e.g., Paragorgia arborea) and stony corals (i.e., Desmophyllum pertusum, formerly known as Lophelia pertusa). We attribute the heightened megafaunal density at the seep sites, compared to the non-seep background area, and the presence of most megafaunal taxa to habitat heterogeneity and the presence of hard substrates (i.e., methane-derived authigenic carbonates, dropstones and coral rubble), especially for the most abundant taxa, which all belonged to the phylum Porifera. Combining our data with those of megafauna datasets collected for north Atlantic (sub-Arctic) and Arctic seeps, we further suggest low to no dissimilarity between the north Atlantic and Arctic seeps. As Arctic seeps have been seen to exhibit differences from seeps in lower latitudes, (e.g., the absence of seep-endemic species and high diversity in addition to high abundance), our results thus raise the question of where the boundary between seeps with arctic characteristics and seeps with more general characteristics lies. Further studies will be needed to define this boundary.