Abstract
AbstractCold seeps can support unique faunal communities via chemosynthetic interactions fueled by seabed emissions of hydrocarbons. Additionally, cold seeps can enhance habitat complexity at the deep seafloor through the accretion of methane derived authigenic carbonates (MDAC). We examined infaunal and megafaunal community structure at high‐Arctic cold seeps through analyses of benthic samples and seafloor photographs from pockmarks exhibiting highly elevated methane concentrations in sediments and the water column at Vestnesa Ridge (VR), Svalbard (79° N). Infaunal biomass and abundance were five times higher, species richness was 2.5 times higher and diversity was 1.5 times higher at methane‐rich Vestnesa compared to a nearby control region. Seabed photos reveal different faunal associations inside, at the edge, and outside Vestnesa pockmarks. Brittle stars were the most common megafauna occurring on the soft bottom plains outside pockmarks. Microbial mats, chemosymbiotic siboglinid worms, and carbonate outcrops were prominent features inside the pockmarks, and high trophic‐level predators aggregated around these features. Our faunal data, visual observations, and measurements of sediment characteristics indicate that methane is a key environmental driver of the biological system at VR. We suggest that chemoautotrophic production enhances infaunal diversity, abundance, and biomass at the seep while MDAC create a heterogeneous deep‐sea habitat leading to aggregation of heterotrophic, conventional megafauna. Through this combination of rich infaunal and megafaunal associations, the cold seeps of VR are benthic oases compared to the surrounding high‐Arctic deep sea.
Highlights
Marine environments in the high-Arctic are characterized by intense seasonality, sub-zero bottom water temperatures, and extended periods of overlying sea ice
Downcore methane measurements from both Vestnesa Ridge (VR) and Svyatogor Ridge (SvR) were log-transformed to reduce the large variation among locations and samples and analyzed with a single-factor analysis of variance (ANOVA). Environmental characteristics Both regions, active VR and inactive SvR, exhibit oceanographic characteristics of a typical Arctic deep-sea habitat located below 1200 m of water depth, possessing dense bottom water with high salinity (34.9 psu), sub-zero temperatures (20.88C), and relatively high oxygen content (5.4 mL L21)
At active VR, the surface (0–1 cm) sediment pelite fraction was 54.6% compared to 62.5% at inactive SvR, while at 25–30 cm pelite concentrations were 82.5% and 94.5%, respectively
Summary
Marine environments in the high-Arctic are characterized by intense seasonality, sub-zero bottom water temperatures, and extended periods of overlying sea ice. Marine environments in the high-Arctic are characterized by intense seasonality, sub-zero bottom water temperatures, and extended periods of overlying sea ice These polar features set a framework for regulation of communities and ecosystems, with intense, episodic pulses of fresh organic matter interspersed among long periods of food limitation (Carroll et al 2008; Wassmann and Reigstad 2011; Boetius et al 2013; Meyer et al 2013). Deep-sea benthic communities are usually dominated by meiofauna (< 0.5 mm) (Clough et al 1997; Vanreusel et al 2000; Hoste et al 2007), with microbial activity playing a substantial role in carbon processing and remineralization (Wheeler et al 1996; Boetius et al 2013)
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