Abstract
Sedimented hydrothermal vents, where hot, mineral-rich water flows through sediment, are poorly understood globally, both in their distribution and the ecology of individual vent fields. We explored macrofaunal community ecology at a sediment-hosted hydrothermal vent in the Southern Ocean. This is the first such study of these ecosystems outside of the Pacific and the furthest south (62˚S) of any vent system studied. Sedimentary fauna were sampled in four areas of the Bransfield Strait (Southern Ocean), with the aim of contrasting community structure between vent and non-vent sites. Macrofaunal assemblages were clearly distinct between vent and non-vent sites, and diversity, richness and density declined towards maximum hydrothermal activity. This variation is in contrast to observations from similar systems in the Pacific and demonstrates the influence of factors other than chemosynthetic primary productivity in structuring infauna at deep-sea vent communities. Vent endemic fauna had limited abundance and were represented by a single siboglinid species at hydrothermally active areas, meaning that that the majority of local biota were those also found in other areas. Several taxa occupied all sampling stations but there were large differences in their relative abundances, suggesting communities were structured by niche variation rather than dispersal ability.
Highlights
Deep-sea hydrothermal vent fields are under imminent threat from mineral extraction (Petersen et al, 2004; Van Dover, 2010), creating an imperative to understand these environments so that their inhabitants may be effectively conserved
The vast majority of deep-sea hydrothermal vent research has focused on high-temperature vents, which are typically dominated by vent endemic species (e.g., Rogers et al, 2012)
We explore the influence of environmental gradients upon community composition and results are quantitatively compared to Bernardino et al (2012)’s conceptual models of abundance, diversity and proportions of vent endemic fauna, using a measure of environmental distance
Summary
Deep-sea hydrothermal vent fields are under imminent threat from mineral extraction (Petersen et al, 2004; Van Dover, 2010), creating an imperative to understand these environments so that their inhabitants may be effectively conserved. At SHVs, and in some diffuse venting areas around high-temperature vents, hydrothermal fluid mixes with ambient seawater beneath the seafloor (Bemis et al, 2012) and, in terms of oceanic heat flux, may be more significant than high temperature vents (Larson et al, 2015). The mixing of the hydrothermal fluid with ambient seawater means that it cools too slowly to precipitate mineral structures, creating an environment comprised of hot (generally 10–100◦C above ambient), high porosity sediment, typically with high levels of hydrogen sulfide, methane, and reduced metals, such. Hydrothermal sites in the Bransfield Strait (Southern Ocean) potentially provide a stepping stone between chemosynthetic communities in the Atlantic, Indian, and Pacific Oceans (Rogers et al, 2012; Roterman et al, 2013) as well as providing an interesting site to explore how ambient deep Southern Ocean benthos respond to reducing environments
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