Hydrothermal activity lowers trophic diversity in Antarctic sedimented hydrothermal vents

Abstract

17 18Sedimented hydrothermal vents are those in which hydrothermal fluid vents through sediment 19 and are among the least studied deep-sea ecosystems. We present a combination of microbial 20 and biochemical data to assess trophodynamics between and within hydrothermally active and 21 off-vent areas of the Bransfield Strait (1050 -1647m depth). Microbial composition, biomass 22 and fatty acid signatures varied widely between and within vent and non-vent sites and 23 provided evidence of diverse metabolic activity. Several species showed diverse feeding 24 strategies and occupied different trophic positions in vent and non-vent areas and stable 25 isotope values of consumers were generally not consistent with feeding structure morphology. 26Niche area and the diversity of microbial fatty acids reflected trends in species diversity and 27 was lowest at the most hydrothermally active site. Faunal utilisation of chemosynthetic activity 28 was relatively limited but was detected at both vent and non-vent sites as evidenced by carbon 29 and sulphur isotopic signatures, suggesting that the hydrothermal activity can affect 30 trophodynamics over a much wider area than previously thought. 31 32Biogeosciences Discuss., doi:10.5194/bg-2016Discuss., doi:10.5194/bg- -318, 2016 Manuscript under review for journal Biogeosciences Published: 31 August 2016 c Author(s) 2016. CC-BY 3.0 License. Section 1. Introduction 334As a result of subsurface mixing between hydrothermal fluid and ambient seawater within the 35 sediment, sedimented hydrothermal vents (SHVs) are more similar to non-hydrothermal deep-36 sea habitats than they are to high temperature, hard substratum vents (Bemis et al. 2012, 37 Bernardino et al. 2012). This creates opportunities for non-specialist, soft-sediment fauna to 38 colonise areas of chemosynthetic organic matter production, potentially offering an important 39 metabolic resource in the nutrient-limited deep-sea (Levin et al. 2009, Dowell et al. 2016. To 40 take advantage of this resource, fauna must overcome the environmental stress associated 41 with high-temperature, acidic and toxic conditions at SHVs (Levin et al. 2013, Gollner et al. 42 2015. The combination of elevated toxicity and in-situ organic matter (OM) production results 43 in a different complement of ecological niches between vents and background conditions that 44 elicits compositional changes along a productivity-toxicity gradient (Bernardino et al. 2012, 45 Gollner et al. 2015, Bell et al. 2016. Hydrothermal sediments offer different relative 46 abundances of chemosynthetic and photosynthetic organic matter, depending upon supply of 47 surface-derived primary productivity, which may vary with depth and latitude, and levels of 48 hydrothermal activity (Tarasov et al. 2005). In shallow environments (<200 m depth), where 49 production of chemosynthetic and photosynthetic organic matter sources can co-occur, 50 consumption may still favour photosynthetic OM over chemosynthetic OM as this does not 51 require adaptions to e...

Geochemistry, faunal composition and trophic structure in reducing sediments on the southwest South Georgia margin

“…0.28, figure 3 ) and an unidentified species of echiuran (mean 10.28‰ ± s.d. 0.01, figure 3 ), consistent with observations of a morphologically similar species of echiuran at a sediment-hosted hydrothermal vent in the Bransfield Strait [ 49 ]. This may indicate selective feeding strategies that favour OM that had been recycled by microbial activity, resulting in a relatively high trophic level.…”

“…The vast majority of the species that occurred in sufficient abundance for SIA were annelid taxa with no carbonate structures. A pilot study confirmed that acidification had little impact upon δ 13 C measurements, and it was considered more appropriate to preserve the integrity of nitrogen and sulfur isotope signatures [ 48 , 49 ] at the expense of a small increase in error for carbon isotope measurements. There are usually substantial differences in signatures of methanotrophic and photosynthetic C-fixation pathways, making mixed diets clearly detectable even with an additional δ 13 C error.…”

“…C/N/S measurements used the internal standards (MSAG2: (methanesulfonamide/gelatine and methionine) and the international silver sulfide standards IAEA-S1, S2 and S3. All isotope measurements included samples of freeze-dried, powdered Antimora rostrata (ANR), an external reference used in other studies of chemosynthetic ecosystems [ 49 , 50 ]. This standard was used to monitor instrumental variation between runs, instruments and studies.…”

Hydrothermal activity, functional diversity and chemoautotrophy are major drivers of seafloor carbon cycling

“…Owing to thermal decomposition of sediments, SHVs may contain high concentrations of chemosynthetic substrates, particularly methane 9 , 15 , 16 . Chemosynthetic production occurs through several pathways, such as sulphide or hydrogen oxidation or anaerobic oxidation of methane and there is now also evidence of diverse microbial lineages associated with other pathways, such as iron oxidation 17 – 20 . Fauna living in these habitats have access to both chemosynthetic and photosynthetic energy sources, while their distribution and behaviour reflect a balance between their ability to tolerate the high temperature, reducing conditions introduced by the influx of hydrothermal fluid and selectivity of the relative amounts of organic matter present 4 , 13 .…”

“…Fauna living in these habitats have access to both chemosynthetic and photosynthetic energy sources, while their distribution and behaviour reflect a balance between their ability to tolerate the high temperature, reducing conditions introduced by the influx of hydrothermal fluid and selectivity of the relative amounts of organic matter present 4 , 13 . The environmental gradients between SHVs and background sediments therefore create a range of assemblage compositions, trophic structures and pathways for in situ productivity 4 , 6 , 13 , 17 , 21 , 22 . We report here, for the first time in a sedimented vent system, how this affects energy transfers within food webs and the extent to which chemosynthetic production subsidises the diet of non-specialist fauna.…”