Faunal trophic structure at hydrothermal vents on the southern Mohn’s Ridge, Arctic Ocean

Abstract

We explore the trophic ecology of heterotrophic fauna associated with a high temperature (HT) vent, 2 low temperature vents, a 'near-HT vent' habitat and a non-vent site situated at upper bathyal depths on the southern Mohn's Ridge in the Arctic Ocean. Only a single taxon (the gastropod Pseudosetia griegi ) was found at the high temperature vent habitat. Their mean δ 13 C values were significantly lighter than conspecifics from a low temperature vent habitat within the same vent field, reflecting the incorporation of sulfide oxidizing bacteria into the biomass of the animals. The majority of fauna from the low temperature, near-HT, and non-vent habitats had isotopic signatures indicative of assimilation of photosynthetic material. However, we found remarkably diverse isotopic compositions among the fauna sampled here, with a small sub-set of fauna at each site possessing C and N isotopic signatures indicative of incorporation of chemosynthetic production. Moreover, when isotopic signatures of similar taxa were compared from the same sample, δ 13 C signatures suggested a high degree of trophic complexity can exist over relatively small spatial scales at vent habitats on the southern Mohn's Ridge. The high contribution of photosynthetic food material to faunal diets and variability in food types may result from the upper bathyal venting depth and sedimentary nature of the vents. We hypothesize that the upper bathyal depth of active venting may lead to iron enhancement of surface photosynthetic production, especially in high nutrient areas, which ultimately sinks to the seabed where it is incorporated by fauna around the vents. KEY WORDS: Hydrothermal vents · Fauna · Stable isotopes · Mixing models · Southern Mohn's RidgeResale or republication not permitted without written consent of the publisher

Hydrothermal activity lowers trophic diversity in Antarctic sedimented hydrothermal vents

“…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 environmental toxicity (Kharlamenko et al 1995, Tarasov et al 2005, 52 Sellanes et al 2011. Limited information of trophodynamics at deep-sea SHVs indicate that 53 diet composition estimates vary widely between taxa, ranging between 0 -87 % contribution 54 from chemosynthetic OM (Sweetman et al 2013). Thus, understanding of the significance of 55 chemosynthetic activity in these settings is very limited.…”

“…Microbial aggregations are commonly visible on the sediment surface at SHVs (Levin et al 67 2009, Aquilina et al 2013, Sweetman et al 2013, Dowell et al 2016) but active communities 68 are distributed throughout the underlying sediment layers, occupying a wide range of 69 geochemical and thermal niches (reviewed by Teske et al 2014). Sedimented vents may 70 present several sources of organic matter to consumers (Bernardino et al 2012, Sweetman et 71 al.…”

“…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.…”

“…56 57 Biogeosciences Discuss., doi:10.5194/bg-2016Discuss., doi:10.5194/bg- -318, 2016 Manuscript under review for journal Biogeosciences with hydrothermal activity provides thermodynamic benefits and constraints to microbial 63 community assembly (Kallmeyer & Boetius 2004, Teske et al 2014) but also accelerates the 64 degradation of organic matter, giving rise to a wide variety of compounds, including 65 hydrocarbons and organic acids (Martens 1990, Whiticar & Suess 1990, Dowell et al 2016. 66Microbial aggregations are commonly visible on the sediment surface at SHVs (Levin et al 67 2009, Aquilina et al 2013, Sweetman et al 2013, Dowell et al 2016) but active communities 68 are distributed throughout the underlying sediment layers, occupying a wide range of 69 geochemical and thermal niches (reviewed by Teske et al 2014). Sedimented vents may 70 present several sources of organic matter to consumers (Bernardino et al 2012, Sweetman et 71 al.…”

“…These 85 species are known to harbour chemoautotrophic endosymbionts (Schmaljohann et al 1990, 86 Gebruk et al 2003, Thornhill et al 2008, Eichinger et al 2013, Rodrigues et al 2013. Stable 87 isotope analysis (SIA) is a powerful tool to assess spatial and temporal patterns in faunal 88 behaviour and has been used to study trophodynamics and resource partitioning in other SHVs 89 (Southward et al 2001, Levin et al 2009, Soto 2009, Levin et al 2012, Sweetman et al 2013. 90…”