Comparative Composition, Diversity and Trophic Ecology of Sediment Macrofauna at Vents, Seeps and Organic Falls

Abstract

Sediments associated with hydrothermal venting, methane seepage and large organic falls such as whale, wood and plant detritus create deep-sea networks of soft-sediment habitats fueled, at least in part, by the oxidation of reduced chemicals. Biological studies at deep-sea vents, seeps and organic falls have looked at macrofaunal taxa, but there has yet to be a systematic comparison of the community-level attributes of sediment macrobenthos in various reducing ecosystems. Here we review key similarities and differences in the sediment-dwelling assemblages of each system with the goals of (1) generating a predictive framework for the exploration and study of newly identified reducing habitats, and (2) identifying taxa and communities that overlap across ecosystems. We show that deep-sea seep, vent and organic-fall sediments are highly heterogeneous. They sustain different geochemical and microbial processes that are reflected in a complex mosaic of habitats inhabited by a mixture of specialist (heterotrophic and symbiont-associated) and background fauna. Community-level comparisons reveal that vent, seep and organic-fall macrofauna are very distinct in terms of composition at the family level, although they share many dominant taxa among these highly sulphidic habitats. Stress gradients are good predictors of macrofaunal diversity at some sites, but habitat heterogeneity and facilitation often modify community structure. The biogeochemical differences across ecosystems and within habitats result in wide differences in organic utilization (i.e., food sources) and in the prevalence of chemosynthesis-derived nutrition. In the Pacific, vents, seeps and organic-falls exhibit distinct macrofaunal assemblages at broad-scales contributing to ß diversity. This has important implications for the conservation of reducing ecosystems, which face growing threats from human activities.

Hydrothermal activity lowers trophic diversity in Antarctic sedimented hydrothermal vents

“…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).…”

“…Sedimented vents may 70 present several sources of organic matter to consumers (Bernardino et al 2012, Sweetman et 71 al. 2013) and the diverse microbial assemblages can support a variety of reaction pathways, 72 including methane oxidation, sulphide oxidation, sulphate reduction and nitrogen fixation 73 (Teske et al 2002, Dekas et al 2009, Frank et al 2013, Jaeschke et al 2014, Wu et al 2014, 74 Inskeep et al 2015, McKay et al 2015.…”

“…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…”

Comparative Study of Guaymas Basin Microbiomes: Cold Seeps vs. Hydrothermal Vents Sediments

“…Comparative studies of faunal and microbial community structure between hydrothermal vent and cold seep ecosystems demonstrated functional and phylogenetic similarities but also numerous distinctive features (Sibuet and Olu, 1998;Tunnicliffe et al, 1998;Bernardino et al, 2012;Portail et al, 2016). These differences may arise from specific ecological niches related to the nature of fluids.…”

<i>Spinaxinus</i> (Bivalvia: Thyasiroidea) from sulfide biogenerators in the Gulf of Mexico and hydrothermal vents in the Fiji Back Arc: chemosymbiosis and taxonomy

“…The faunal compositions of organic falls and those at vents/seeps are reported to be distinct (Bernardino et al 2012), suggesting that different environmental markers are present. However, one well-studied thyasirid (T. sarsi) reveals that such conservatism is not universal.…”