Nutritional sources of meio- and macrofauna at hydrothermal vents and adjacent areas: natural-abundance radiocarbon and stable isotope analyses

Abstract

Deep-sea hydrothermal vents host unique marine ecosystems that rely on organic matter produced by chemoautotrophic microbes together with phytodetritus. Although meiofauna can be abundant at such vents, the small size of meiofauna limits studies on nutritional sources. Here we investigated dietary sources of meio-and macrofauna at hydrothermal vent fields in the western North Pacific using stable carbon and nitrogen isotope ratios (δ 13 C, δ 15 N) and natural-abundance radiocarbon (Δ 14 C). Bacterial mats and Paralvinella spp. (polychaetes) collected from hydrothermal vent chimneys were enriched in 13 C (up to −10 ‰) and depleted in 14 C (−700 to −580 ‰). The δ 13 C and Δ 14 C values of dirivultid copepods, endemic to hydrothermal vent chimneys, were −11 ‰ and −661 ‰, respectively, and were similar to the values in the bacterial mats and Paralvinella spp. but distinct from those of nearby non-vent sediments (δ 13 C: ~−24 ‰) and water-column plankton (Δ 14 C: ~40 ‰). In contrast, δ 13 C values of nematodes from vent chimneys were similar to those of non-vent sites (ca. −25 ‰). Results suggest that dirivultids relied on vent chimney bacterial mats as their nutritional source, whereas vent nematodes did not obtain significant nutrient amounts from the chemolithoautotrophic microbes. The Δ 14 C values of Neoverruca intermedia (vent barnacle) suggest they gain nutrition from chemoautotrophic microbes, but the source of inorganic carbon was diluted with bottom water much more than those of the Paralvinella habitat, reflecting Neoverruca's more distant distribution from active venting. The combination of stable and radioisotope analyses on hydrothermal vent organisms provides valuable information on their nutritional sources and, hence, their adaptive ecology to chemosynthesis-based ecosystems.

Integrative taxonomy revisits the ontogeny and trophic niches ofRimicarisvent shrimps

“…Recently, Nomaki et al . [ 50 ] revealed that natural abundance radiocarbon content (Δ 14 C) clearly shifted from lower ratios in organisms living in bottom waters or at vents to higher ratios in water column plankton in the area of the Izu-Ogasawara Arc. Δ 14 C could therefore be used as an ecological tracer to provide additional hints on the habitat of dispersing Rimicaris larvae.…”

“…They may stay close to the seafloor with other deep-sea epibenthic fauna, or live several hundreds of metres above the vent fields, while consuming, in both scenarios, organic carbon sinking down from the surface. Recently, Nomaki et al [50] revealed that natural abundance radiocarbon content (Δ 14 C) clearly shifted from lower ratios in organisms living in bottom waters or at vents to higher ratios in water column plankton in the area of the Izu-Ogasawara Arc. Δ 14 C could therefore be used as an ecological tracer to provide additional hints on the habitat of dispersing Rimicaris larvae.…”

Structure and Connectivity of Hydrothermal Vent Communities Along the Mid-Ocean Ridges in the West Indian Ocean: A Review

“…Next, observations on animal behavior are too insufficient to infer trophic interactions with confidence. Third, the communities at the meio-and microscale, where many trophic interactions are expected to happen (Schmid-Araya and Schmid, 2000;Zekely et al, 2006;Nomaki et al, 2008Nomaki et al, , 2019Ptatscheck et al, 2020), remain virtually undescribed. Only one study characterizing the Indian vent meiofaunal communities has been published to date (Kang and Kim, 2021).…”

Simple harpacticoid composition observed at deep hydrothermal vent sites on sea knoll calderas in the North-west Pacific

“…In contrast, Harpacticoida, another highly abundant copepod taxon, showed decreased frequencies with increasing δ 13 C values at vent sites in those knolls (Senokuchi et al, 2018). The δ 13 C values of copepod tissues also suggest that dirivultids rely on vent chimney bacteria as their nutritional source (Nomaki et al, 2019). These results strongly suggest that chemoautotrophic food resource availability is the key factor controlling vent copepod distributions, at least at higher taxonomic levels.…”

“…The samples used in this study were collected using the research vessel (RV) 'Natsushima' (cruises NT12-10 in 2012, NT13-09 in 2013 and NT14-06 in 2014; all cruises in April), which visited three adjacent knoll-associated calderas with known active hydrothermal vent systems: Bayonnaise Knoll, Myojin-sho Caldera and Myojin Knoll (Figure 1, Table 1). Details of the sampling sites and procedures have been reported previously (Senokuchi et al, 2018;Nomaki et al, 2019). In brief, samples were collected using the remotely operated vehicle (ROV) 'Hyper-Dolphin'.…”