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

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Nomaki, H., Uejima, Y., Ogawa, N. O., Yamane, M., Watanabe, H. K., Senokuchi, R., Bernhard, J. M., Kitahashi, T., Miyairi, Y., Yokoyama, Y., Ohkouchi, N., & Shimanaga, M. Nutritional sources of meio- and macrofauna at hydrothermal vents and adjacent areas: Natural-abundance radiocarbon and stable isotope analyses. Marine Ecology Progress Series, 622, (2019): 49-65, doi:10.3354/meps13053.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 (δ13C, δ15N) and natural-abundance radiocarbon (Δ14C). Bacterial mats and Paralvinella spp. (polychaetes) collected from hydrothermal vent chimneys were enriched in 13C (up to -10‰) and depleted in 14C (-700 to -580‰). The δ13C and Δ14C 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 (δ13C: ~-24‰) and water-column plankton (Δ14C: ~40‰). In contrast, δ13C 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 Δ14C 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.We are grateful to the crews and scientists of the R/V ‘Natsushima’ and the ROV ‘Hyper-Dolphin’ of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) during the NT12-10, NT13-09 and NT14-06 cruises, and the R/V ‘Kaimei’ and the KM-ROV of JAMSTEC during the KM-ROV training cruise. We thank Yuki Iwadate for her help on sample preparations and 2 anonymous reviewers and the editor, who provided helpful comments on an earlier version of this manuscript. This work was supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan (Scientific Research C 26440246 to M.S.), the Japan Society for the Promotion of Science (Invitational fellowships for research in Japan, S14032 to J.M.B.), the WHOI Robert W. Morse Chair for Excellence in Oceanography, and The Investment in Science Fund at WHOI

Response of benthic organisms to seasonal change of organic matter deposition in the bathyal Sagami Bay, central Japan

An interdisciplinary research project was carried out to understand seasonal carbon cycling in a deep-sea ecosystem in Sagami Bay, central Japan. Temporal-changes in the chloroplastic pigment (CPE) concentration in the sediment, as well as the abundance, the biomass and the metabolic activity of benthic organisms were studied. CPE was detectable throughout the year, and its amount increased in the spring when a fluffy layer was observed on the surface of the sediment. Significant seasonal fluctuation of bacterial abundance was found, but the range was small, the maximal value being only 1.6 times larger than the minimal one. Metabolic activity did not show significant temporal difference. The abundance and biomass of metazoan meiofauna seemed to fluctuate seasonally, but ANOVA did not confirm it statistically. Our results suggest that if enough organic matter is supplied constantly, the deep-sea benthic community will be stable even though seasonality of organic matter flux associated with the spring bloom exists.Un programme de recherche interdisciplinaire a été consacré au cycle saisonnier du carbone dans un écosystème profond de la baie de Sagami, au centre du Japon. Les variations temporelles de la concentration du pigment chloroplastique (CPE) dans le sédiment ont été étudiées, ainsi que l'abondance, la biomasse et l'activité métabolique des organismes benthiques. La concentration CPE est détectable pendant toute l'année, avec une augmentation au printemps lorsqu'une couche pelucheuse est observée à la surface du sédiment. L'abondance bactérienne présente une fluctuation saisonnière significative mais de faible amplitude, avec un rapport de 1,6 entre les valeurs maximale et minimale. L'activité métabolique ne varie pas de manière significative avec le temps. L'abondance et la biomasse de la méiofaune de métazoaires semblent fluctuer avec les saisons, sans confirmation statistique Anova. Les résultats montrent que la communauté benthique profonde reste stable si l'apport de matière organique est suffisant et continu, même avec une variabilité saisonnière associée à la floraison printanière