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

摘要

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 (delta C-13, delta N-15) and natural-abundance radiocarbon (Delta C-14). Bacterial mats and Paralvinella spp. (polychaetes) collected from hydrothermal vent chimneys were enriched in C-13 (up to -10 parts per thousand) and depleted in C-14 (-700 to -580 parts per thousand). The delta C-13 and Delta C-14 values of dirivultid copepods, endemic to hydrothermal vent chimneys, were -11 parts per thousand and -661 parts per thousand, respectively, and were similar to the values in the bacterial mats and Paralvinella spp. but distinct from those of nearby non-vent sediments (delta C-13: similar to-24 parts per thousand) and water-column plankton (Delta C-14: similar to 40 parts per thousand). In contrast, delta C-13 values of nematodes from vent chimneys were similar to those of non-vent sites (ca. -25 parts per thousand). 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 Delta C-14 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.