Nematode feeding strategies and the fate of dissolved organic matter carbon in different deep-sea sedimentary environments

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Pape, E., van Oevelen, D., Moodley, L., Soetaert, K., Vanreusel, A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2013
• Subjects: Bacteria; Benthos; Deep sea; Stable isotopes; Nematoda [Nematodes]; ANE; Galicia Bank; MED; Mediterranean; Northeast Atlantic
• Online Access: http://imis.nioz.nl/imis.php?module=ref&refid=228733

Sediments sampled from the Galicia Bank seamount and the adjacent slope (northeast Atlantic), and from a western Mediterranean slope site, were injected onboard with 13 C-enriched dissolved organic matter (DOM) to evaluate nematode feeding strategies and the fate of DOM carbon in different benthic environments. We hypothesized that nematode 13 C label assimilation resulted from either direct DOM uptake or feeding on 13 C labeled bacteria. Slope sediments were injected with glucose (“simple” DOM) or “complex” diatom-derived DOM to investigate the influence of DOM composition on carbon assimilation. The time-series (1, 7 and 14 days) experiment at the seamount site was the first study to reveal a higher 13 C enrichment of nematodes than bacteria and sediments after 7 days. Although isotope dynamics indicated that both DOM and bacteria were plausible candidate food sources, the contribution to nematode secondary production and metabolic requirements (estimated from biomass-dependent respiration rates) was higher for bacteria than for DOM at all sites. The seamount nematode community showed higher carbon assimilation rates than the slope assemblages, which may reflect an adaptation to the food-poor environment. Our results suggested that the trophic importance of bacteria did not depend on the amount of labile sedimentary organic matter. Furthermore, there was a discrepancy between carbon assimilation rates observed in the experiments and the feeding type classification, based on buccal morphology. Sites with a similar feeding type composition (i.e. the northeast Atlantic sites) showed large differences in uptake, whilst the nematode assemblages at the two slope sites, which had a differing trophic structure, took up similar amounts of the DOM associated carbon. Our results did not indicate substantial differences in carbon processing related to the complexity of the DOM substrate. The quantity of processed carbon (5–42% of added DOM) was determined by the bacteria, and was primarily respired. The bulk of the added 13 C-DOM was not ingested by the benthic biota under study, and a considerable fraction was possibly adsorbed onto the sediment grains.