Nutritional importance of benthic bacteria for deep‐sea nematodes from the Arctic ice margin: Results of an isotope tracer experiment

Abstract

A stable isotope ( 13 C)-labeling experiment was performed to quantify the importance of bacterial carbon as a food source for an Arctic deep-sea nematode community. Bacterial functional groups were isotopically enriched with 13 C-glucose, 13 C-acetate, 13 C-bicarbonate, and 13 C-amino acids injected into sediments collected from 1280 m depth at 79uN, 6uE, west of Svalbard. Incorporation of the 13 C label into bacterial phospholipid-derived fatty acids (PLFAs) and nematodes in the top 5 cm of the sediment was monitored over a 7-d period. The 13 C dynamics of nematodes was fitted with a simple isotope turnover model to derive the importance of the different bacterial functional groups as carbon sources for the nematodes. The different substrates clearly labeled different bacterial groups as evidenced by differential labeling of the PLFA patterns. The deep-sea nematode community incorporated a very limited amount of the label, and the isotope turnover model showed that the dynamics of the isotope transfer could not be attributed to bacterivory. The low enrichment of nematodes suggests a limited passive uptake of injected 13 C-labeled substrates. The lack of accumulation suggests that the injected 13 C-labeled dissolved organic carbon compounds are not important as carbon sources for deep-sea nematodes. Since earlier studies with isotopically enriched algae also found limited uptake by nematodes, the food sources of deep-sea nematodes remain unclear.

Differing utilization of glucose and algal ­particulate organic matter by deep-sea benthic organisms of Sagami Bay, Japan

“…Many bacteria show higher growth rates with amino acids than with glucose and ammonium (Kirchman 1990). In some cases, acetate was a more preferable carbon source for bacteria relative to glucose and amino acids (Guilini et al 2010). Marine invertebrates prefer fatty acids or algal-derived amino acids to glucose (Baines et al 2005, de Goeij et al 2008.…”

“…the ingestion of 13 C-labeled microbes that had incorporated 13 C-glucose to build up their biomass. Guilini et al (2010) reported that Some benthic foraminiferal species are known to utilize bacterial carbon under experimental conditions (Lee et al 1966, Bernhard & Bowser 1992, Langezaal et al 2005. However, the contributions of bacterial carbon to the total carbon requirements of foraminifera are generally low based on direct evaluation in labeling experiments (Nomaki et al 2006, van Oevelen et al 2006b, Pascal et al 2008.…”

“…The concentration of DOC in sedimentary pore water is generally higher than that in the overlying seawater by values up to an order of magnitude, although most DOC is presumably refractory (Burdige 2002). This implies that some of the labile molecular components of the DOC could be possible carbon sources for deep-sea foraminiferal species.The uptake of DOC by a number of benthic taxonomic groups, including bacteria (Cahet et al 1990, Guilini et al 2010, benthic foraminifera (DeLaca et al 1981, DeLaca 1982, marine invertebrates (Shirayama 1992, Baines et al 2005, de Goeij et al 2008, Guilini et al 2010, and whole benthic communities (Sawyer & King 1993, van Oevelen et al 2006a has been reported. However, most previous studies were limited to shallow-water organisms that can utilize relatively large amounts of organic matter produced on the ocean surface.…”

Sink or link? The bacterial role in benthic carbon cycling in the Arabian Sea's oxygen minimum zone

“…Consistently, for deep-sea sediments Nomaki et al (2006) and Guilini et al (2010) found limited to no bacterivory by meiofaunal foraminifera and nematodes, previously thought to be major consumers of bacterial production. If faunal grazing does not constitute a main controlling factor of the bacterial community, then the latter must be controlled in a different way.…”

“…However, shorter experiments executed in similar settings did report significant tracer transfer to bacteria and fauna (Moodley et al, 2005a, b;Woulds et al, 2007;Guilini et al, 2010). Nevertheless, a 7 day period is relatively short if transfers from bacteria to metazoan's consumers involve multiple benthic compartments (e.g.…”