The trophic significance of bacterial carbon in a marine intertidal sediment: Results of an in situ stable isotope labeling study

Abstract

We report the results of an in situ tracer experiment in an intertidal sediment, where bacterial carbon was tagged with stable carbon-isotope label, after the injection of 13 C-glucose. The appearance of label in bacteria (based on label incorporation in bacteria-specific, phospholipid-derived fatty acids) and subsequent transfer to meiobenthos (group level) and macrobenthos (species level) was followed for 36 days. The label dynamics of benthic taxa were either fitted with a simple-isotope model or evaluated against enrichment in bacteria, to derive the importance of bacterially derived carbon for the meiobenthos and macrobenthos. Although selective uptake of bacteria was evident, as 2.4 times more bacterial carbon was grazed as expected from indiscriminate feeding, bacterial carbon accounted on average for only 0.08 and 0.11 of the carbon requirements of meiobenthic and macrobenthic taxa, respectively. Additionally, the contribution of bacterial carbon to total carbon requirements did not depend on the living/feeding depth in the sediment or organism size (evaluated over a size range of four orders of magnitude). The observed overall low contribution of bacterial carbon implies that most intertidal benthic fauna depend primarily on other carbon resources that may assert a stronger control on the structure of intertidal-sediment communities.

Fate of peptidoglycan in an intertidal sediment: An in situ 13C‐labeling study

“…In addition to bacteria, fauna were an important pool of OC. Benthic macrofaunal biomass (dominated by the bivalve Macoma balthica and the polychaetes Heteromastus filiformis and Pygospio elegans) in the upper 10 cm was 1,624 mmol C m 22 (13 mmol C g -1 dry sediment), whereas meiofaunal biomass (dominated by nematodes and foraminifera) was smaller at 188 mmol C m 22 (1.5 mmol C g 21 dry sediment) (see Van Oevelen et al 2006). …”

“…In addition, a separate paper was dedicated to detailed analysis of the transfer of 13 C from bacteria to fauna via grazing (Van Oevelen et al in press). Van Oevelen et al (2006) documents strong loss of bacterial 13 C from the sediment during the 4.5-month sampling period.…”

“…The main data concerning total 13 C and total bacterial 13 C for the whole upper 10-cm layer of both sediment plots are presented in a companion paper (Van Oevelen et al 2006) that focuses at modeling the 13 C results to quantify loss processes for 13 C from bacterial biomass and the sediment. In addition, a separate paper was dedicated to detailed analysis of the transfer of 13 C from bacteria to fauna via grazing (Van Oevelen et al in press).…”

“…Experimental setup-The material presented in this paper is part of a larger 13 C-labeling study (Van Oevelen et al 2006). In May 2003, two 0.25-m 2 sediment plots were selected at a silty part of the Molenplaat intertidal mudflat in the turbid, nutrient-rich, and heterotrophic Scheldt estuary (The Netherlands).…”

“…Cores were sliced into three layers (0-2 cm, 2-5 cm, and 5-10 cm) that were analyzed for total C and 13 C in the bulk sediment, pore-water dissolved inorganic carbon (DIC), PLFAs, and benthic fauna. Further details on the experimental setup and analytical procedures can be found in Van Oevelen et al (2006). In addition to these analyses, a selection of sediment samples from the 0-2-cm layer of plot 2 and the 2-5-cm layer of plots 1 and 2 were analyzed for 13 C in hydrolysable amino acids (HAAs), including bacterial biomarker D-Ala. Because this paper is largely based on the [ 13 C]HAA data, it only deals with the layers that were analyzed for 13 C in HAAs.…”