MEPS 136:289-301 (1996)  -  doi:10.3354/meps136289

The activity of the respiratory electron transport system (ETSA), measured in vitro in conditions of V_max (i.e. with saturation of electron donors and acceptors), represents the respiratory potential of all communities sampled. From analysis of surface sediments from various oceanic areas, ETSA has been found to be correlated with the biopolymer (protein, carbohydrate, lipid) content which may represent the most labile fraction of the sedimentary organic matter. ETSA results expressed at constant temperature (e.g. 20*C) can be considered as an estimator of biomass, especially of the microbial biomass which contributes, in most cases, the greatest part of the sediment respiratory potential. Original and literature data reveal discrepancies between laboratory and field experiments, so that results obtained with cultured species cannot be directly applied to natural environments. A compromise conversion factor [particulate organic carbon (POC) biomass (ug) = ETS (ul O₂ h^-1) x 14.3] is proposed by the author. At in situ temperature, ETSA may theoretically be converted to respiration (R), which is the actual rate of electron transfer. The R/ETSA ratio used for conversion depends strongly on the availability of food. This ratio decreases from coastal to deep areas but results show that the gradient (from 0.4 in shallow sediments to 0.05 in deep sea areas, on average) is not as steep as previously thought. Due to the lack of accuracy of the R/ETSA ratio, the use of ETSA to calculate sediment community oxygen consumption is not very promising and direct measurements of respiration are preferable. Finally, it is concluded that the most important application of the ETSA measurement in sediments is its use as an estimator of the total microbial biomass.

ETS activity in sediments