MEPS 204:79-92 (2000)  -  doi:10.3354/meps204079

Stable isotopes as trophic tracers: combining field sampling and manipulative labelling of food resources for macrobenthos

Peter M. J. Herman1,*, Jack J. Middelburg1, John Widdows2, Cathy H. Lucas3, Carlo H. R. Heip1

1Netherlands Institute of Ecology, PO Box 140, 4400 AC Yerseke, The Netherlands
2Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, United Kingdom
3Southampton Oceanography Centre, European Way, Southampton SO14 3ZH, United Kingdom

ABSTRACT: We combined 3 different approaches to determine the relative importance of microphytobenthos production as food for intertidal macrobenthic animals: (1) the natural abundance of stable-isotope ratios of carbon and nitrogen, (2) an in situ deliberate tracer addition of 13C-bicarbonate, which was transferred through the benthic food chain after its incorporation by benthic algae, and (3) a dual labelling experiment in a flume, where pelagic and benthic algae were labelled with 15N and 13C, respectively. The results of the 3 approaches confirmed the high importance of microphytobenthos as a food source for (surface) deposit feeders. Despite the clearly demonstrated resuspension of benthic algae at high current velocities, suspension feeders appeared to depend almost exclusively on pelagic algae (and possibly detrital carbon) as a food source. Based on the results of the experiments, we determined an approximate degree of dependence on microphytobenthos for different species of intertidal macrobenthos. The macrobenthic biomass at 5 study locations, when weighted by these coefficients, correlated very well with measured productivity of the microphytobenthos.

KEY WORDS: Food web · Microphytobenthos · Deposit feeding · Suspension feeding · Westerschelde-flume

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