Problem definition: In the EU-funded project ECOFLAT (1996-1999) a large number of studies on the flows of materials and nutrients were conducted on the Molenplaat tidal flat in the Westerschelde. These studies demonstrated the importance of microphytobenthos and phytoplankton as the basis of most of the food chain in the intertidal flat. In contrast, detrital particulate organic matter appeared to be little processed by the micro-, meio- and macrofauna. In several species of macrofauna, there was also an ontogenetic shift in food preference. Several questions arise from these studies. is the macrofauna showing switching behaviour in its food preference and how flexible is it in selecting food? Is there an ontogenetic shift in food preference and what is the adaptive significance of this? Is meiofauna directly dependent on microphytobenthos, or rather on exudates and/or on microbenthic herbivores? Does the macrofauna influence microbial processing of the bulk organic matter, even if it does not use this matter as its own food? Objectives: To use stable isotopes ratios (both natural ratios and experimentally changed in deliberate tracer additions) to characterise the food of micro-, meio- and macrobenthos. To determine stable isotope ratios in specific biomarkers of different groups, in order to trace fluxes through the intertidal benthic food web. Planning 2000: Seasonal survey of natural stable isotope ratios in different species and different size classes of macrobenthos. Determination of stable isotope ratios in micro- and meifauna in cooperation with the University of Gent. In situ labelling experiments following the fate of microphybenthos. Tracer addition experiments using pre-grown algae to study the fate of phytoplankton organic matter in intertidal food webs.
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