Problem definition: Overall it seems that meiofaunal taxa are more resistant to hypoxia than macrofauna and megafauna. Under natural conditions, severe oxygen depletion may be one major cause of elimination of macrofauna taxa, but whether that will negatively impact the meiofauna, by inducing more reduced redox conditions of the sediment, or have a positive effect due to decreased predation remains an open question. In view of the role of meiofauna as potential indicators of such events, it is of paramount importance to better understand the interaction between macrofauna, oxygen availability and their effect on the meiofauna communities. Objectives: In this project we are examining role of the food, oxygen conditions and macrofauna as structuring agents for meiofauna biodiversity patterns. This will increase the value of meiofauna as potential indicators of particular environmental conditions. We will manipulate sediments experimentally, varying (1) oxygen concentrations of the overlying water, (2) sediment organic loading and (3) activity of macrofauna. Planning 2003: Field sampling in the Westerschelde Estuary and continuation of laboratory experiments.