Nutrient Dynamics in European Water Systems
Synthesis Results

4. Effects of altered nutrient discharges on the functioning of coastal and estuarine food webs (3 of 3)

Tracer experiments show that benthic organisms primarily feed on fresh vegetal rather than detritus (Herman et al., 2000). The importance of microphytobenthos as a food source for macrofauna deposit feeders was clearly stressed in a study by Herman et al. (2000). Conversly, macrofauna filter-feeders were shown to strongly depend on phytoplankton food sources.

A field confirmation for the trophic link between deposit-feeding macrofauna and microphytobenthos was produced by Herman et al. (2000). First a degree of dependence on microphytobenthos is approximated for the macrofauna species isotope signature and used to weigh the corresponding biomass. Secondly, the macrofauna biomass at 5 study locations is plotted against the microphytobenthos production. The clear relation between the microphytobenthos production and macrofauna biomass (Figure 4.2(a)) illustrates the tight trophic link between both compartments as was suggested by their isotopic ratios.

Stable isotope techniques have shown here their ability to identify trophic pathways in benthos. Further progress and application of these techniques should greatly contribute to a better representation of the trophic fluxes between the benthic components.