Vertical Distribution of Benthic Macrofauna in Intertidal Habitats Frequented by Shorebirds at Merja Zerga Lagoon

The distribution of shorebirds is strongly linked to the availability of their prey consisting mainly of benthic invertebrates, especially during wintering and migratory stopovers. To better understand the functioning of this trophic link benthos-shorebirds at intertidal mudflats, it is necessary to evaluate the vertical distribution and importance of the fraction of benthic macrofauna accessible to shorebirds at these habitats. Nineteen stations were sampled in the main mudflats frequented by birds. Samples were cut into three slices of 0-5cm, 5-15cm and >15cm. The results showed a vertical stratification of the benthic macrofauna negatively correlated with the depth of the Merja Zerga lagoon intertidal sediments. The specific richness, density and biomass were concentrated at the surface layer of the sediments and shrink as we go more in depth. The polychaetes showed the most diverse distribution pattern along the three sedimentary layers. While the Bivalves dominated in term of biomass, the Gastropods dominated with regard to density. We observed also that the upper layer is mainly colonized by small species and / or individuals with high density and low biomass; this phenomenon is gradually reversed as we go more in depth. The sedimentary parameters (organic matter content and granulometry of the substrate) were not responsible for the variations observed in the distribution of the macrofauna along the sedimentary profile, as the vertical distribution of these factors was homogeneous to a depth of 20cm.