Unravelling the complex structure of a benthic community: A multiscale-multianalytical approach to an estuarine sandflat

We evaluated scale-dependent patterns of distribution of sandflat macroinfauna of a coastal lagoon, using different analytical approaches. The sampled area was divided into three sectors (outer, inner-north, inner-south) containing small promontories. At each side of the promontories we defined stations in a line transect across the sandflat. Thus, we evaluated sediment characteristics and macroinfaunal responses to sectors, orientations and intertidal levels; animal–sediment relationships were also studied. At a large scale, there was a clear pattern of sediment composition and macroinfaunal abundance. While the outer sector had medium to coarse sands, reflecting the high hydrodynamic conditions existing near the lagoon entrance, the inner sectors showed sandy and muddy sediments. Most species were in low abundances at the outer sector. At small scale, macroinfaunal abundance and species richness decreased sharply towards the upper sandflat level. Also at small scale, sediment composition limited the maximal densities reached by all species, with exception of the deposit-feeding polychaetes. Thus, the macroinfaunal community at muddy sediments was dominated by burrowing deposit-feeders, while all species peaked in sandy sediments. Our results suggest that physical factors shaping macroinfaunal communities operate at different scales and are better detected using several analytical approaches. Large scale patterns, associated with along-shore variations in disturbance by currents, were detected as changes in the mean abundance of macroinfauna. Small scale patterns, related to sediment characteristics, were observed as changes in maximal densities of macroinfauna. Small scale patterns, associated with the level of inundation of the sandflats, were detected through changes in the abundance and presence of macroinfauna. The evaluation of the role of the physical conditions on communities must involve the use of several sampling and analytical approaches.