On the vertical distribution of the microfauna in the sediments of a brackish-water beach

Abstract

The vertical distribution of the microfauna in the sediments of the water-covered parts of a beach on the island of Askö (Baltic Sea) was investigated by quantitative methods. Factors such as temperature, salinity, grain size, oxygen, pH and redox potential were measured at various depths in the sediment. The members of the microfauna, especially the ciliates, showed a characteristic vertical zonation. The vertical extension of the species could be correlated with the redox potential of the sediment, especially the depth of the redox-discontinuity layer. The possible reasons for this are discussed, the most important probably being the type of bacterial flora characteristic of different electrode potentials. A quantitative estimate on the different taxonomic groups of the microfauna in the investigated area is given. Ciliates were most numerous (100–480 specimens per ems) while the most important metazoan groups (turbellarians, nematodes, rotatorians, oligochaetes and harpacticoids) each were represented by 10 to 500 times fewer individuals.