Vertical distribution and abundance of benthic invertebrates in profundal sediments of Mondsee,with special reference to oligochaetes

Two profundal sediment sites at the same depth (MO₁ and MO₇) in Lake Mondsee differed considerably in their trophic conditions. Based on organic carbon (weight loss on ignition) and redox values, MO₁ sediments could be classified as eutrophic, MO₇ sediment as oligo- to mesotrophic. Investigations on abundance, diversity and vertical distribution of meio- and macrofauna exhibited distinct differences between the two sampling sites. MO₇ showed a much higher diversity than MO₁. Seven species of ostracods and oligochaetes respectively, were found at MO₇, but only two species of oligocheates at MO₁. The vertical distribution of meiofauna at MO₇ corresponded to redox values. Chironomids were found in the uppermost 4 cm of sediments. Oligochaetes penetrated 15 to 20 cm into the sediment. Nearly 100% of the adult oligochaetes and cocoons occurred only below the first three centimeters of sediment. Their distribution patterns are discussed.