The microplankton organisms at the oxic-anoxic interface in the pelagial of the Black Sea

Abstract

The semi-permanent anoxia in the deep-waters of the Black Sea supported the formation of a unique microplankton community at the oxicanoxic interface. One group of ciliates (Pleuronema marinum, Askenasia sp., species of the families Tracheliidae, Holophryidae and Amphileptidae) inhabited the water layer just above the upper boundary of H2S, and was spatially associated with and fed on large colorless sulphur bacteria (Thiovulum spp.). Other ciliates (species of order Scuticociliatida) populated the upper layer of the H2S zone. A significant part of them possessed ectosymbiotic bacteria. Since the metazoans were not found in the O2 and H2S boundary layer, the protist community is considered to be the main factor in utilization of chemotrophic bacterial production.