Benthic Protozoa and Metazoa living in deep anoxic and hydrogen sulfide conditions of the Black Sea: Direct observations of actively moving Ciliophora and Nematoda

Abstract

This study was conducted to search for living fauna in seafloor sediments from nearly 300 m water depth in the outflow area of the Bosporus into the Black Sea. During our investigations we identified seven higher level meiobenthic taxa in the anoxic and sulfidic sediments at 296 m water depth: Gromiida, Ciliophora, Foraminifera (soft-shelled), Nematoda, Kinorhyncha, Harpacticoida and one taxonomically unknown form. Hence, these Black Sea sediments seem to be a natural habitat for some eukaryotes. Furthermore, direct microscopic observations of alive and actively moving fauna demonstrates the presence of two species of ciliates, one species of free-living nematodes, and one unknown organism. As evidence, the activity of these organisms was recorded with a video camera. This indicates that metazoa and protozoa can live in the Black Sea under these more extreme conditions. However, the environmental factors and the specific physiological and biochemical processes used by the benthic fauna to retain metabolic activity and facilitate survival under anoxic and sulfidic conditions are still unknown. As well the distribution of benthos as a whole and of the individual taxa in other sulfidic sediments of the Black Sea needs to be investigated. Nevertheless, the presented observation of alive benthic organisms opens new perspectives to study of metazoan and protozoan life in Black Sea sediments lacking oxygen and containing sulfide.