International Journal of Marine Science 2014, Vol.4, No.42, 1-11
1
Research Report Open Access
Benthic Protozoa and Metazoa Living under Anoxic and Sulfide Conditions in the
Black Sea: Direct Observations of Actively Moving Ciliophora and Nematoda
Nelli G. Sergeeva
1
, Sofia A. Mazlumyan
1
, Anna Lichtschlag
2
, Moritz Holtappels
2
1. Institute of the Biology of the Southern Seas, Sevastopol, Crimea, Russia
2. Max Planck Institute for Marine Microbiology, Germany
Corresponding author email
International Journal of Marine Science, 2014, Vol.4, No.42 doi: 10.5376/ijms.2014.04.0042
Received: 04 Jun., 2014
Accepted: 02 Jul., 2014
Published: 07 Aug., 2014
Copyright
©
2014 Sergeeva et al., This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted
use, distribution, and reproduction in any medium, provided the original work is properly cited.
Preferred citation for this article:
Sergeeva et al., 2014, Benthic Protozoa and Metazoa Living under Anoxic and Sulfide Conditions in the Black Sea: Direct Observations of Actively Moving
Ciliophora and Nematoda, International Journal of Marine Science, Vol.4, No.42 1-11 (doi: 10.5376/ijms.2014.04.0042)
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 unknown animal. 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.
Keywords
Live eukaryotes; Deep-water; Anoxia; Abundance trends; Black Sea
Introduction
The Black Sea is a deep marginal meromictic sea and
one of the largest and best-studied permanently anoxic
water bodies in the world. With increasing water depth
dissolved oxygen concentrations decrease, oxygen
deficiency (hypoxia) and depletion (anoxia) occurs
and hydrogen sulfide starts to build up in the water
column below about 200 m. At these depths the Black
Sea is often referred to as an environment that is
populated only by microbes but remains azoic or
lifeless with regard to higher forms of life (Sorokin,
1962; Zhizhchenko, 1974, Kiseleva, 1979). One of the
most characteristic features of such euxinic
environments is probably the absence of macroscopic
benthic fauna. In the absence of bottom-dwelling
organisms, responsible for bioturbation and bioirrigation,
sediments can accumulate without vertical or horizontal
biological mixing (Treude, 2012).
The knowledge of presence of oxygen only in trace
amounts limited hydrobiological investigations of the
deeper parts of the Black Sea and eukaryotic life
under sulfidic conditions is still under debate. As
result, it is still argued if eukaryotic life in the sulfidic
and anoxic Black sea waters and sediments can exists
(Zaitsev et al., 2007, 2008). However, the first direct
evidence of living multicellular animals under anoxic
and sulfidic conditions was provided by the findings
of alive and metabolically active meiofauna in the
deep hypersaline L'Atalante basin (Mediterranean Sea)
at water depths of more than 3,000 m, where the
anoxic sediments were colonized by a natural
population of loriciferans that were able to reproduce
(Danovaro et al., 2010). Adaptations to this
permanently anoxic condition with sulfide
concentrations of up to 2.9 mmol/L imply that these
organisms have developed specific survival
mechanisms. Currently, it is unknown what type of
metabolism may drive the growth of Loricifera in this
inhospitable environment, however the presence of
hydrogenosome-like organelles and associated
