International Journal of Marine Science 2014, Vol.4, No.42, 1-11
7
Tardigrada, Tunicata and an unknown taxon. At the
same depths (117 m~296 m) filamentous fungi were
first discovered (Sergeeva and Kopytina, 2014). The
meiobenthos taxa made up the main proportion of the
fauna in the sediments (Figure 13). However,
distribution of benthos abundance was irregular along
observed stations at the same depth (252 m) (Figure
14).
Figure 12 Mean abundance (10
2*
ind*m
-2
)
of macrobenthos
found in cores (0~5 cm) sampled in the Bosporus outlet area of
the Black Sea
Figure 13 Distribution of bottom fauna (full core sample 0~5
cm) at Bosporus Strait outlet area of the Black Sea
Figure 14 Distribution of the benthic fauna from cores sampled
in different stations at 250 m water depth (0~5 cm)
6 Discussion
In general, metazoans are obligate aerobes. Certain
oligochaetes and nematodes, however, can live parts
of their life cycles under anoxic or even sulfidic
conditions (e.g. Fenchel and Findlay, 1995; Fenchel,
2012; Bernhard & Sen Gupta, 1999; Koho and
Pina-Ochoa, 2012). The same has been shown for
other multicellular organisms as well, which are
known to be able to live a part of the life cycle without
oxygen (Fenchel, 2012). Recently, Danovaro et al.
(2010) have demonstrated that also metazoan
(lociferans) can be adapted to the permanently anoxic,
highly saline and sulfidic conditions in the deep
Mediterranean L‟Atalante Basin. These meiofaunal
organisms are metabolically active and show specific
adaptations to survive these extreme conditions. As
well some nematode species can inhabit sulfidic
environments (Nuß, 1984; Wetzel et al., 2001). The
findings of anaerobic multicellular animals in the
sediment below the anoxic brine in the depths of the
Mediterranean Sea may be not too surprising, as in
general, when one searches in unusual environments,
one finds unusual organisms (Oren, 2012).
During our study we found traces of bioturbation in
hydrogen sulfide containing sediments. This was most
likely caused by the high densities and active
movements
of
macrobenthic
oligochaetes
(
Tubificoides
sp.), polychaetes (
Aricidea
sp. and
Capilellidae
g. sp.), large nematodes (
Theristus
sp.)
and other fauna we observed to live in the sediment.
This is despite the presence of sulfide in the sediment.
Sulfide is generally toxic for most organisms, but
some species have developed strategies for
detoxification (Nuß, 1984). For example, species of
the genus
Tubificoides
are able to tolerate hypoxia and
sulfidic
conditions
by
symbiosis
with
chemoautotrophic bacteria (Dubilier, 1994).
The overall abundance of benthic fauna from
sediments collected in the Bosporus outflow area of
the Black Sea suggest that the oxic/anoxic transition
zone supports a rich protozoan and metazoan
community with high abundances of especially
meiobenthos taxa. It is well known that all metazoans
have to be in contact with oxygen at least during part
of their lifetime (Fenchel, 2012) as they require
oxygen for synthetic pathways producing sterols,
collagen, and quinone tanning (Barrett, 1991). Our
data show presence of fauna also in samples obtained
from areas with anoxic bottom water. The high
nematodes and harpacticoides densities detected in
0
100
200
300
400
500
N (10
2
indiv. *m
-2
)
100
150
200
250
300
Depth, m
100
150
200
250
300
macro
meio
total
0
200
400
600
800
1000
1200
1400
1600
N (10
3
indiv.*m
-2
)
Depth, m
203
204
263
Mean
macro
meio
total
0
200
400
600
800
1000
1200
1400
1600
Station, N
N (10
3
indiv.*m
-2
)
