Braeckman, U.

Taheri, M.

Vanaverbeke, J.

Vincx, M.

Open Marine Archive

Short-term hypoxia does not affect nematode densities and vertical 
distribution patterns at the Belgian Part of the North Sea 
Taheri Mehrshad1,2, Ulrike Braeckman1, Magda Vincx1 and Jan Vanaverbeke1 
1 Marine Biology Research Group, Biology Department, Ghent University, Krijgslaan 281, S8,  
B-9000 Ghent, Belgium 
E-mail:  mehrshad.taheri@ugent.be  
2 Iranian National Institute for Oceanography, Tehran, Iran 
 
We investigated the effect of coastal hypoxia on nematode communities from different sediment 
types at the Belgian Part of the North Sea (BPNS). Different sediment types are characterised by 
different biogeochemical environments, which is reflected in nematode densities, community 
composition and vertical distribution in the sediment. As such, we investigated whether the effect of 
hypoxia depends on the identity of the receiving nematode communities. Samples were collected at 
St700 (median grain size: 25μm), St115 bis (median grain size 185μm) and St330 (median grain 
size 330-360μm), covering a wide gradient of biogeochemical environments. The environmental 
differences were reflected in significantly higher nematode densities at St115bis. PERMANOVA 
analysis (relative abundances) did not indicate a significant difference in the vertical distribution 
pattern in the field situation. 
 
In the lab, oxygen concentrations in the water column were manipulated to reach hypoxic 
conditions in the water columns (1.34±0.09 mg-1) or to maintain oxic condition (7.70±0.09mg-1). 
Samples were collected after 1 day (short term effect) and 7 days. Hypoxia in the water column 
resulted in reduced oxygen penetration depth in hypoxic treatments from Day 1 onwards at St330, 
and at Day 7 at both other stations. However, as oxygen penetration depth was limited to the upper 
cm at the onset of the experiment, direct oxygen-related hypoxia effects are limited to the upper 
cm of the sediment. 
 
Nematode densities and vertical distribution were not significantly affected by the experimental 
conditions at the start of the experiment. Hypoxia did not affect nematode total densities after 1 
and 7 days at any of the stations. Similarly, hypoxia did not affect the vertical distribution of the 
nematodes at any of the stations.  
 
Our results indicate that nematode communities from different sediment types from the BPNS were 
not negatively affected by short-term hypoxia, in terms of total densities and vertical distribution 
patterns. This can partly be explained by the buffering capacity of all types of sediment, as reflected 
in the relatively small differences in oxygen penetration depth in most of the sediments. On the 
other hand, nematode communities present at the start of the experiment probably were adapted to 
life in oxygen-stressed environments, as they were sampled after the deposition of the spring 
phytoplankton bloom. However, more detailed (but ongoing) analyses of the nematode communities 
(e.g. at species level) and environmental variables are needed to increase our understanding of the 
response of different nematode communities to short-term hypoxic events. 
 
 
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Short-term hypoxia does not affect nematode densities and vertical distribution patterns at the Belgian Part of the North Sea

Short-term hypoxia does not affect nematode densities and vertical
distribution patterns at the Belgian Part of the North Sea.
Introduction:
Hypoxia as a harmful phenomenon has recently increased in the marine coastal environment. For free living marine nematodes, the most dominant groups of
meiofauna, oxic condition is favourable and they can tolerant short-term anoxia but the activity level of them could be reduced by oxygen limitations. Also,
hypoxia can change nematode community structure and reduce diversity and abundance of some dominant nematodes. Different sediment types are characterised
by different biogeochemical environments, which is reflected in nematode densities, community composition and vertical distribution in the sediment. The aim of
present study was investigation the effect of short-term hypoxia on nematode densities and vertical distribution patterns in three different sediment types.
Mehrshad Taheri 1, 2, Ulrike Braeckman1, Magda Vincx1 and Jan Vanaverbeke 1
1. Ghent University, Biology Department, Marine Biology Research Group, Krijgslaan 281, S8, 9000;Ghent, Belgium. E-mail: mehrshad.taheri@ugent.be
2. Iranian National Institute for Oceanography. Tehran. Iran.
Materials and Methodes:
Sampling at three different stations  in June 2011 at the Belgian Part of the North Sea (BPNS).
•Station 700 (median grain size: 25 µm)
•Station 115 bis (median grain size 185 µm)
•Station 330 (median grain size 330-360 µm)
Field control: 18 cores, 9 for community structure and 9 for sediment condition
Experiment: 18 cores, 9 for community structure and 9 for sediment condition for each treatments.
Hypoxic condition (1.34±0.09 mg-1): day 1 and day 7 (with gas mixture containing 97% nitrogen).
Oxic condition (7.70±0.09 mg-1): day 1 and day 7 (with air pump)
In each treatment all cores were sliced into one centimetre interval till six centimetres.
Conclusion:
Our results indicate that nematode communities from different sediment types from the BPNS were not negatively affected by short-term hypoxia, in terms of
total densities and vertical distribution patterns. This can partly be explained by the buffering capacity of all types of sediment, as reflected in the relatively
small differences in oxygen penetration depth in most of the sediments. On the other hand, nematode communities present at the start of the experiment
probably were adapted to life in oxygen-stressed environments, as they were sampled after the deposition of the spring phytoplankton bloom. However, more
detailed (but ongoing) analyses of the nematode communities (e.g. at species level) and environmental variables are needed to increase our understanding of the
response of different nematode communities to short-term hypoxic events.
Results: 
Field  control:
• Total density, 115 bis > 330 = 700
• No significant differences in the vertical distribution pattern (relative abundance).
• Not significant differences between total densities of FC and Oxic day 1 in all stations.
Experiment:
• Reduced oxygen penetration depth in hypoxic treatments from Day 1 onwards at St330, and at Day7 at both other stations.
• No significant differences in total densities in Oxic day 1, Oxic day 7, Hypoxic day 1 and Hypoxic day 7 in all stations. 
• Hypoxia did not affect nematode total densities after 1 and 7 days at any of the stations.
• Hypoxia did not affect the vertical distribution of the nematodes at any of the stations.
-8
-6
-4
-2
0
Hy 1 Hy 7 Ox 1 Ox 7
D
ep
th
 i
n
 m
m
station 115 bis
-8
-6
-4
-2
0
Hy 1 Hy 7 Ox 1 Ox 7
D
ep
th
 i
n
 m
m
station 330
-8
-6
-4
-2
0
Hy 1 Hy 7 Ox 1 Ox 7
D
ep
th
 i
n
 m
m
station 700
-1000
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Ox1 Hy 1 Ox 7 Hy 7 Ox1 Hy 1 Ox 7 Hy 7 Ox1 Hy 1 Ox 7 Hy 7
115bis 330 700
D
en
si
ty
 (
In
d
/1
0
 c
m
2
)
0 1000 2000 3000
0-1 cm
1-2 cm
2-3 cm
3-4 cm
4-5 cm
5-6 cm
F C 115 bis
0 1000 2000
115 bis Oxic 1
0 1000 2000
115 bis Hypoxic 1
0 2000 4000
115 bis Oxic 7
0 2000 4000
115 bis Hypoxic 7
0 100 200 300
0-1 cm
1-2 cm
2-3 cm
3-4 cm
4-5 cm
5-6 cm
FC 330
0 200 400
330 Oxic 1
0 50 100
330 Hypoxic 1
0 200 400
330 Oxic 7
0 50 100
330 Hypoxic 7
0 100 200 300
0-1 cm
1-2 cm
2-3 cm
3-4 cm
4-5 cm
5-6 cm
FC 700
0 100 200
700 Oxic 1
0 100 200
700 Hypoxic 1
0 200 400
700 Oxic 7
0 200 400
700 Hypoxic 7
No significant differences in total density between day 1 and day 7 in both treatments. 
Vertical distribution of nematodes density (Ind/10 cm2) in all stations and both treatments.


Short-term hypoxia does not affect nematode densities and vertical distribution patterns at the Belgian Part of the North Sea

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