International Journal of Marine Science, 2017, Vol.7, No.7, 59-66
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margin and slope (beyond 1100 m) the values reduced significantly. This zone falls out side the OMZ area. The
calcium carbonate content of the sediment was in the range of 46.5 and 67.4%.
Table 1 Physico-chemical parameters of the study stations
# Station/depth
Temperature (°C)
Salinity(psu)
Dissolved Oxygen (µM) Organic Carbon (%) Calcium Carbonate (%)
1 (500 m)
12.4
35.18
1.3
4.30
53.8
2 (650 m)
11.84
35.20
0.5
-
-
3 (700 m)
10.59
35.14
1.0
-
-
4 (799 m)
10.36
35.12
1.2
5.66
49.7
5 (800 m)
9.86
35.09
3.0
3.11
67.4
6 (900 m)
9.24
35.02
6.2
2.18
-
7 (1100 m)
7.78
34.88
12.3
3.15
46.8
8 (H1100 m)
7.8
34.90
15.2
1.88
51.2
9 (1956 m)
3.24
34.66
97.2
0.78
46.5
2.2 Meiofauna
A total of fifteen taxonomic groups were recorded from the study area with different taxa showing different
relative dominance (Table 2). The most abundant and widely distributed taxa were nematode (30.7-91.5%),
harpacticoid copepods (4.2-31.5%), polychaeta (1.8-19.2%), turbellaria (0-4.0%), and foraminifera (0-4.0%),.
Other groups recorded in low number from few stations were gastrotricha, oligochaeta, amphipoda, ostracoda,
kinorhyncha, cladocera, cumacea, tanaidacea and tardigrada. Total meiofauna density is shown in Figure 2.
Maximum density (164/10 cm²) was recorded at St. 1 (500 m). The second highest density (87/10 cm
2
) was
observed at 799 m. This was followed by 83/10 cm
2
at 900 m depth and the least density (23/10 cm²) was
observed at 650 m. The highest and lowest densities were recorded in the OMZ area where the oxygen was 1.3
and 0.5 µm, respectively. The meiofauna was dominated by nematoda (8-152/10 cm
2
) and their contribution was
34-92% of total meiofauna. Nematode abundance was high (91.5%) in shallow region of the shelf, decreased to its
lowest value in the lower part of the OMZ and then increased towards the deeper region where the oxygen
concentration was high. The mean meiofaunal density in the OMZ area was 65/10 cm
2
while in non OMZ area it
was 52/10 cm
2
. There was however exception where the density was not depth specific. They were followed by
harpacticoida and polychaeta in the order of abundance. Greater diversity of meiofaunal taxonomic groups (10
taxa), was recorded at the deepest station (1956 m) with highest oxygen values while the least number of groups
were found at 700 m where the oxygen was only 1 micromole.
Table 2 Relative (%) dominance of meiofaunal taxa at the study stations
Taxa
#1 (500 m) #2 (650 m) #3 (700 m) #4 (799 m) #5 (800 m) #6 (900 m) #7 (1100 m) #8 (H1100 m) #9 (1956 m)
Nematoda
91.5
72
68.9
78.1
71.4
68.8
30.7
48.9
42.1
Harpacticoida
4.2
8.0
17.2
5.7
7.14
12.0
23.0
27.6
31.5
Polychaeta
1.8
8.0
10.3
11.4
7.14
9.6
19.2
8.5
10.5
Turbellaria
1.2
4.0
1.2
3.6
3.8
3.5
Foraminifera
1.2
4.0
3.4
2.4
Ostracoda
2.4
3.8
3.5
Amphipoda
7.6
2.12
Cumacea
1.75
Cladocera
3.8
1.75
Tanaidacea
1.75
Kinorhyncha
1.2
3.4
2.4
Bivalvia
4.0
7.14
7.6
2.12
1.75
Tardigrada
1.75
Gastrotricha
2.12
Oligochaeta
7.14
4.25
