International Journal of Marine Science, 2017, Vol.7, No.7, 59-66
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insignificant relation suggesting that the oxygen does not control the distribution and abundance of metazoan
meiofauna in OMZ. Several investigations in the world OMZ areas have observed strong correlation between food
quality and abundance of meiofauna and absence of oxygen effect. Cook et al. (2000) have reported that DO has
no effect on the nematode community-rather food quality appears to be the major predictor in the OMZ areas in
the Arabian Sea. According to Neira et al. (2013) bottom water oxygen and sediment organic matter are two
factors that exhibit steepest gradient in OMZ areas. There is however, contrasting report which emphasized the
role of oxygen in structuring meiofauna communities (Neira et al., 2001). Similarly Muthambi et al. (2004) found
the impact of oxygen on nematode. The oxygen limitation might directly control meiofauna composition at higher
taxonomic levels within the OMZ, it is believed (Neira et al., 2001). Outside OMZ where oxygen is available, a
number of oxygen sensitive group of crustacea were recorded (St. 7, 8, 9) and this also improved the overall
diversity of higher taxa in the area outside OMZ. Similarly Ansari et al. (2011) high number of taxa in meiofauna
of south east continental shelf of India.
The metazoan community in the present study area is characterized by two set of fauna, one for the OMZ area and
the other for the non OMZ area. Whether due to sediment characters, bottom temperature, DO or food, changes in
the meiofaunal taxa was recorded. In the non OMZ area of 900 m and above the temperature and sediment organic
carbon remained low while the oxygen values were highest. The oxygenated water may be the influencing factor
for more crustaceans groups in non OMZ. This goes against the report of Cook et al. (2000) where food is said to
control nematode population in OMZ of Arabian Sea. There are report of behavioral changes and mortality in
more sensitive groups such as crustacean exposed to induced hypoxia and anoxia (Miller et al., 2002; Haselmair et
al., 2010). Such changes are expected in the OMZ area where very low numbers of crustaceans were recorded.
The distribution and abundance of meiofauna particularly in the OMZ area where sediment organic carbon
recorded highest value, support the hypothesis of Cook et al. (2000). Several investigations on world OMZ areas
have also observed strong correlation between food quality and abundance of meiofauna and absence of an
oxygen effect. It is suggested that total density of meiofauna in OMZ are never reduced, rather it recorded the
highest density within OMZ (Levin et al., 1991; Neira et al., 2001). These authors feel that biological interactions
between the larger organisms and predation by macrofauna might be more important. There is great deal of
variability in the total density of meiofauna recorded from different regions particularly in he OMZ areas. These
are correlated with enhanced sedimentation regimes of particular organic matter and food supply (Sommer and
Pfannkuche, 2000; Schwartz, 2007). Lambshead et al. (1994) found low nematode abundance in San Diego
Trough where oxygen concentrations were in the range of 15-60 μmol. In the present study we recorded low
percentage of nematode (< 45%) at those stations having oxygen in the range of 16 to 97 micromole. In areas of
permanent hypoxia specific stress responses are induced in metazoan meiofauna particularly the nematode to cope
up with situation. The
nematodes use high organic matter in sediment to multiply and flourish in the absence of
most predators in OMZ. They are the lone group recoded in maximum number from all stations. The secret of this
is that the nematodes are more tolerant to anoxia than other meiofaunal taxa (Giere, 1993). This was proved in the
vertical distribution also. The higher oxygen concentration appears to be responsible for increased number of
crustacean taxa which otherwise are sensitive to oxygen minima and eliminated under anoxic condition.
The meiofauna in all conditions and at all depths have shown consistent decline with increasing depth in sediment.
It may be consequences of changes in abiotic and biotic factors, triggered by biogeochemical processes under
highly stressed condition (Danovaro et al., 1995). The dominance of nematode particularly in the area of lower
OMZ suggests their ability to adapt and survive in hypoxic condition. Such adaptation and tolerance in nematodes
in the OMZ areas have been reported earlier (Levin et al., 2009). The relative proportion of each of the four
feeding types in a community depends on the nature of the available food which in turn is reflected by the nature
of the habitat (Platt and Warwick, 1980).
It appears that the hypoxic conditions puts additional pressure on more sensitive benthic groups and drive them
away. Abundant food and absence of predators and competitors provide a more favorable condition for the
nematodes to sustain. There are predictions of further decline in dissolved oxygen of the deep ocean due to global
