Abstract
A quantitative study of metazoan meiofauna across the oxygen minimum zone (OMZ) of continental margin in the N-E Arabian Sea in the depth range 500-1965 m was carried out in September-November 2008. Bottom water oxygen and sediment organic carbon showed large variation between stations. The bottom water temperature and salinity was very similar in the area. The fauna was dominated by nematoda followed by harpacticoid copepoda and polychaeta. Maximum meiofaunal density of 164/10 cm 2 was recorded at St. 1 (500 m) and the lowest density of 25/10 cm² was observed at St. 2 (650 m) which coincided with lowest oxygen concentration. Total abundance of meiofauna was significantly lower than those reported from other areas. The average density was high (65/10 cm 2 ) in OMZ than in non OMZ (52/10 cm 2 ) area. Nematodes were the dominant taxon at every station. The dominance was particularly significant at those stations having very low oxygen. The meiofaunal density was positively correlated with sediment organic carbon while oxygen exhibited a negative correlation. Epibenthic Crustacean groups were more in areas of non OMZ having high oxygen. Vertical distribution revealed consistent reduction in total density and major taxa with increasing depth in sediment. Maximum density was recorded in top 0-2 cm layer. Among environmental parameters the availability of food in the form of sediment carbon appeared to be key factor in controlling meiofauna in study areas.
Highlights
Our understanding of the biological oceanography of the deep Arabian Sea has come largely through systematic collection of data during different oceanographic cruises (Qasim 1982; Angel, 1984)
2.1 Physico-chemical parameters The area of investigation is located in the north east Arabian Sea across the continental margin (Figure 1)
The lowest dissolved oxygen was measured at a depth of 650 m in the upper oxygen minimum zone (OMZ) station and the highest was at a depth of 1956 m out side OMZ
Summary
Our understanding of the biological oceanography of the deep Arabian Sea has come largely through systematic collection of data during different oceanographic cruises (Qasim 1982; Angel, 1984). Limited sources of water replacement and high microbial activity in north eastern Arabian Sea have produced an intense and unusually deep oxygen minimum layer. It has supported one of the largest well defined OMZ where about 285000 km of continental margin in the depth zone100-1500 m seafloor is impacted (Helly and Levin, 2004; Stramma et al, 2008). To date there are limited studies on marcofauna and meiofauna community distribution on the continental margin including the OMZ of the Arabian Sea (Cook et al, 2000; Ingole et al, 2010; Jaleel, 2012). The nematodes among meiofauna tend to be more tolerant than macrofauna to anoxia (Levin et al, 1991)
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