Spatial variability of copepod species distribution in the eastern Arabian Sea in pre-monsoon conditions

This work examines the spatial variability among mesozooplankton abundance and copepod species diversity along the continental margin prior to the onset of southwest monsoon in the eastern Arabian Sea during the year 2011. The eastern Arabian Sea experiences seasonal hypoxia during the receding phase of monsoon that corresponds to low copepod abundance in the slope region. Collectively, fifty copepod species were identified over the continental margin where the diversity index (H') ranged between 2.59 and 3.73. Bray-Curtis cluster analysis clustered the stations into three groups that corresponded to the continental shelf, slope and break reaches of the eastern Arabian Sea. This spatial variability among the groups is mainly ascribed to changes in the relative contributions of the prevailing species. The distinct genera of the continental shelf were Microsetella spp. and Temora turbinata; at the slope region, Oncaea spp. and at shelf-break, Pleuromamma indica. Overall, herbivorous copepods were numerically abundant at the continental shelf and carnivores at the slope. The discrepancy between the distributions of herbivorous versus carnivorous copepod assemblages may be attributed to environmental factors such as ambient water dissolved oxygen and phytoplankton biomass.