Macrobenthos community response to the seasonal hypoxia associated with coastal upwelling off Kochi, along the Southwest coast of India

Abstract

This study presents the seasonal macrobenthic assemblages in the nearshore environment off Kochi along the southwest coast of India, which is exposed to the freshwater influx, and coastal upwelling associated seasonal hypoxia during the Southwest Monsoon [(SWM) (June-September)]. Monthly observations were made from three locations in different depth zones [inshore (6 m), nearshore (13 m) and coastal (28 m)] along a cross-shore transect off Kochi for one year (2014-15). During the SWM, the study area underwent a significant lowering of salinity in the surface waters due to enhanced freshwater influx and a remarkable oxygen deficiency in the subsurface waters due to upwelling. The Pre-Monsoon [(PRM) (March-May)] macrobenthic community was dominated by gastropods, which transformed into a less diverse and hypoxia adapted opportunistic species of polychaetes (Paraprionospio pinnata and Cossura coasta) and foraminifers (Bolivina sp.) during the SWM. This study showed a seasonal decline of the sensitive fauna and the dominance of opportunistic species as the effect of hypoxia in the study area during the SWM