Influence of upwelling on distribution of chaetognath (zooplankton) in the oxygen deficient zone of the eastern Arabian Sea

The study addresses the coupled spatial scales in the physico-chemical variables and chaetognaths in the upwelling system of the eastern Arabian Sea during the 2005 summer monsoon. We studied the taxon between 0 and 1000 m depth along seven zonal sections between 8°N and 19°N and especially observed the vertical stratification of the animals. In the upwelling regions, higher chaetognath abundance was observed resulted by the local population growth and advection of the upwelling preferred epipelagic species. Abundance weight (Aw) value further helped to understand the mode of distribution of the chaetognath community around the upwelling locations. The variation in the depth-weighted average values of different species between the upwelling and non-upwelling sites helped to identify the dissimilarity in their coupling with the abiotic components. As this eastern boundary current region further draws research interest as one of the major natural oxygen deficient system in the global ocean, the role of this hypoxia was shelved separately from the influence of upwelling in the heterogeneity of distribution of chaetognaths. In our study, two mesopelagic species Eukrohnia fowleri and Eukrohnia minuta were identified as the indicator species of this upwelling process. Our observation suggests that the temporal physical event (upwelling) plays a decisive role in the heterogeneity of the spatial abundance, community composition and diversity of chaetognaths in this least studied eastern boundary current system.