Summary of Abstract Submission

Abstract Submission No. IO50-06-0025PresentationPoster

ECOLOGY AND DISTRIBUTION OF ASTEROROTALIA SP. FROM THE WESTERN BAY OF BENGAL

Thejasino Suokhrie*1, Manasa M.1, S.M. Saalim1, R. Saraswat1, R. Nigam1

1 National Institute of Oceanography, Goa, India

ABSTRACT :

The variation in foraminiferal species abundance is a function of its adaptive response to changing environmental conditions. Asterorotalia sp., a benthic foraminifera has been reported from varied substrates with a preference for hyposaline conditions. The effect of various physico-chemical properties of seawater on its distribution and abundance is, however debated. In view of this, a total of 90 surface sediment samples from the riverine influx dominated north-western Bay of Bengal have been collected from water depths of 25 m to 3000 m, covering the entire shelf, slope and a part of the abyssal region. The samples were analyzed for benthic foraminiferal abundance and Asterorotalia sp. was found in 25 samples. The relative abundance of living as well as fossil Asterorotalia sp. ranges from totally absent to a maximum of 32%. The abundance of Asterorotalia sp. is comparatively high in the shallow shelf region (25-76 m), closer to the river mouths. Its abundance in samples off Ganga-Brahmaputra and Krishna-Godavari riverine systems, is relatively high as compared to those in front of Mahanadi and Pennar rivers. Additionally, the abundance of Asterorotalia sp. in this region is comparatively lower than that in front of Irrawaddy river. A comparison of its abundance with ambient physico-chemical parameters suggests that contrary to previous reports, dissolved oxygen followed by temperature and salinity controls its distribution. The abundance of Asterorotalia sp. also correlates well with the pH of the ambient seawater. Therefore, the spatial variation in Asterorotalia sp. abundance, is attributed to terrigenous and freshwater influx and resultant change in physico-chemical conditions. This study provides a better understanding of the ecology of Asterorotalia sp. The findings can be used to reconstruct paleo-monsoonal fluctuations from the east coast of India.