Trace Metal Concentrations in Zooplankton from the Eastern Arabian Sea and Western Bay of Bengal

Abstract

Trace metal contents in zooplankton samples were estimated as a part of the Marine Research–Living Resource program at 24 stations in the Bay of Bengal (November, 2002) and 29 stations in the Arabian Sea (September–October, 2003) during the Cruises 209 and 217 of the Fishery and Oceanographic Research Vessel Sagar Sampada. The average metal concentrations in the Bay of Bengal zooplankton (Fe, 14,073 µg g−1; Co, 24.2 µg g−1; Ni, 29.5 µg g−1; Cu, 46.2 µg g−1; Zn, 2000 µg g−1; Cd, 18.7 µg g−1; and Pb, 6.55 µg g−1) were found to be higher of comparable magnitudes than the Arabian Sea zooplankton (Fe, 1786 µg g−1; Co, 14.2 µg g−1; Ni, 18.6 µg g−1; Cu, 21.5 µg g−1; Zn, 374 µg g−1; Cd, 16.5 µg g−1; and Pb, 4.0 µg g−1). The spatial variability of metal contents in zooplankton from both basins indicates that it is markedly enriched in coastal samples than offshore samples. The metal enrichment in zooplankton from the coastal areas of the eastern Arabian Sea occurs due to a combined effect of upwelling, riverine, and anthropogenic sources, whereas the latter two are only dominating in the coastal Bay of Bengal zooplankton. A comparison of average trace metal concentrations in the zooplankton from the Arabian Sea and Bay of Bengal showed that the enrichment of Fe, Zn, Cd, Ni, Cu, and Pb in the Bay of Bengal zooplankton may be due to high bioaccumulation factor of these elements, whereas the slight Co enrichment may be due to the bioavailability of this metal in the seawater.