T. Joseph

Bioaccumulation of Toxic Metals by Fish in a Semi-Enclosed Tropical Ecosystem

Concentrations of Zn, Cd, Pb, and Mn in different tissues of 17 species of fish from a tropical estuary (Cochin backwaters) are presented. The metal selectivity index (MSI) was found to be a better tool compared with the tissue selectivity index (TSI) for explaining bioaccumulation. Regardless of the tissue type, accumulation was maximum for Zn and minimum for Cd. A distinct metal accumulation capacity for each species was noteworthy. The low variability in metal content in the gills indicated its inertness towards bioaccumulation compared with muscle or liver. The high positive correlation between Zn and Pb in tissues is indicative of the anthropogenic impact in the estuary. Conclusions are that, in a weakly polluted area, the organ of choice for estimating bioaccumulation potential is the liver, whereas in a heavily polluted area, the tissue of choice is the gill. The data presented here may be of help for forensic investigations in tropical ecosystems, for evaluation of contaminant impact, and for assessing past contamination events. Fish are good indicators of contamination, and the composition of bioaccumulative data for different species can serve in establishing a bioaccumulation database for that area, useful as a starting point (background) in forensic investigations.

Trace metal concentrations in zooplankton from the eastern Arabian Sea and western Bay of Bengal

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.

Biogeochemical characteristics of the surface sediments along the western continental shelf of India

Surface sediments from the western continental shelf of India were analysed for total organic carbon (TOC), total nitrogen (TN), total hydrolysable carbohydrates (TCHO) and proteins (PRT) during the late summer monsoon (September–October, 2003) and pre-monsoon (March–April, 2004) seasons. The region experienced entirely different hydrographic characteristics and productivity patterns during the two seasons. Low oxygenated, cold, nutrient rich (DO<180 μM, SST<28°C, NO3>2 μM) surface waters and the existence of subsurface suboxia were the hydrographic features during late summer due to the persistence of upwelling. Meanwhile, during pre-monsoon the region was oligotrophic and oxygen saturated (DO>200 μ M, NO3<2 μ M). Satellite imagery, in situ Chl a and zooplankton biomass showed high production along the region during late summer compared to pre-monsoon. Sedimentary organic matter (SOM) was of marine origin during both seasons, as indicated by the C/N ratios. TCHO+PRT: TOC and PRT: TCHO revealed aged organic matter and did not change between the seasons. During late summer, TOC and the reactive organic matter (TCHO and PRT) in the surface sediments were concentrated along the regions (13–17° N) where active upwelling was observed, suggesting a close coupling between SOM characteristics and the surface ocean productivity.

Biogeochemistry of the surficial sediments of the western and eastern continental shelves of India

Abstract Even though continental margins cover only about 7–9% of the world ocean area, they are important sites for organic carbon accumulation and hence play a major role in biogeochemical carbon cycling. Surface sediments from the western and eastern continental shelves of India were studied for their total organic matter content and the labile constituents such as total carbohydrates and proteins to get a better understanding of the hydrological and biogeochemical differences of the two regions on the nature of organic matter reaching the surface sediments. The sampling along the west coast was done during September–October 2003, when upwelling signatures were found to be still persisting along the shelf as evidenced by the low-oxygenated, nutrient-rich surface waters. The eastern shelf was sampled during November–December 2002. The shelf was found to be oxygen saturated and oligotrophic during the season. The surface sediments of the west coast contained a greater quantity of total organic matter when compared to the east coast, but the percentages of labile constituents of total organic matter in the sediments were found to be higher in the east coast by a factor of three as compared to the west coast. The differences in the productivity patterns and the hydrographical conditions were found to exert a major influence on the quantity and composition of organic matter in the surface sediments of the western and eastern continental shelves of India.