Abstract. The paper deals with the standing stock of macrobenthic infauna and associated environmental factors influencing the benthic community in the shelf region of the northwest Indian coast. The data were collected onboard FORV Sagar Sampada during the winter monsoon (January-February, 2003) to understand the community structure and the factors influencing the benthic distribution. The environmental parameters, sediment characteristics and macrobenthic infauna were collected at 26 stations distributed in the depths between 30 and 200 m extending from Mormugao to Porbander. Total benthic abundance was high in lower depths (50-75m), and low values noticed at 30 m depth contour was peculiar. Polychaetes were the dominant group and were more abundant in shallow and middle depths with moderate organic matter, clay and relatively high dissolved oxygen. On the other hand crustaceans and molluscs were more abundant in deeper areas having sandy sediment and low temperature. High richness and diversity of whole benthic groups observed in deeper depths counter balanced the opposite trend shown by polychaete species. Generally benthos preferred medium grain sized texture with low organic matter and high organic matter had an adverse effect especially on filter feeders. Deposit feeding polychaetes dominated in shallow depths while carnivore species in the middle depths.Ecologically, benthos were controlled by a combination of factors such as temperature, salinity, dissolved oxygen, sand and organic matter and no single factor could be considered as an ecological master factor.

In the central and southern North Sea, and in the Dutch coastal zone, total cadmium (Cd) concentrations in water are 0.02 ± 0.01 µg/L and 0.06 ± 0.02 µg/L, respectively. Cadmium in the estuarine waters of the Dutch Wadden Sea varied from 0.03 ± 0.01 µg/L in the western part to 0.08 ± 0.03 µg/L in the eastern part (van Zeijl et al. 1994). In whole sediment, the Cd background concentration for the Wadden Sea is 0.5 ± 0.01 µg/g dry weight (dw), whereas the reference concentration is 0.08 ± 0.02 µg/g dw (Anon 1994). The concentrations of total-Cd in surface bulk sediments (0-2 cm) of the central North Sea (Oyster Grounds), and of intertidal mud-flats in the western Wadden Sea varied from 0.05 to 0.15 µg/g dw and from 0.13 to 0.46 µg/g dw, respectively (calculated from Kahn et al. 1992). These concentration ranges match the reference Cd concentration for Wadden Sea whole sediment (0.5 ± 0.01 µg/g dw; Anon 1994). Cadmium concentrations in surface sediments of the Dutch coastal zone and estuaries are only slightly elevated compared to the 0.2 µg/g dw, considered as the background concentration in pristine areas, but well below the level of 10 µg/g dw at heavily contaminated sites (Bryan and Langston 1992).The relationship between cadmium levels in sediments and the biota is uncertain and contradictory. Bryan and Hummerstone (1973) described already 2 decades ago a linear relationship between cadmium concentrations in the polychaete worm Nereis diversicolor and in surface sediments. However, in the closely related polychaete Nereis virens, cadmium is absorbed from the interstitial water rather than from sediment particles (Ray et al. 1980). Also, more recent data indicate that uptake from sediment fractions either does not occur or the availability of sediment-bound metals to benthic biota is very restricted (Samant et al. 1990;Bryan and Langston 1992). In general, macrobenthic organisms accumulate cadmium from the water by absorption and diffusion across the body surface and by ingestion of food and particulates. Cadmium concentrations in blood, intestine and body-wall of the polychaete worm Arenicola marina from the field varied from 5-25 ng/mL, 0.2-3.6 µg/g dw, and 0.5-1.5 µg/g dw, respectively (Everaarts unpublished data).The present experimental laboratory study reports on the distribution of cadmium in the sediment column, and the uptake in the blood/coelomic fluid, intestine and body-wall of lugworms at low cadmium concentration exposure. The aim of the study was to determine possible interaction between the vertical distribution of sediment-bound cadmium and the bioturbating activity of lugworms.