Abundance and characteristics of microplastics in commercially important bottom dwelling finfishes and shellfish of the Vembanad Lake, India.

This paper characterize microplastics (MPs) in the heavily urbanized, brackish water Vembanad Lake (India), focussing on some commercially important bottom-feeding fishes and shellfish (Arius maculatus, Etroplus suratensis, E. maculatus and Villorita sp.). The average abundance of MPs was higher in the water column (872 ± 573 nos./m3) than in finfishes (15 ± 13 particles per fish) and shellfish (23 ± 20 nos./ind.). Fibre was the most abundant MP type in the water and the organisms examined. The size of MPs obtained from finfishes ranged between 0.04 and 4.73 mm (4 ± 3 mm), with a majority of particles being <4 mm. No correlation was found between biological features (e.g. gut length, mouth size) of fishes and the size of MPs in their gut. In Villorita sp., the abundance of MPs was positively correlated with the size of the individuals. Raman spectroscopy confirmed the presence of chlorinated polyvinyl chloride, polyethylene, polypropylene and polyester in the samples.

Response of macrozoobenthic communities to summer monsoon upwelling and related hypoxia in the south eastern Arabian Sea shelf.

Coastal upwelling in the south eastern Arabian Sea (SEAS) leads to oxygen depletion over the continental shelf during the summer monsoon season (June-September), with latitudinal gradients in intensity. Based on two surveys in the onset (June) and peak (August) phases of the summer monsoon, the present study evaluates the response of macrozoobenthic communities (size >500 µm) to upwelling and consequent hypoxia (dissolved oxygen <0.2 ml/l) in the central sector of the SEAS shelf (10-12°N, 30-200 m). From the onset to the peak monsoon, macrozoobenthic density increased five-fold in the mid-shelf (50 m water depth), and nearly doubled in the outer shelf (100 m water depth) and shelf edge (200 m water depth). This was found to be a direct consequence of recruitment and proliferation of opportunistic polychaetes, particularly the spionid Paraprionospio pinnata, which was the single dominant species (52-78%) at all depths during the peak monsoon. With the establishment of the monsoon, the shelf communities (particularly 50-100 m depth sites) are thus transformed from relatively diverse assemblages to dense, single-species dominated ones. The shelf-edge communities (150-200 m depths), which are impacted with the perennial Arabian Sea oxygen minimum zone, and therefore harbour opportunist-dominated communities year-round. It is postulated that larvae of hypoxia-tolerant taxa are transported from the shelf edge by the process of upwelling onto the shelf. The settlement and survival of these larvae are regulated by the nature of shelf sediments and by the prevailing hypoxia. Thus, substantial recruitment of opportunists occurred in the outer and mid-shelf (50-100 m), but not in the inner shelf (30 m), where sedimentation from river discharge hindered settlement and survival of juveniles.