Asokkumar Bhattacharya

Spatiotemporal variation in benthic polychaetes (Annelida) and relationships with environmental variables in a tropical estuary

Annelida constitute a dominant functional component in soft-bottom macrobenthic communities and reveal a wide range of adaptability to different marine and coastal habitats. Analyses in different polychaete assemblages and their responses to habitat conditions reflect the biological effects of marine pollution and habitat disturbance. The present study is designed to study colonization and community structure of polychaetes in two ecologically distinct locations of the Sundarban Biosphere Reserve on the northeast coast of India. Polychaete assemblages are characteristically different at the two sites in the extreme northern (Ghusighata) and southern (Gangasagar) portions of the Biosphere Reserve. Levels of heavy metals in polychaete body tissues also reveal interspecific and regional variations. The predominant polychaete fauna exhibited a distinct and unique assemblage of two types: (i) Mastobranchus indicus – Dendronereides heteropoda in the sewage-fed substratum at Ghusighata and (ii) Lumbrinereis notocirrata – Ganganereis sootai – Glycera tesselata at Gangasagar at the mouth of the Hugli estuary where chronic anthropogenic stress and contamination with agricultural and industrial effluents occur. The faunistic composition of polychaetes and their potential for the accumulation of heavy metals from the ambient medium are distinctly different. The study demonstrates that textural composition of the sediments, together with hydrodynamic and geotechnical properties, seem to have the greatest control to quantify the differences of the polychaete community in the two study stations. An in-depth comparative study of polychaete community structure at multiple spatial scales is strongly recommended for future environmental impact assessment in this fragile environment.

Impact of Overexploitation of Shellfish: Northeastern Coast of India

Abstract India has a very extensive coastline of about 7515 km, rich in diverse living resources. These resources continue to deteriorate with rampant harvesting or are altered for other uses such as aquaculture and fisheries. The present paper deals with degrading coastal habitats in northeastern India, and projects the intensity of the stress arising from the collection of tiger prawn seeds (Penaeus monodon) for aquacultural farms and molluskan shells for poultry feed and edible lime. Indiscriminate exploitation of these resources leads to a heavy reduction of the species concerned and other associated marine communities. The magnitude of such destruction has been quantified. The impacts of biodiversity loss and their after-effects on the ecobalance of this coastal system have become a matter of great concern to ecologists to maintain security and sustainability. The authors propose a public awareness program on themes relating to the importance of biodiversity for human livelihoods.

Backwash-and-swash-oriented current crescents: indicators of beach slope, current direction and environment

Abstract Backwash-and-swash-oriented current crescents, which are confined to the swash zone of beach environments, are reported, with their detailed morphology and formation mechanism, from the siliciclastic fine sandy beaches of Sagar Island and Lower Long Sand, two tidal islands of the Ganga estuary, northeast India. Morphologically, the swash-oriented arms of these current crescents are shorter and less prominent than the backwash-oriented arms. The shorter arms open landward whereas the longer arms open seaward. They generally form around obstacles like armoured mud balls, polychaete tubes, tussocks etc. which are partially set in a scour implying greater anchoring or a semipermanent nature. These current crescents occur on fine to very find sandy beaches (Mz = 2.9 to 3.1 Φ) with a beach slopes of 1:50 to 1:90 (1.4-0.7°). They are very commonly associated with current lineations. The arms of crescents parallel current lineations and are at right angles to the shoreline. In contrast, ordinary backwash-oriented current crescents form on steeper beach slopes, 1:9 to 1:25 (6−3°), in fine to medium sand(Mz = 1.8 to 2 Φ). They occur around tiny obstacles which are easily swept away by wave swash and backwash.

Mercury Concentration in Sediment Cores from Sundarban Mangrove Wetland, India

The work presents an extended database (n = 123) of total mercury (THg) in fine-grained sediment fraction (<63 μm) of core samples in 10 sampling stations of the Sundarban mangrove wetland, India, formed at the estuarine realm of the Hugli (Ganga) River. Results revealed a wide range of spatial, seasonal, and intertidal flat variations of THg (7.3 to 93.3 ng/g) with a definite enhancement level at the lower stretch of the estuary, which has extreme mangrove vegetation. An overall enrichment of THg in surface/subsurface layers of the core is tentatively explained by remobilization and resuspension of the metal from deeper sediments (36–40 cm). A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while correlations of Hg with organic carbon was poor. Based on the index of geoaccumulation (Igeo), enrichment factor (EF), and anthropogenic factor (AF) values, it is suggested that the sediments of Sundarban were found to be less polluted with respect to total mercury. The data reported are a useful baseline for THg in Sundarban and would be of importance in future sediment quality studies.

Persistent Organic Pollutants (POPs) in Sediments and Biota in Coastal Environments of India

Persistent organic pollutants (POPs) are semivolatile organic compounds of special concern because of their toxicity, persistence, long-range transport and bioaccumulation potential. They are present in the marine environment, notably in coastal areas affected by municipal sewage, agricultural and aquaculture effluents, industry and shipping traffic. The 7,555 km-length coastal region of India is the most vulnerable zone facing frequent geohazards, e.g. tsunami and flooding. It is contaminated from direct discharge of wastes from the densely populated coastal areas, runoff of fertilizers, dumping by vessels, oil spills, deforestation and ill-planned river basin developments. This chapter summarizes the knowlegde on residues of 5 classes of persistent organic pollutants (POPs) such as dichlorodiphenyltrichloroethane and its metabolites (DDTs), hexachlorocyclohexane and its isomers (HCHs), polycyclic aromatic hydrocarbon and its congeners (PAHs), polychorinated biphenyl and its congeners (PCBs) and polybrominated diphenyl ether and its congeners (PBDEs) in the sediments and in selective biota: bivalve mollusks, fishes and marine mammals. Their potential ecotoxicological impacts on biota have also been assessed based on the sediment quality guidelines (SQG) specified by USEPA (The incidence and severity of sediment contamination in surface waters of the United States, vol 1, National sediment quality survey. EPA 823-R-97-006, Washington, DC, 1997a: Environmental protection agency, National Sediment Quality Survey, App D, Washington DC, 1997b) and by Canadian Council of Ministers of the Environment (CCME, Canadian quality guidelines for the protection of aquatic life-summary tables. Available from. http://www.ccme.ca/assets/pdf/sed summary_table.pdf, 2002).

Studies on the role of salt-tolerant plants in the formation and stabilization of coastal dunes of the deltaic Sunderbans, North-East coast of India

Salt-tolerant grasses, herbs and creepers in the supratidal coastal zones in and around the Hooghly-Matla estuarine delta complex of West Bengal, India have been studied with special reference to their manifold roles in the formation of coastal dunes which act a wall of defence for the inland areas against destructive sea waves and currents. (i) The roots and rootlets of the coastal plants act as sand binders; (ii) their leaves and stems help growth of dunes by accumulation of suspensional sand from fall-out; (iii) the type of plants helps stabilization of dunes by arresting dune migration to a considerable extent.