N. C. Nandi

Distribution and Abundance of Macrozoobenthic Species in Some Tropical Brackishwater Wetlands of West Bengal, India

Benthos inhabiting brackishwater ecosystems is subjected to transitional environment of freshwater and saltwater conditions. In the present paper the effects of environmental variables were studied along with anthropogenic activities, selecting two man-made fishery systems (bheri) and one natural estuarine system at Canning town, West Bengal, India. 11 water parameters and five sediment parameters were studied. Qualitative study of macrozoobenthos indicates that natural estuarine ecosystem harbours 57 species of nine groups while brackishwater impoundments are inhabited by 17–20 species only. The population density of the commonly occurring macrobenthic species reveals variation with respect to season and sites. Pearson’s correlation coefficient analysis and canonical correspondence analysis results suggest that more than 15 macrozoobenthic species bear significant correlation with one or more water and sediment parameters, within which 12 species showed significant correlation in estuarine ecosystem indicating more environmental stress in impoundments than estuary.

Macrozoobenthic Community and Assessment of Aquatic Ecosystem Health of three Waterbodies of East Calcutta Wetlands, India

The present study was aimed to understand the diversity, abundance and distribution of macrozoobenthic community of three selected fishponds differing in sewage intake and culture practices of East Calcutta Wetlands of Kolkata, India, as well as the aquatic ecosystem health of these waterbodies considering benthos as the best indicator of pollution. One year seasonal samplings were done to study the diversity and distribution of macrozoobenthos along with 12 water quality parameters to reflect the ecological conditions and aquatic ecosystem health of these waterbodies through biodiversity indices and statistical analysis (SPSS 10). A total of 27 species of macrozoobenthic organisms belonging to 18 families under four phyla comprising eight major groups viz. Polychaeta, Oligochaeta, Hirudinea, Diptera, Odonata, Gastropoda, Bivalvia and Pisces have been recorded. The diversity of macrozoobenthic fauna of these three waterbodies revealed that Ruby wetland had the highest representation of 24 species followed by Sukantanagar pond (17 species) and Sukantanagar bheri (16 species). The result of Pearson’s correlation coefficient showed that amongst the collected macrozoobenthos the gastropod species, Bellamya bengalensis and Lymnaea acuminata were wetland site-wise significant. The total benthic population and biomass have positive correlation with water transparency and organic enrichment of the waterbody. Shannon Weiner and Margalef’s indices have revealed higher values for Ruby wetland. Biodiversity indices and BMWP Score System designated to benthic organisms, suggested Ruby wetland is healthier than the other two waterbodies, differing in sewage intake and culture practices.

Effect of insolation and overhead canopy on macrozoobenthos of tropical freshwater ponds.

Distribution and abundance of macrozoobenthic species were investigated in open and shaded sites of tropical freshwater pond ecosystems in Kolkata. Water temperature of open sites was higher than the shaded sites but transparency value was lower at the lighted sites presumably related with the production of phytoplankton in the presence of sunlight. Diversity of species was recorded highest (26 species) along with total benthos density (5999 no/m2) at slightly illuminated open site. Mean biomass was also highest at the slightly illuminated open site. Total benthos density of macrozoobenthos was lower at the fully shaded and fully lighted sites. The greater occurrence and abundance of most macrozoobenthic species-including total benthos density and biomass at the slightly illuminated open site was probably associated with microhabitat suitability supported by moderate presence of macrophytes. Higher quality food (algae and algal detritus) and thermal suitability as well as phototactic attraction of motile epibenthic gastropods and other organisms contribute to the greater abundance and production of biomass at this site.