Studies on Ecology of Soft-Bottom Meiobenthic Community from Sundarban Estuarine System, West Bengal, India

Abstract

Structure of meiobenthic assemblage was assessed for the first time from world’s largest mangrove ecosystem, Sundarbans, focusing on free living nematode species composition (~ 90% of the total population). The present research revealed the deleterious effect of excessive monsoonal rain on meiobenthos as well as free-living nematode assemblages. Abundance of meiobenthos declined from early monsoon to later period of monsoon due to massive riverine runoff followed by cloudburst phenomenon that completely flushed the estuary. Significant temporal and spatial heterogeneity in the abundance of meiobenthos and nematode species composition was also described in relation with environmental variables. Distinct seasonal fluctuation of meiobenthos was prominent due to seasonal changes in sedimentary environment. Nematodes dominated the meiobenthic assemblages, ranking harpacticoid copepod in the second position. Altogether, 79 species of free-living nematode had been identified for the first time and nematode assemblage was dominated by Sabatieria preadatrix, Sphaerolaimus bulticus, Desmodora communis, Dorylaimopsis punctata and Daptonema hirsutum. Biological trait approach of nematode assemblages was applied to investigate the ecological functioning based on morphological and ecological characteristics, which added relevant information regarding relationships between species diversity and the abiotic environment. Furthermore, present study conducted a pioneering survey regarding vertical stratification of meiobenthic assemblages in different mangrove vegetation with nematofaunal species level information. This study clearly depicted that more than 90% of faunal populations was concentrated within upper 3-4 cm of sediment, though they were present up to 15 cm of depth. Furthermore, combined effect of climate change mediated elevated temperature and petroleum pollution on meiobenthic organisms were also investigated through a benthocosm experiment. The present research highlighted harmful effects of these stressors on meiobenthic species composition and abundance. Present observation would be a maiden footstep to understand the resilience of meiobenthic organisms to predicted climate change scenarios. Altogether the present thesis provided blended information about the succession pattern of meiobenthic community structure along with environmental parameters and illustrated the detrimental effect of climate change and anthropogenic perturbation on meiobenthos from Sundarbans. This overview represents a first step to implement a baseline data that could help identifying information gaps and directing future research priorities simultaneously.