Studies on the diversity and ecology of zooplankton population in Sundarban Estuarine System (SES), West Bengal, India

Abstract

Zooplankton play pivotal role in estuarine ecosystem. The relative importance of different environmental parameters in determining the diversity and ecology of zooplankton have been investigated from Sundarban Estuarine System (SES), India. The initial observation was designed to decipher the effect of monsoon on zooplankton species diversity, abundance along with physiochemical factors at river Saptamukhi of SES. Significant intra-monsoonal changes of zooplankton population correlated with several environmental parameters were documented. Additionally, the spatial-temporal distribution of zooplankton were recorded based on different multivariate statistics and indicator value (IndVal) analysis from the river Matla in the eastern part of SES. Seasonal occurrence of dominant taxa with high IndVal index was noticeably observed and it can be used as potential bioindicator for particular season and environmental condition in this estuarine system. Exclusive occurrence of warm water species indicated that the area is under threat of climate change mediated temperature rise. Altogether, 56 zooplankton taxa were identified with copepods forming the predominant population. The zooplankton density was highest in winter, followed by monsoon, summer and spring. Different time series observations were also carried out to unravel the specific diel and tidal variations of economically important shellfish larvae. It has been established that, their early developmental stages utilize the tidal currents for ingress and egress mechanisms in order to migrate horizontal distances and/or remain in their preferred habitats. Moreover, Metapenaeus dobsoni was also selected as a proxy to understand the diel, tidal and ontogenetic changes in their abundance within SES during two different tidal phases. Finally, the impact of climate change mediated elevated temperature on the physiology of a meroplankton species has been assessed through mesocosm experiment by using Penaeus monodon post larvae as a model organism. The growth, survival percentages, ingestion and absorption rate were decreased; howbeit respiration and ammonia excretion rate had been increased in elevated temperature resulted a negative Scope for Growth in stressful environment. The present work provides a benchmark for Sundarban zooplankton species diversity and distribution as well as their diel and tidal variations with respect to different environmental parameters for planning suitable conservation strategies and sustainable development in future.