Quantification and Visualization of the Variability of Phytoplankton Assemblage in a Semi-lotic Seasonal Canal in Sundarbans, India

Abstract

Canals of Sundarbans in India are highly vulnerable to anthropogenic pressures which directly or indirectly impact the biological components of such ecosystems. Being at the base of the trophic pyramid, phytoplankton is exposed to environmental stressors and the impact will be reflected in the upper strata of the aquatic food chain. Hence, phytoplankton communities along with their interrelationship with environmental parameters were assessed in Bhetkimari canal, a semi-lotic system in Indian Sundarbans during June 2017 to September 2018. Seventy-seven species under 66 genera were recorded with Cyanophyceae (34%) as a major contributor, followed by Bacillariophyceae (31%) and Chlorophyceae (22%). Diatoms dominated round the year in terms of diversity (25 species) with maximum contribution from Pennales. ANOVA (post-hoc test) showed significant temporal heterogeneity (p≤0.05) in phytoplankton distribution in the canal. The Margalef richness index (d) and Shannon-Weiner diversity index ( H′ ) were 2.59±0.43 and 2.26±0.59, respectively indicating that the environment is good and phytoplankton diversity in the system is moderate. Water temperature, dissolved oxygen, total alkalinity and nutrients (nitrate, silicate and phosphate) were the explanatory variables in shaping the phytoplankton assemblages in the canal, which was evident from Canonical correspondence analysis. The salient findings of this study can add to the existing knowledge on the abundance and distribution pattern of phytoplankton in semi-lotic canal environments, and help in planning better management of canal ecosystems for their sustainable utilization.