Environmental factors driving phytoplankton assemblage pattern and diversity: insights from Sundarban eco-region, India

Abstract

Present study dealt with the relative influence of environmental factors on phytoplankton assemblage pattern and diversity in Indian Sundarbans. Analysis revealed, five parameters (temperature, DO, salinity, PO 4 −P and transparency) varied significantly between seasons ( p ≤0.05). Out of 84 species (62 genera), diatoms dominated across the seasons with maximum contribution from pennales (22 genera). Coscinodiscophyceae exhibited prominence in terms of abundance (2.501 × 10 3 ±1.04 × 10 3 org.L −1 ) and Bacillariophyceae in diversity (29 species). ANOVA (post-hoc test) showed the significant spatio-temporal heterogeneity ( p ≤0.05) of phytoplankton distribution in the system. Seasonal abundance revealed maximum in monsoon (3.347 × 10 3 ±1.948 × 10 3 org.L −1 ). Cluster analysis showed three clusters among the stations with maximum similarity between Jharkhali and Nischintapur. NMDS portrayed overall 40% similarity among all the stations. Furthermore, the resemblance of community compositions was observed between Pathar Pratima and Frazerganj, which might be due to geographical proximity between the stations and similar magnitude of salinity throughout the study period. Water parameters viz., temperature, total alkalinity, salinity, PO 4 −P, SiO 4 −Si and SO 4 2− were the deterministic parameters influencing the distribution of phytoplankton, which was evident from BIO-ENV and Marginal test. Furthermore, the distance based linear model (DistLM) model explained two variables viz., PO 4 −P and total alkalinity were the controlling variables that could explain the phytoplankton community compositions in Sundarbans. Shannon diversity index indicated moderately rich phytoplankton diversity in the system with a calculated value >2.78. Index of multivariate dispersion (IMD) value also depicted increase in the community variability with the dispersion value of – 0.431.