Heavy metals pollution influence the community structure of cyanobacteria in nutrient rich tropical estuary
Anthropogenic inputs influence the community structure and activities of microorganisms, which may impinge the functioning of estuarine and coastal ecosystem. The aim of the present study was to understand the influence of dissolved heavy metals (Cr, Mn, Fe, Ni, Cu and Zn) on community structure of cyanobacteria in a nutrient rich tropical estuary, Cochin Estuary (CE), across the southwest coast of India. Dissolved heavy metals were higher in CE during dry season, with Zn as major pollutant. The level of dissolved Zn was higher in stations near river head during dry (130 µg L-1) and wet seasons (105 µg L-1). The community structure of cyanobacteria was higher in CE during wet season (H’ index: 1.4 to 3.1) compared to that in dry season (H’ index: 1.1 to 2.2). The 16S rRNA gene sequence analysis showed the prevalence of Synechococcus sp in CE. PCA analysis indicated the positive influence of Zn and nutrients on community structure of cyanobacteria. We postulate that the Zn pollution may be a critical factor to be monitored and controlled in nutrient rich estuaries, otherwise it may accelerate the eutrophication and associated ecological constraints.