The seasonal variation and the effect of physico-chemical factors on  cyanobacterial diversity along Cochin backwater were studied during 2002-2004. In all, 75 species of cyanobacteria from 24 genera across 7 families and 4 orders of the class Cyanophyceae were recorded. Of these thirty one species were unicellular colonial forms, 43 were filamentous forms without heterocyst and two were heterocystous filamentous forms. The predominant species observed were Chroococcus turgidus, Chroococcus tenax, Synechococcus elongatus, Synechocystis salina, Oscillatoria foreaui, Oscillatoria remyii, Oscillatoria pseudogeminata, Oscillatoria subtillissima, Oscillatoria willei, Phormidium purpurescens and Phormidium tenue. Water temperature, salinity and euphotic depth had a positive correlation with the cyanobacterial density, whereas, nutrients had a negative impact when they were in excess. Pre-monsoon season was characterised by high density of these organisms, whereas, cell count was very low during monsoon season. All the backwater stations and the mangrove station showed significantly higher cyanobacterial community when compared to sea shore site which suggests that the ecological conditions of Cochin estuary support a rich cyanobacterial flora.

Species diversity, cyanobacteria, Cochin estuary