Occurrence of potentially toxic cyanobacteria Microcystis aeruginosa in aquatic ecosystems of central Kerala (south India)

Microcystis aeruginosa is a potentially toxic bloom-forming freshwater cyanobacterium, usually found in eutrophic water bodies worldwide. The present study reports the occurrence of Microcystis aeruginosa and its bloom in freshwater ponds along central Kerala (south India). Monitoring of cyanobacterial blooms was conducted from May 2019 to February 2020 along the aquatic ecosystems of central Kerala and the M. aeruginosa blooms were recorded from two freshwater ponds of Kochi. Massive blooms of M. aeruginosa was observed during the period prior to summer monsoon (May) with an abundance of 1.17 × 106 cells L‑1 (Station 1) and during early summer (February) latter being more thick scum (2 × 108 cells L‑1) with high chlorophyll a. Dense aggregates of M. aeruginosa scums were more prevalent during the periods characterised by higher Surface Water Temperature (SWT). The nutrient characteristic pattern of the study area showed the abundance of M. aeruginosa correlated very well with higher dissolved nitrate (96.7 μmol L‑1) and phosphate (19.88 μmol L‑1) concentrations. Thus in the stable freshwater ponds with higher SWT and nutrients were the major factors influencing the growth and abundance of the cyanobacteria M. aeruginosa. Toxicological studies conducted revealed that the Microcystis bloom was hepatotoxic, inflicting fish mortality.