Occurrence of potentially toxic cyanobacteriaMicrocystis aeruginosain aquatic ecosystems of central Kerala (south India)

Microcystis aeruginosais a potentially toxic bloom-forming freshwater cyanobacterium, usually found in eutrophic water bodies worldwide. The present study reports the occurrence ofMicrocystis aeruginosaand 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 theM. aeruginosablooms were recorded from two freshwater ponds of Kochi. Massive blooms ofM. aeruginosawas observed during the period prior to summer monsoon (May) with an abundance of 1.17 × 106cells L‑1(Station 1) and during early summer (February) latter being more thick scum (2 × 108cells L‑1) with high chlorophylla. Dense aggregates ofM. aeruginosascums were more prevalent during the periods characterised by higher Surface Water Temperature (SWT). The nutrient characteristic pattern of the study area showed the abundance ofM. aeruginosacorrelated 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 cyanobacteriaM.aeruginosa.Toxicological studies conducted revealed that theMicrocystisbloom was hepatotoxic, inflicting fish mortality.