Quantitative observations of Cyanobacteria and Dinoflagellata in reservoirs of Sri Lanka

Cyanobacterial and dinoflagellate blooms have a range of social, environmental and economic impacts due to their potential of toxin production under extreme environmental conditions. Therefore, the present study aimed to understand the species abundance, distribution and the relationship between species distribution and measured environmental variables within the 45 reservoirs studied, covering three major climatic regions of Sri Lanka (Wet, Intermediate and Dry). Plankton samples were obtained using a 34μm plankton net. Both field and laboratory analyses were conducted to obtain limnological data of each reservoir. Multivariate statistical techniques were used to understand the species distribution along measured environmental gradients. Thirteen species of Cyanobacteria were identified and seven of them were toxigenic. The Dry Zone showed the highest diversity of Cyanobacteria including toxigenic species and the Wet Zone showed the lowest. While Cylindrospermopsis raciborskii was the dominant species recorded in 22% of the sampled reservoirs, Pseudoanabaena limnetica was the least dominant. Only one species of Dinoflagellate, Peridinium aciculiferum was identified from all the climatic regions. Multivariate statistical analysis revealed that temperature is the most important environmental variable that determines the species variation and abundance among the sites.