Spatial and temporal dynamics of phytoplankton in association with habitat parameters in a tropical reservoir, India

Phytoplankton, the primary producers in an aquatic ecosystem, also act as indicators of pollution by alterations in species composition and population structure. Study on plankton dynamics in relation to environment forms the base of any aquatic ecosystem management. So, a study on the variations in the plankton population influenced by abiotic factors was conducted in the Paleru Reservoir, India. A total of 48 plankton genera belonging to 9 classes were recorded. The Shannon-Wiener diversity index ranged from 1.098 to 2.615 with temporal variations. Plankton density showed significant (p ≤ 0.05) spatial variations with the highest density at the cage site irrespective of the season (4.126 × 105 ± 199 cells/litre, 2.814 × 105 ± 72.5 cells/litre and 3.197 × 105 ± 52.5 cells/litre during pre-monsoon, monsoon and post-monsoon, respectively). Seasonal analysis revealed significantly (p ≤ 0.05) high plankton density during pre-monsoon, followed by post-monsoon and monsoon respectively. The reservoir is moderately polluted as established from the diversity index and the Algal Genus Pollution Index except at the cage site where it receives a polluted status. The relationship of plankton distribution with the environment was established employing canonical correspondence analysis and correlation coefficient. Phosphate-P, nitrate-N, transparency, hardness, pH and dissolved oxygen are the major abiotic factors influencing the plankton distribution in Paleru. Even though Cyanophyceae dominated the plankton population, there was no plankton bloom-associated toxicity, indicating the health and dynamic nature of the reservoir. However, significantly high plankton density indicating a polluted status at the cage site reveals the influence of cage culture.