Kuttanad is one of the Ramsar sites in India popular for paddy cultivation below sea level and fish cultivation. Most people rely on these two practices for livelihood. So seasonal fluctuations in physicochemical parameters such as Dissolved Oxygen, Biochemical Oxygen Demand, Temperature, pH, Salinity, Total Dissolved Solids, Electrical Conductivity, Chloride, Phosphate, and Nitrate will influence the fish diversity thereby impact the economic stability of the society. Kuttanad comprises both fresh water and brackish water ecosystem. The western side of the Kuttanad ecosystem ends up with the Arabian Sea. So five major rivers flowing through Kuttanad from east-west direction joins with Vembanad estuary which opens into the Arabian Sea. Proximity to the sea and geographical elevation causes seasonal saline intrusion into the inland water bodies. It will change the physicochemical properties and decreases the fish diversity seasonally.
There are three main seasons, pre-monsoon (March to May), monsoon (June to November), and post-monsoon (December to February) showing different diversity, in which monsoon season shows a high diversity followed by post monsoon and pre monsoon. Saline intrusion happening in post monsoon and pre monsoon seasons, changes the physicochemical parameters which are significantly correlated (p<0.01 and p<0.05) with fish diversity. Diversity indices such as Shannon Weinner, Simpson’s diversity, Hill’s number, Alpha diversity, and Margalef’s index were calculated for the study. The study was conducted over 3 years as a part of Ph.D. research.
Among the 63 identified species 30 species significantly correlated with DO, 19 species with BOD, 9 species with chloride, 19 species with phosphate, 31 species with nitrate, 31 species with pH, 34 species with EC, 33 species with TDS, 14 species with salinity, and 19 species with temperature. Out of the 63 species, 2 species Clarias gariepinus and Oreochromis mossambicus are invasive alien species. Saline intrusion during post monsoon season declines primary productivity or phytoplankton diversity thereby zooplankton diversity and finally ends up with low fish diversity.
Recent studies investigate the impact of arctic ice melting due to global warming causes surface cyclonic circulation in the Arabian Sea which enhances the moisture convergence, eventually leads to extreme extended monsoon rain in Kerala. So the impact of global warming on the fish diversity of Kerala has to be studied immediately.