Phytoplankton dynamics in estuarine waters of central Kerala, south west India

A three-year investigation into the dynamics of phytoplankton was carried out in central Kerala, India's Munambam and Chettuva estuaries. In order to comprehend the link between phytoplankton species and their affecting physico-chemical factors, a seasonally-based study was conducted from pre-monsoon 2017 to monsoon 2019. A total of 144 phytoplankton species come under the taxonomic classes Bacillariophyceae, Chlorophyceae, Dinophyceae, Cyanophyceae and Chrysophyceae. Diatoms represented the dominant class. Dinoflagellates are represented next to diatoms in estuaries, mainly in pre-monsoon season. Several species were recorded as the highest in pre-monsoon season in estuarine stations and the species diversity was high in 2017. Nitzschia and Navicula were the most prevalent diatom species at estuary stations, as they are widely distributed in both coastal and estuarine environments. The Dinophycean distribution especially showed close association with seasonal saline fluctuation in estuaries and they represented mainly in pre-monsoon season. Seven potentially harmful or bloom-forming species were also found to be present in low concentrations at the sample stations. The catastrophic flood in Monsoon 2018 in Kerala affected the diversity of species to a major extent. The species diversity was recorded high at the Munambam estuary than Chettuva. The flood driven nutrient status influenced the species composition of phytoplankton. The dominance of fast-growing colonial diatoms, after the flood authenticate this finding. Statistical tools such as Cluster Analysis and Canonical Correspondence Analysis was also employed to substantiate the species similarity and influence of hydrological factors with phytoplankton groups.