Seasonal variability in physicochemical parameters and fish larval abundance along the coastal waters of Dakshina Kannada, southwest coast of India

The study attempted to record the seasonal variability in the physicochemical parameters that influence the fish larval abundance in six stations from the Netravathi-Gurupura and the Mulki-Pavanje estuaries along the coast of Dakshina Kannada for a period of 36 months (2014)(2015)(2016).Pronounced variations in the primary production, chlorophyll a, and physicochemical parameters such as water temperature, pH, salinity, dissolved oxygen, and nutrients were observed in the estuarine and coastal waters.Between stations, the one-way ANOVA revealed highly significant variations (p<0.001) in pH, salinity, Chlorophyll a, Nitrate-N, Ammonia-N, and Silicate-Si concentrations and significant differences in dissolved oxygen and chlorophyll c (p< 0.05) concentrations.Multivariate comparisons (Tukey HSD) revealed variations in the physicochemical parameters within the stations.Nearshore stations and estuarine waters were distinct concerning physicochemical parameters.Environmental factors influencing fish larval abundance in the nearshore waters include rainfall (r = 0.487, p< 0.01), river discharge (r = 0.444, p< 0.01), dissolved oxygen (r = 0.395, p< 0.05), and silicate-Si concentration (r = 0.423, p<0.05).Similarly, the tidal height (r= 0.536, p<0.01) also played an additional key role in influencing and determining the seasonal abundance of fish larvae in the estuarine waters.The water quality index (WQI) in estuaries and nearshore waters is indicated as Good to Poor state as per USEPA (2012) rating.Improving the quality of near-shore coastal waters can increase the survival of fish larvae, protect fish breeding sites, and ultimately contribute to enhanced fisheries productivity.