Response of coastal phytoplankton to upwelling induced hydrological changes in the Alappuzha mud bank region, southwest coast of India

•First-time study regarding the size-structure based productivity patterns in the Alappuzha nearshore waters, located in the southwest coast of India, using a time series field-based data.•Addressed not only the upwelling induced phytoplankton growth patterns, but also the influence of suspended sediments on the overall phytoplankton community growth brought by the mud banks prevalent during the southwest monsoon period.•The study revealed the predominance of the nanophytoplankton community (in terms of chlorophyll a biomass and primary production) all through the study region, irrespective of seasons.