Tracking the history of dinoflagellate cyst assemblages in sediments from the west coast of India

► First temporal record (dated till1856 AD) of dinoflagellate cyst from Indian coast. ► Higher Gonyaulax cysts from 130 to 38 cm indicate autotrophic bloom event in past. ► Cyst reduction coeval with shift in organic matter type, possibly monsoon driven. ► Shift from auto- to heterotrophic cyst forms suggests ecosystem changes with time. ► Cysts of potential harmful forms were present in sediments older than 20th century.