As part of their sexual life cycle form dinoflagellate species form resistant resting stages (hypnozygote cysts) which are important in their ecology. The factors inducing sexual reproduction (and hence encystment) have not been clearly defined and conflicting information exists from laboratory and field observations. Nutrient deficiency in growth medium is commonly used in laboratory dinoflagellate cultures to induce sexual reproduction, but field observations of encystment have been made in conditions of apparent nutrient sufficiency. The aim of this project is to investigate the factors which trigger sexual reproduction in coastal dinoflagellates.