Lingulodinium polyedrum is a marine, bioluminescent dinoflagellate that is a common red tide species and potential toxin producer (yessotoxin) along a large expanse of the coast of Southern California. Little is known about the factors leading to bloom formation, or its impact on planktonic food webs. Bloom abundances can reach over 1000 cells/ml, events in which the interplay of physical forces (wind and surface currents) and of algal behavior (vertical migration) presumably play an important role. Using the CENS laboratory test bed, we have examined the pattern and timing of vertical migration by the dinoflagellate in a 2m water column on an 11h:13h light:dark photoperiod. Species-specific detection and enumeration of this organism was accomplished using an 18S rDNA-based quantitative real-time PCR (qPCR) approach developed in our lab. Positive phototaxis of L. polyedrum resulted in dense aggregations of the dinoflagellate within the top few centimetres of the water column during the light period, while cells were evenly distributed during the night.