We use marine and freshwater algal cells as model systems for studying basic cell and molecular biological questions. Most recently, we have been investigating the molecular genetic basis for harmful blooms of the golden alga (Prymnesium parvum) that have been causing massive fish kills in Texas and around the globe. Using DNA microarray technology, research is aimed at discovering which genes and metabolic pathways are associated with bloom formation and decline, and with levels of toxicity. In this way, molecular biomarkers will be identified for characterizing the metabolic status of this alga using field-collected samples. Also, real-time PCR assays have been developed for DNA-based detection and quantification of this organism, providing the basis for a statewide survey of all major watersheds.