The overall goal of this project is to identify the key cellular processes involved in harmful algal blooms (HABs), commonly known as red tides. HABs pose a major threat to human health, ecosystem health, and fisheries resources throughout the world. One of the most important model systems for studying this process is the toxic dinoflagellate Alexandrium tamarense, a unicellular alga that produces neurotoxins that cause paralytic shellfish poisoning, and is the most widespread of all HAB poisoning syndromes. With the recent development of genomic resources for A. tamarense, it is now possible to conduct studies on the environmental regulation of gene expression in this important species, and to begin to unravel the mysteries of bloom dynamics and cellular metabolism at a level that has never before been possible. This project will identify transcriptionally regulated genes and pathways during the three general stages of a bloom: initiation, development, and termination. Specifically, the investigators will create a microarray for A. tamarense to: 1. identify the key genes involved in the initiation of A. tamarense blooms, specifically those regulated during the germination of resting cyst life stages; 2. identify the key genes involved in the development and maintenance of A. tamarense blooms, specifically those involved in the assimilation of organic and inorganic nutrients, the process of photosynthesis, the production of toxins, and cell division cycle; 3. identify the key genes involved in the termination of A. tamarense blooms, specifically those regulated in response to nutrient limitation, and during the transition from vegetative growth to the sexual cycle that results in resting stage formation;and 4. investigate the physiological state of dinoflagellate cells in situ, by comparing expression profiles of a natural bloom population with the data generated from laboratory cultures. This study is an integrated, collaborative program that relies on expertise in A. tamarense molecular evolution, genomics, physiology, ecology, and toxicity. The investigators hope to produce a valuable molecular resource for scientists working to understand the ecology and toxicity of A. tamarense and other HAB species as well as help train the next generation of scientists working on this important problem. Additionally, the results of these studies will provide insights into the unique genome of these fascinating, evolutionarily and economically important, yet understudied organisms.